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rfc:rfc3626

Network Working Group T. Clausen, Ed. Request for Comments: 3626 P. Jacquet, Ed. Category: Experimental Project Hipercom, INRIA

                                                          October 2003
            Optimized Link State Routing Protocol (OLSR)

Status of this Memo

 This memo defines an Experimental Protocol for the Internet
 community.  It does not specify an Internet standard of any kind.
 Discussion and suggestions for improvement are requested.
 Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

 This document describes the Optimized Link State Routing (OLSR)
 protocol for mobile ad hoc networks.  The protocol is an optimization
 of the classical link state algorithm tailored to the requirements of
 a mobile wireless LAN.  The key concept used in the protocol is that
 of multipoint relays (MPRs).  MPRs are selected nodes which forward
 broadcast messages during the flooding process.  This technique
 substantially reduces the message overhead as compared to a classical
 flooding mechanism, where every node retransmits each message when it
 receives the first copy of the message.  In OLSR, link state
 information is generated only by nodes elected as MPRs.  Thus, a
 second optimization is achieved by minimizing the number of control
 messages flooded in the network.  As a third optimization, an MPR
 node may chose to report only links between itself and its MPR
 selectors.  Hence, as contrary to the classic link state algorithm,
 partial link state information is distributed in the network.  This
 information is then used for route calculation.  OLSR provides
 optimal routes (in terms of number of hops).  The protocol is
 particularly suitable for large and dense networks as the technique
 of MPRs works well in this context.

Clausen & Jacquet Experimental [Page 1] RFC 3626 Optimized Link State Routing October 2003

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1. OLSR Terminology.  . . . . . . . . . . . . . . . . . . .   5
     1.2. Applicability. . . . . . . . . . . . . . . . . . . . . .   7
     1.3. Protocol Overview  . . . . . . . . . . . . . . . . . . .   8
     1.4. Multipoint Relays  . . . . . . . . . . . . . . . . . . .   9
 2.  Protocol Functioning  . . . . . . . . . . . . . . . . . . . .   9
     2.1. Core Functioning   . . . . . . . . . . . . . . . . . . .  10
     2.2. Auxiliary Functioning  . . . . . . . . . . . . . . . . .  12
 3.  Packet Format and Forwarding  . . . . . . . . . . . . . . . .  13
     3.1. Protocol and Port Number.  . . . . . . . . . . . . . . .  13
     3.2. Main Address   . . . . . . . . . . . . . . . . . . . . .  13
     3.3. Packet Format  . . . . . . . . . . . . . . . . . . . . .  14
          3.3.1. Packet Header . . . . . . . . . . . . . . . . . .  14
          3.3.2. Message Header  . . . . . . . . . . . . . . . . .  15
     3.4. Packet Processing and Message Flooding . . . . . . . . .  16
          3.4.1. Default Forwarding Algorithm. . . . . . . . . . .  18
          3.4.2. Considerations on Processing and Forwarding . . .  20
     3.5. Message Emission and Jitter. . . . . . . . . . . . . . .  21
 4.  Information Repositories  . . . . . . . . . . . . . . . . . .  22
     4.1. Multiple Interface Association Information Base  . . . .  22
     4.2. Link sensing: Local Link Information Base. . . . . . . .  22
          4.2.1. Link Set. . . . . . . . . . . . . . . . . . . . .  22
     4.3. Neighbor Detection: Neighborhood Information Base. . . .  23
          4.3.1. Neighbor Set. . . . . . . . . . . . . . . . . . .  23
          4.3.2. 2-hop Neighbor Set. . . . . . . . . . . . . . . .  23
          4.3.3. MPR Set . . . . . . . . . . . . . . . . . . . . .  23
          4.3.4. MPR Selector Set. . . . . . . . . . . . . . . . .  23
     4.4. Topology Information Base  . . . . . . . . . . . . . . .  24
 5.  Main Addresses and Multiple Interfaces  . . . . . . . . . . .  24
     5.1. MID Message Format . . . . . . . . . . . . . . . . . . .  25
     5.2. MID Message Generation . . . . . . . . . . . . . . . . .  25
     5.3. MID Message Forwarding . . . . . . . . . . . . . . . . .  26
     5.4. MID Message Processing . . . . . . . . . . . . . . . . .  26
     5.5. Resolving a Main Address from an Interface Address . . .  27
 6.  HELLO Message Format and Generation . . . . . . . . . . . . .  27
     6.1. HELLO Message Format . . . . . . . . . . . . . . . . . .  27
          6.1.1. Link Code as Link Type and Neighbor Type. . . . .  29
     6.2. HELLO Message Generation . . . . . . . . . . . . . . . .  30
     6.3. HELLO Message Forwarding . . . . . . . . . . . . . . . .  33
     6.4. HELLO Message Processing . . . . . . . . . . . . . . . .  33
 7.  Link Sensing  . . . . . . . . . . . . . . . . . . . . . . . .  33
     7.1. Populating the Link Set  . . . . . . . . . . . . . . . .  33
          7.1.1. HELLO Message Processing  . . . . . . . . . . . .  34
 8.  Neighbor Detection  . . . . . . . . . . . . . . . . . . . . .  35
    8.1. Populating the Neighbor Set . . . . . . . . . . . . . . .  35
          8.1.1. HELLO Message Processing  . . . . . . . . . . . .  37

Clausen & Jacquet Experimental [Page 2] RFC 3626 Optimized Link State Routing October 2003

     8.2. Populating the 2-hop Neighbor Set. . . . . . . . . . . .  37
          8.2.1. HELLO Message Processing. . . . . . . . . . . . .  37
     8.3. Populating the MPR set . . . . . . . . . . . . . . . . .  38
          8.3.1. MPR Computation . . . . . . . . . . . . . . . . .  39
     8.4. Populating the MPR Selector Set. . . . . . . . . . . . .  41
          8.4.1. HELLO Message Processing. . . . . . . . . . . . .  41
     8.5. Neighborhood and 2-hop Neighborhood Changes. . . . . . .  42
 9.  Topology Discovery  . . . . . . . . . . . . . . . . . . . . .  43
     9.1. TC Message Format. . . . . . . . . . . . . . . . . . . .  43
     9.2. Advertised Neighbor Set. . . . . . . . . . . . . . . . .  44
     9.3. TC Message Generation. . . . . . . . . . . . . . . . . .  45
     9.4. TC Message Forwarding. . . . . . . . . . . . . . . . . .  45
     9.5. TC Message Processing. . . . . . . . . . . . . . . . . .  45
 10. Routing Table Calculation . . . . . . . . . . . . . . . . . .  47
 11. Node Configuration. . . . . . . . . . . . . . . . . . . . . .  50
     11.1. Address Assignment. . . . . . . . . . . . . . . . . . .  50
     11.2. Routing Configuration . . . . . . . . . . . . . . . . .  51
     11.3. Data Packet Forwarding. . . . . . . . . . . . . . . . .  51
 12. Non OLSR Interfaces . . . . . . . . . . . . . . . . . . . . .  51
     12.1. HNA Message Format. . . . . . . . . . . . . . . . . . .  52
     12.2. Host and Network Association Information Base . . . . .  52
     12.3. HNA Message Generation. . . . . . . . . . . . . . . . .  53
     12.4. HNA Message Forwarding. . . . . . . . . . . . . . . . .  53
     12.5. HNA Message Processing. . . . . . . . . . . . . . . . .  53
     12.6. Routing Table Calculation . . . . . . . . . . . . . . .  54
     12.7. Interoperability Considerations . . . . . . . . . . . .  55
 13. Link Layer Notification . . . . . . . . . . . . . . . . . . .  55
     13.1. Interoperability Considerations . . . . . . . . . . . .  56
 14. Link Hysteresis . . . . . . . . . . . . . . . . . . . . . . .  56
     14.1. Local Link Set  . . . . . . . . . . . . . . . . . . . .  56
     14.2. Hello Message Generation  . . . . . . . . . . . . . . .  57
     14.3. Hysteresis Strategy . . . . . . . . . . . . . . . . . .  57
     14.4. Interoperability Considerations . . . . . . . . . . . .  59
 15. Redundant Topology Information. . . . . . . . . . . . . . . .  59
     15.1. TC_REDUNDANCY Parameter . . . . . . . . . . . . . . . .  60
     15.2. Interoperability Considerations . . . . . . . . . . . .  60
 16. MPR Redundancy. . . . . . . . . . . . . . . . . . . . . . . .  60
     16.1. MPR_COVERAGE Parameter. . . . . . . . . . . . . . . . .  61
     16.2. MPR Computation . . . . . . . . . . . . . . . . . . . .  61
     16.3. Interoperability Considerations . . . . . . . . . . . .  62
 17. IPv6 Considerations . . . . . . . . . . . . . . . . . . . . .  63
 18. Proposed Values for Constants . . . . . . . . . . . . . . . .  63
     18.1. Setting emission interval and holding times . . . . . .  63
     18.2. Emission Interval . . . . . . . . . . . . . . . . . . .  64
     18.3. Holding time  . . . . . . . . . . . . . . . . . . . . .  64
     18.4. Message Types . . . . . . . . . . . . . . . . . . . . .  65
     18.5. Link Types. . . . . . . . . . . . . . . . . . . . . . .  65
     18.6. Neighbor Types  . . . . . . . . . . . . . . . . . . . .  65

Clausen & Jacquet Experimental [Page 3] RFC 3626 Optimized Link State Routing October 2003

     18.7. Link Hysteresis . . . . . . . . . . . . . . . . . . . .  66
     18.8. Willingness . . . . . . . . . . . . . . . . . . . . . .  66
     18.9. Misc. Constants . . . . . . . . . . . . . . . . . . . .  67
 19. Sequence Numbers. . . . . . . . . . . . . . . . . . . . . . .  67
 20. Security Considerations . . . . . . . . . . . . . . . . . . .  67
     20.1. Confidentiality . . . . . . . . . . . . . . . . . . . .  67
     20.2. Integrity . . . . . . . . . . . . . . . . . . . . . . .  68
     20.3. Interaction with External Routing Domains . . . . . . .  69
     20.4. Node Identity . . . . . . . . . . . . . . . . . . . . .  70
 21. Flow and congestion control . . . . . . . . . . . . . . . . .  70
 22. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  70
 23. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  71
 24. Contributors. . . . . . . . . . . . . . . . . . . . . . . . .  71
 25. References. . . . . . . . . . . . . . . . . . . . . . . . . .  73
 26. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . .  74
 27. Full Copyright Statement. . . . . . . . . . . . . . . . . . .  75

1. Introduction

 The Optimized Link State Routing Protocol (OLSR) is developed for
 mobile ad hoc networks.  It operates as a table driven, proactive
 protocol, i.e., exchanges topology information with other nodes of
 the network regularly.  Each node selects a set of its neighbor nodes
 as "multipoint relays" (MPR).  In OLSR, only nodes, selected as such
 MPRs, are responsible for forwarding control traffic, intended for
 diffusion into the entire network.  MPRs provide an efficient
 mechanism for flooding control traffic by reducing the number of
 transmissions required.
 Nodes, selected as MPRs, also have a special responsibility when
 declaring link state information in the network.  Indeed, the only
 requirement for OLSR to provide shortest path routes to all
 destinations is that MPR nodes declare link-state information for
 their MPR selectors.  Additional available link-state information may
 be utilized, e.g., for redundancy.
 Nodes which have been selected as multipoint relays by some neighbor
 node(s) announce this information periodically in their control
 messages.  Thereby a node announces to the network, that it has
 reachability to the nodes which have selected it as an MPR.  In route
 calculation, the MPRs are used to form the route from a given node to
 any destination in the network.  Furthermore, the protocol uses the
 MPRs to facilitate efficient flooding of control messages in the
 network.
 A node selects MPRs from among its one hop neighbors with
 "symmetric", i.e., bi-directional, linkages.  Therefore, selecting
 the route through MPRs automatically avoids the problems associated

Clausen & Jacquet Experimental [Page 4] RFC 3626 Optimized Link State Routing October 2003

 with data packet transfer over uni-directional links (such as the
 problem of not getting link-layer acknowledgments for data packets at
 each hop, for link-layers employing this technique for unicast
 traffic).
 OLSR is developed to work independently from other protocols.
 Likewise, OLSR makes no assumptions about the underlying link-layer.
 OLSR inherits the concept of forwarding and relaying from HIPERLAN (a
 MAC layer protocol) which is standardized by ETSI [3].  The protocol
 is developed in the IPANEMA project (part of the Euclid program) and
 in the PRIMA project (part of the RNRT program).

1.1. OLSR Terminology

 The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC2119 [5].
 Additionally, this document uses the following terminology:
    node
       A MANET router which implements the Optimized Link State
       Routing protocol as specified in this document.
    OLSR interface
       A network device participating in a MANET running OLSR.  A node
       may have several OLSR interfaces, each interface assigned an
       unique IP address.
    non OLSR interface
       A network device, not participating in a MANET running OLSR.  A
       node may have several non OLSR interfaces (wireless and/or
       wired).  Routing information from these interfaces MAY be
       injected into the OLSR routing domain.
    single OLSR interface node
       A node which has a single OLSR interface, participating in an
       OLSR routing domain.
    multiple OLSR interface node
       A node which has multiple OLSR interfaces, participating in an
       OLSR routing domain.

Clausen & Jacquet Experimental [Page 5] RFC 3626 Optimized Link State Routing October 2003

    main address
       The main address of a node, which will be used in OLSR control
       traffic as the "originator address" of all messages emitted by
       this node.  It is the address of one of the OLSR interfaces of
       the node.
       A single OLSR interface node MUST use the address of its only
       OLSR interface as the main address.
       A multiple OLSR interface node MUST choose one of its OLSR
       interface addresses as its "main address" (equivalent of
       "router ID" or "node identifier").  It is of no importance
       which address is chosen, however a node SHOULD always use the
       same address as its main address.
    neighbor node
       A node X is a neighbor node of node Y if node Y can hear node X
       (i.e., a link exists between an OLSR interface on node X and an
       OLSR interface on Y).
    2-hop neighbor
       A node heard by a neighbor.
    strict 2-hop neighbor
       a 2-hop neighbor which is not the node itself or a neighbor of
       the node, and in addition is a neighbor of a neighbor, with
       willingness different from WILL_NEVER, of the node.
    multipoint relay (MPR)
       A node which is selected by its 1-hop neighbor, node X, to
       "re-transmit" all the broadcast messages that it receives from
       X, provided that the message is not a duplicate, and that the
       time to live field of the message is greater than one.
    multipoint relay selector (MPR selector, MS)
       A node which has selected its 1-hop neighbor, node X, as its
       multipoint relay, will be called a multipoint relay selector of
       node X.

Clausen & Jacquet Experimental [Page 6] RFC 3626 Optimized Link State Routing October 2003

    link
       A link is a pair of OLSR interfaces (from two different nodes)
       susceptible to hear one another (i.e., one may be able to
       receive traffic from the other).  A node is said to have a link
       to another node when one of its interface has a link to one of
       the interfaces of the other node.
    symmetric link
       A verified bi-directional link between two OLSR interfaces.
    asymmetric link
       A link between two OLSR interfaces, verified in only one
       direction.
    symmetric 1-hop neighborhood
       The symmetric 1-hop neighborhood of any node X is the set of
       nodes which have at least one symmetric link to X.
    symmetric 2-hop neighborhood
       The symmetric 2-hop neighborhood of X is the set of nodes,
       excluding X itself, which have a symmetric link to the
       symmetric 1-hop neighborhood of X.
    symmetric strict 2-hop neighborhood
       The symmetric strict 2-hop neighborhood of X is the set of
       nodes, excluding X itself and its neighbors, which have a
       symmetric link to some symmetric 1-hop neighbor, with
       willingness different of WILL_NEVER, of X.

1.2. Applicability

 OLSR is a proactive routing protocol for mobile ad-hoc networks
 (MANETs) [1], [2].  It is well suited to large and dense mobile
 networks, as the optimization achieved using the MPRs works well in
 this context.  The larger and more dense a network, the more
 optimization can be achieved as compared to the classic link state
 algorithm.  OLSR uses hop-by-hop routing, i.e., each node uses its
 local information to route packets.
 OLSR is well suited for networks, where the traffic is random and
 sporadic between a larger set of nodes rather than being almost
 exclusively between a small specific set of nodes.  As a proactive

Clausen & Jacquet Experimental [Page 7] RFC 3626 Optimized Link State Routing October 2003

 protocol, OLSR is also suitable for scenarios where the communicating
 pairs change over time: no additional control traffic is generated in
 this situation since routes are maintained for all known destinations
 at all times.

1.3. Protocol Overview

 OLSR is a proactive routing protocol for mobile ad hoc networks.  The
 protocol inherits the stability of a link state algorithm and has the
 advantage of having routes immediately available when needed due to
 its proactive nature.  OLSR is an optimization over the classical
 link state protocol, tailored for mobile ad hoc networks.
 OLSR minimizes the overhead from flooding of control traffic by using
 only selected nodes, called MPRs, to retransmit control messages.
 This technique significantly reduces the number of retransmissions
 required to flood a message to all nodes in the network.  Secondly,
 OLSR requires only partial link state to be flooded in order to
 provide shortest path routes.  The minimal set of link state
 information required is, that all nodes, selected as MPRs, MUST
 declare the links to their MPR selectors.  Additional topological
 information, if present, MAY be utilized e.g., for redundancy
 purposes.
 OLSR MAY optimize the reactivity to topological changes by reducing
 the maximum time interval for periodic control message transmission.
 Furthermore, as OLSR continuously maintains routes to all
 destinations in the network, the protocol is beneficial for traffic
 patterns where a large subset of nodes are communicating with another
 large subset of nodes, and where the [source, destination] pairs are
 changing over time.  The protocol is particularly suited for large
 and dense networks, as the optimization done using MPRs works well in
 this context.  The larger and more dense a network, the more
 optimization can be achieved as compared to the classic link state
 algorithm.
 OLSR is designed to work in a completely distributed manner and does
 not depend on any central entity.  The protocol does NOT REQUIRE
 reliable transmission of control messages: each node sends control
 messages periodically, and can therefore sustain a reasonable loss of
 some such messages.  Such losses occur frequently in radio networks
 due to collisions or other transmission problems.
 Also, OLSR does not require sequenced delivery of messages.  Each
 control message contains a sequence number which is incremented for
 each message.  Thus the recipient of a control message can, if
 required, easily identify which information is more recent - even if
 messages have been re-ordered while in transmission.

Clausen & Jacquet Experimental [Page 8] RFC 3626 Optimized Link State Routing October 2003

 Furthermore, OLSR provides support for protocol extensions such as
 sleep mode operation, multicast-routing etc.  Such extensions may be
 introduced as additions to the protocol without breaking backwards
 compatibility with earlier versions.
 OLSR does not require any changes to the format of IP packets.  Thus
 any existing IP stack can be used as is: the protocol only interacts
 with routing table management.

1.4. Multipoint Relays

 The idea of multipoint relays is to minimize the overhead of flooding
 messages in the network by reducing redundant retransmissions in the
 same region.  Each node in the network selects a set of nodes in its
 symmetric 1-hop neighborhood which may retransmit its messages.  This
 set of selected neighbor nodes is called the "Multipoint Relay" (MPR)
 set of that node.  The neighbors of node N which are *NOT* in its MPR
 set, receive and process broadcast messages but do not retransmit
 broadcast messages received from node N.
 Each node selects its MPR set from among its 1-hop symmetric
 neighbors.  This set is selected such that it covers (in terms of
 radio range) all symmetric strict 2-hop nodes.  The MPR set of N,
 denoted as MPR(N), is then an arbitrary subset of the symmetric 1-hop
 neighborhood of N which satisfies the following condition: every node
 in the symmetric strict 2-hop neighborhood of N must have a symmetric
 link towards MPR(N).  The smaller a MPR set, the less control traffic
 overhead results from the routing protocol.  [2] gives an analysis
 and example of MPR selection algorithms.
 Each node maintains information about the set of neighbors that have
 selected it as MPR.  This set is called the "Multipoint Relay
 Selector set" (MPR selector set) of a node.  A node obtains this
 information from periodic HELLO messages received from the neighbors.
 A broadcast message, intended to be diffused in the whole network,
 coming from any of the MPR selectors of node N is assumed to be
 retransmitted by node N, if N has not received it yet.  This set can
 change over time (i.e., when a node selects another MPR-set) and is
 indicated by the selector nodes in their HELLO messages.

2. Protocol Functioning

 This section outlines the overall protocol functioning.
 OLSR is modularized into a "core" of functionality, which is always
 required for the protocol to operate, and a set of auxiliary
 functions.

Clausen & Jacquet Experimental [Page 9] RFC 3626 Optimized Link State Routing October 2003

 The core specifies, in its own right, a protocol able to provide
 routing in a stand-alone MANET.
 Each auxiliary function provides additional functionality, which may
 be applicable in specific scenarios, e.g., in case a node is
 providing connectivity between the MANET and another routing domain.
 All auxiliary functions are compatible, to the extent where any
 (sub)set of auxiliary functions may be implemented with the core.
 Furthermore, the protocol allows heterogeneous nodes, i.e., nodes
 which implement different subsets of the auxiliary functions, to
 coexist in the network.
 The purpose of dividing the functioning of OLSR into a core
 functionality and a set of auxiliary functions is to provide a simple
 and easy-to-comprehend protocol, and to provide a way of only adding
 complexity where specific additional functionality is required.

2.1. Core Functioning

 The core functionality of OLSR specifies the behavior of a node,
 equipped with OLSR interfaces participating in the MANET and running
 OLSR as routing protocol.  This includes a universal specification of
 OLSR protocol messages and their transmission through the network, as
 well as link sensing, topology diffusion and route calculation.
 Specifically, the core is made up from the following components:
    Packet Format and Forwarding
       A universal specification of the packet format and an optimized
       flooding mechanism serves as the transport mechanism for all
       OLSR control traffic.
    Link Sensing
       Link Sensing is accomplished through periodic emission of HELLO
       messages over the interfaces through which connectivity is
       checked.  A separate HELLO message is generated for each
       interface and emitted in correspondence with the provisions in
       section 7.
       Resulting from Link Sensing is a local link set, describing
       links between "local interfaces" and "remote interfaces" -
       i.e., interfaces on neighbor nodes.

Clausen & Jacquet Experimental [Page 10] RFC 3626 Optimized Link State Routing October 2003

       If sufficient information is provided by the link-layer, this
       may be utilized to populate the local link set instead of HELLO
       message exchange.
    Neighbor detection
       Given a network with only single interface nodes, a node may
       deduct the neighbor set directly from the information exchanged
       as part of link sensing: the "main address" of a single
       interface node is, by definition, the address of the only
       interface on that node.
       In a network with multiple interface nodes, additional
       information is required in order to map interface addresses to
       main addresses (and, thereby, to nodes).  This additional
       information is acquired through multiple interface declaration
       (MID) messages, described in section 5.
    MPR Selection and MPR Signaling
       The objective of MPR selection is for a node to select a subset
       of its neighbors such that a broadcast message, retransmitted
       by these selected neighbors, will be received by all nodes 2
       hops away.  The MPR set of a node is computed such that it, for
       each interface, satisfies this condition.  The information
       required to perform this calculation is acquired through the
       periodic exchange of HELLO messages, as described in section 6.
       MPR selection procedures are detailed in section 8.3.
       MPR signaling is provided in correspondence with the provisions
       in the section 6.
    Topology Control Message Diffusion
       Topology Control messages are diffused with the purpose of
       providing each node in the network with sufficient link-state
       information to allow route calculation.  Topology Control
       messages are diffused in correspondence with the provisions in
       section 9.
    Route Calculation
       Given the link state information acquired through periodic
       message exchange, as well as the interface configuration of the
       nodes, the routing table for each node can be computed.  This
       is detailed in section 10.

Clausen & Jacquet Experimental [Page 11] RFC 3626 Optimized Link State Routing October 2003

 The key notion for these mechanisms is the MPR relationship.
 The following table specifies the component of the core functionality
 of OLSR, as well as their relations to this document.
        Feature                      |  Section
       ------------------------------+--------------
        Packet format and forwarding |     3
        Information repositories     |     4
        Main addr and multiple if.   |     5
        Hello messages               |     6
        Link sensing                 |     7
        Neighbor detection           |     8
        Topology discovery           |     9
        Routing table computation    |    10
        Node configuration           |    11

2.2. Auxiliary Functioning

 In addition to the core functioning of OLSR, there are situations
 where additional functionality is desired.  This includes situations
 where a node has multiple interfaces, some of which participate in
 another routing domain, where the programming interface to the
 networking hardware provides additional information in form of link
 layer notifications and where it is desired to provide redundant
 topological information to the network on expense of protocol
 overhead.
 The following table specifies auxiliary functions and their relation
 to this document.
        Feature                      |  Section
       ------------------------------+--------------
        Non-OLSR interfaces          |    12
        Link-layer notifications     |    13
        Advanced link sensing        |    14
        Redundant topology           |    15
        Redundant MPR flooding       |    16
 The interpretation of the above table is as follows: if the feature
 listed is required, it SHOULD be provided as specified in the
 corresponding section.

Clausen & Jacquet Experimental [Page 12] RFC 3626 Optimized Link State Routing October 2003

3. Packet Format and Forwarding

 OLSR communicates using a unified packet format for all data related
 to the protocol.  The purpose of this is to facilitate extensibility
 of the protocol without breaking backwards compatibility.  This also
 provides an easy way of piggybacking different "types" of information
 into a single transmission, and thus for a given implementation to
 optimize towards utilizing the maximal frame-size, provided by the
 network.  These packets are embedded in UDP datagrams for
 transmission over the network.  The present document is presented
 with IPv4 addresses.  Considerations regarding IPv6 are given in
 section 17.
 Each packet encapsulates one or more messages.  The messages share a
 common header format, which enables nodes to correctly accept and (if
 applicable) retransmit messages of an unknown type.
 Messages can be flooded onto the entire network, or flooding can be
 limited to nodes within a diameter (in terms of number of hops) from
 the originator of the message.  Thus transmitting a message to the
 neighborhood of a node is just a special case of flooding.  When
 flooding any control message, duplicate retransmissions will be
 eliminated locally (i.e., each node maintains a duplicate set to
 prevent transmitting the same OLSR control message twice) and
 minimized in the entire network through the usage of MPRs as
 described in later sections.
 Furthermore, a node can examine the header of a message to obtain
 information on the distance (in terms of number of hops) to the
 originator of the message.  This feature may be useful in situations
 where, e.g., the time information from a received control messages
 stored in a node depends on the distance to the originator.

3.1. Protocol and Port Number

 Packets in OLSR are communicated using UDP.  Port 698 has been
 assigned by IANA for exclusive usage by the OLSR protocol.

3.2. Main Address

 For a node with one interface, the main address of a node, as defined
 in "OLSR Terminology", MUST be set to the address of that interface.

Clausen & Jacquet Experimental [Page 13] RFC 3626 Optimized Link State Routing October 2003

3.3. Packet Format

 The basic layout of any packet in OLSR is as follows (omitting IP and
 UDP headers):
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Packet Length         |    Packet Sequence Number     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Message Type |     Vtime     |         Message Size          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Originator Address                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Time To Live |   Hop Count   |    Message Sequence Number    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    :                            MESSAGE                            :
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Message Type |     Vtime     |         Message Size          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Originator Address                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Time To Live |   Hop Count   |    Message Sequence Number    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    :                            MESSAGE                            :
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                                               :
             (etc.)

3.3.1. Packet Header

    Packet Length
       The length (in bytes) of the packet
    Packet Sequence Number
       The Packet Sequence Number (PSN) MUST be incremented by one
       each time a new OLSR packet is transmitted.  "Wrap-around" is
       handled as described in section 19.  A separate Packet Sequence
       Number is maintained for each interface such that packets
       transmitted over an interface are sequentially enumerated.

Clausen & Jacquet Experimental [Page 14] RFC 3626 Optimized Link State Routing October 2003

 The IP address of the interface over which a packet was transmitted
 is obtainable from the IP header of the packet.
 If the packet contains no messages (i.e., the Packet Length is less
 than or equal to the size of the packet header), the packet MUST
 silently be discarded.
 For IPv4 addresses, this implies that packets, where the Packet
 Length < 16 MUST silently be discarded.

3.3.2. Message Header

    Message Type
       This field indicates which type of message is to be found in
       the "MESSAGE" part.  Message types in the range of 0-127 are
       reserved for messages in this document and in possible
       extensions.
    Vtime
       This field indicates for how long time after reception a node
       MUST consider the information contained in the message as
       valid, unless a more recent update to the information is
       received.  The validity time is represented by its mantissa
       (four highest bits of Vtime field) and by its exponent (four
       lowest bits of Vtime field).  In other words:
            validity time = C*(1+a/16)* 2^b  [in seconds]
       where a is the integer represented by the four highest bits of
       Vtime field and b the integer represented by the four lowest
       bits of Vtime field.  The proposed value of the scaling factor
       C is specified in section 18.
    Message Size
       This gives the size of this message, counted in bytes and
       measured from the beginning of the "Message Type" field and
       until the beginning of the next "Message Type" field (or - if
       there are no following messages - until the end of the packet).
    Originator Address
       This field contains the main address of the node, which has
       originally generated this message.  This field SHOULD NOT be
       confused with the source address from the IP header, which is
       changed each time to the address of the intermediate interface

Clausen & Jacquet Experimental [Page 15] RFC 3626 Optimized Link State Routing October 2003

       which is re-transmitting this message.  The Originator Address
       field MUST *NEVER* be changed in retransmissions.
    Time To Live
       This field contains the maximum number of hops a message will
       be transmitted.  Before a message is retransmitted, the Time To
       Live MUST be decremented by 1.  When a node receives a message
       with a Time To Live equal to 0 or 1, the message MUST NOT be
       retransmitted under any circumstances.  Normally, a node would
       not receive a message with a TTL of zero.
       Thus, by setting this field, the originator of a message can
       limit the flooding radius.
    Hop Count
       This field contains the number of hops a message has attained.
       Before a message is retransmitted, the Hop Count MUST be
       incremented by 1.
       Initially, this is set to '0' by the originator of the message.
    Message Sequence Number
       While generating a message, the "originator" node will assign a
       unique identification number to each message.  This number is
       inserted into the Sequence Number field of the message.  The
       sequence number is increased by 1 (one) for each message
       originating from the node.  "Wrap-around" is handled as
       described in section 19.  Message sequence numbers are used to
       ensure that a given message is not retransmitted more than once
       by any node.

3.4. Packet Processing and Message Flooding

 Upon receiving a basic packet, a node examines each of the "message
 headers".  Based on the value of the "Message Type" field, the node
 can determine the fate of the message.  A node may receive the same
 message several times.  Thus, to avoid re-processing of some messages
 which were already received and processed, each node maintains a
 Duplicate Set.  In this set, the node records information about the
 most recently received messages where duplicate processing of a
 message is to be avoided.  For such a message, a node records a
 "Duplicate Tuple" (D_addr, D_seq_num, D_retransmitted, D_iface_list,
 D_time), where D_addr is the originator address of the message,
 D_seq_num is the message sequence number of the message,
 D_retransmitted is a boolean indicating whether the message has been

Clausen & Jacquet Experimental [Page 16] RFC 3626 Optimized Link State Routing October 2003

 already retransmitted, D_iface_list is a list of the addresses of the
 interfaces on which the message has been received and D_time
 specifies the time at which a tuple expires and *MUST* be removed.
 In a node, the set of Duplicate Tuples are denoted the "Duplicate
 set".
 In this section, the term "Originator Address" will be used for the
 main address of the node which sent the message.  The term "Sender
 Interface Address" will be used for the sender address (given in the
 IP header of the packet containing the message) of the interface
 which sent the message.  The term "Receiving Interface Address" will
 be used for the address of the interface of the node which received
 the message.
 Thus, upon receiving a basic packet, a node MUST perform the
 following tasks for each encapsulated message:
   1    If the packet contains no messages (i.e., the Packet Length is
        less than or equal to the size of the packet header), the
        packet MUST silently be discarded.
        For IPv4 addresses, this implies that packets, where the
        Packet Length < 16 MUST silently be discarded.
   2    If the time to live of the message is less than or equal to
        '0' (zero), or if the message was sent by the receiving node
        (i.e., the Originator Address of the message is the main
        address of the receiving node): the message MUST silently be
        dropped.
   3    Processing condition:
        3.1  if there exists a tuple in the duplicate set, where:
                           D_addr    == Originator Address, AND
                           D_seq_num == Message Sequence Number
             then the message has already been completely processed
             and MUST not be processed again.
        3.2  Otherwise, if the node implements the Message Type of the
             message, the message MUST be processed according to the
             specifications for the message type.

Clausen & Jacquet Experimental [Page 17] RFC 3626 Optimized Link State Routing October 2003

   4    Forwarding condition:
        4.1  if there exists a tuple in the duplicate set, where:
                              D_addr    == Originator Address, AND
                              D_seq_num == Message Sequence Number,
                  AND
                              the receiving interface (address) is
                              in D_iface_list
             then the message has already been considered for
             forwarding and SHOULD NOT be retransmitted again.
        4.2  Otherwise:
             4.2.1
                  If the node implements the Message Type of the
                  message, the message MUST be considered for
                  forwarding according to the specifications for
                  the message type.
             4.2.2
                  Otherwise, if the node does not implement the
                  Message Type of the message, the message SHOULD
                  be processed according to the default
                  forwarding algorithm described below.

3.4.1. Default Forwarding Algorithm

 The default forwarding algorithm is the following:
   1    If the sender interface address of the message is not detected
        to be in the symmetric 1-hop neighborhood of the node, the
        forwarding algorithm MUST silently stop here (and the message
        MUST NOT be forwarded).
   2    If there exists a tuple in the duplicate set where:
             D_addr    == Originator Address
             D_seq_num == Message Sequence Number
        Then the message will be further considered for forwarding if
        and only if:
             D_retransmitted is false, AND

Clausen & Jacquet Experimental [Page 18] RFC 3626 Optimized Link State Routing October 2003

             the (address of the) interface which received the message
             is not included among the addresses in D_iface_list
   3    Otherwise, if such an entry doesn't exist, the message is
        further considered for forwarding.
 If after those steps, the message is not considered for forwarding,
 then the processing of this section stops (i.e., steps 4 to 8 are
 ignored), otherwise, if it is still considered for forwarding then
 the following algorithm is used:
   4    If the sender interface address is an interface address of a
        MPR selector of this node and if the time to live of the
        message is greater than '1', the message MUST be retransmitted
        (as described later in steps 6 to 8).
   5    If an entry in the duplicate set exists, with same Originator
        Address, and same Message Sequence Number, the entry is
        updated as follows:
             D_time    = current time + DUP_HOLD_TIME.
             The receiving interface (address) is added to
             D_iface_list.
             D_retransmitted is set to true if and only if the message
             will be retransmitted according to step 4.
        Otherwise an entry in the duplicate set is recorded with:
             D_addr    = Originator Address
             D_seq_num = Message Sequence Number
             D_time    = current time + DUP_HOLD_TIME.
             D_iface_list contains the receiving interface address.
             D_retransmitted is set to true if and only if the message
             will be retransmitted according to step 4.
 If, and only if, according to step 4, the message must be
 retransmitted then:
   6    The TTL of the message is reduced by one.
   7    The hop-count of the message is increased by one

Clausen & Jacquet Experimental [Page 19] RFC 3626 Optimized Link State Routing October 2003

   8    The message is broadcast on all interfaces (Notice: The
        remaining fields of the message header SHOULD be left
        unmodified.)

3.4.2. Considerations on Processing and Forwarding

 It should be noted that processing and forwarding messages are two
 different actions, conditioned by different rules.  Processing
 relates to using the content of the messages, while forwarding is
 related to retransmitting the same message for other nodes of the
 network.
 Notice that this specification includes a description for both the
 forwarding and the processing of each known message type.  Messages
 with known message types MUST *NOT* be forwarded "blindly" by this
 algorithm.  Forwarding (and setting the correct message header in the
 forwarded, known, message) is the responsibility of the algorithm
 specifying how the message is to be handled and, if necessary,
 retransmitted.  This enables a message type to be specified such that
 the message can be modified while in transit (e.g., to reflect the
 route the message has taken).  It also enables bypassing of the MPR
 flooding mechanism if for some reason classical flooding of a message
 type is required, the algorithm which specifies how such messages
 should be handled will simply rebroadcast the message, regardless of
 MPRs.
 By defining a set of message types, which MUST be recognized by all
 implementations of OLSR, it will be possible to extend the protocol
 through introduction of additional message types, while still being
 able to maintain compatibility with older implementations.  The
 REQUIRED message types for the core functionality of OLSR are:
  1. HELLO-messages, performing the task of link sensing, neighbor

detection and MPR signaling,

  1. TC-messages, performing the task of topology declaration

(advertisement of link states).

  1. MID-messages, performing the task of declaring the presence of

multiple interfaces on a node.

 Other message types include those specified in later sections, as
 well as possible future extensions such as messages enabling power
 conservation / sleep mode, multicast routing, support for
 unidirectional links, auto-configuration/address assignment etc.

Clausen & Jacquet Experimental [Page 20] RFC 3626 Optimized Link State Routing October 2003

3.5. Message Emission and Jitter

 As a basic implementation requirement, synchronization of control
 messages SHOULD be avoided.  As a consequence, OLSR control messages
 SHOULD be emitted such that they avoid synchronization.
 Emission of control traffic from neighboring nodes may, for various
 reasons (mainly timer interactions with packet processing), become
 synchronized such that several neighbor nodes attempt to transmit
 control traffic simultaneously.  Depending on the nature of the
 underlying link-layer, this may or may not lead to collisions and
 hence message loss - possibly loss of several subsequent messages of
 the same type.
 To avoid such synchronizations, the following simple strategy for
 emitting control messages is proposed.  A node SHOULD add an amount
 of jitter to the interval at which messages are generated.  The
 jitter must be a random value for each message generated.  Thus, for
 a node utilizing jitter:
      Actual message interval = MESSAGE_INTERVAL - jitter
 Where jitter is a value, randomly selected from the interval
 [0,MAXJITTER] and MESSAGE_INTERVAL is the value of the message
 interval specified for the message being emitted (e.g.,
 HELLO_INTERVAL for HELLO messages, TC_INTERVAL for TC-messages etc.).
 Jitter SHOULD also be introduced when forwarding messages.  The
 following simple strategy may be adopted: when a message is to be
 forwarded by a node, it should be kept in the node during a short
 period of time :
         Keep message period = jitter
 Where jitter is a random value in [0,MAXJITTER].
 Notice that when the node sends a control message, the opportunity to
 piggyback other messages (before their keeping period is expired) may
 be taken to reduce the number of packet transmissions.
 Notice, that a minimal rate of control messages is imposed.  A node
 MAY send control messages at a higher rate, if beneficial for a
 specific deployment.

Clausen & Jacquet Experimental [Page 21] RFC 3626 Optimized Link State Routing October 2003

4. Information Repositories

 Through the exchange of OLSR control messages, each node accumulates
 information about the network.  This information is stored according
 to the descriptions in this section.

4.1. Multiple Interface Association Information Base

 For each destination in the network, "Interface Association Tuples"
 (I_iface_addr, I_main_addr, I_time) are recorded.  I_iface_addr is an
 interface address of a node, I_main_addr is the main address of this
 node.  I_time specifies the time at which this tuple expires and
 *MUST* be removed.
 In a node, the set of Interface Association Tuples is denoted the
 "Interface Association Set".

4.2. Link Sensing: Local Link Information Base

 The local link information base stores information about links to
 neighbors.

4.2.1. Link Set

 A node records a set of "Link Tuples" (L_local_iface_addr,
 L_neighbor_iface_addr, L_SYM_time, L_ASYM_time, L_time).
 L_local_iface_addr is the interface address of the local node (i.e.,
 one endpoint of the link), L_neighbor_iface_addr is the interface
 address of the neighbor node (i.e., the other endpoint of the link),
 L_SYM_time is the time until which the link is considered symmetric,
 L_ASYM_time is the time until which the neighbor interface is
 considered heard, and L_time specifies the time at which this record
 expires and *MUST* be removed.  When L_SYM_time and L_ASYM_time are
 expired, the link is considered lost.
 This information is used when declaring the neighbor interfaces in
 the HELLO messages.
 L_SYM_time is used to decide the Link Type declared for the neighbor
 interface.  If L_SYM_time is not expired, the link MUST be declared
 symmetric.  If L_SYM_time is expired, the link MUST be declared
 asymmetric.  If both L_SYM_time and L_ASYM_time are expired, the link
 MUST be declared lost.
 In a node, the set of Link Tuples are denoted the "Link Set".

Clausen & Jacquet Experimental [Page 22] RFC 3626 Optimized Link State Routing October 2003

4.3. Neighbor Detection: Neighborhood Information Base

 The neighborhood information base stores information about neighbors,
 2-hop neighbors, MPRs and MPR selectors.

4.3.1. Neighbor Set

 A node records a set of "neighbor tuples" (N_neighbor_main_addr,
 N_status, N_willingness), describing neighbors.  N_neighbor_main_addr
 is the main address of a neighbor, N_status specifies if the node is
 NOT_SYM or SYM.  N_willingness in an integer between 0 and 7, and
 specifies the node's willingness to carry traffic on behalf of other
 nodes.

4.3.2. 2-hop Neighbor Set

 A node records a set of "2-hop tuples" (N_neighbor_main_addr,
 N_2hop_addr, N_time), describing symmetric (and, since MPR links by
 definition are also symmetric, thereby also MPR) links between its
 neighbors and the symmetric 2-hop neighborhood.  N_neighbor_main_addr
 is the main address of a neighbor, N_2hop_addr is the main address of
 a 2-hop neighbor with a symmetric link to N_neighbor_main_addr, and
 N_time specifies the time at which the tuple expires and *MUST* be
 removed.
 In a node, the set of 2-hop tuples are denoted the "2-hop Neighbor
 Set".

4.3.3. MPR Set

 A node maintains a set of neighbors which are selected as MPR.  Their
 main addresses are listed in the MPR Set.

4.3.4. MPR Selector Set

 A node records a set of MPR-selector tuples (MS_main_addr, MS_time),
 describing the neighbors which have selected this node as a MPR.
 MS_main_addr is the main address of a node, which has selected this
 node as MPR.  MS_time specifies the time at which the tuple expires
 and *MUST* be removed.
 In a node, the set of MPR-selector tuples are denoted the "MPR
 Selector Set".

Clausen & Jacquet Experimental [Page 23] RFC 3626 Optimized Link State Routing October 2003

4.4. Topology Information Base

 Each node in the network maintains topology information about the
 network.  This information is acquired from TC-messages and is used
 for routing table calculations.
 Thus, for each destination in the network, at least one "Topology
 Tuple" (T_dest_addr, T_last_addr, T_seq, T_time) is recorded.
 T_dest_addr is the main address of a node, which may be reached in
 one hop from the node with the main address T_last_addr.  Typically,
 T_last_addr is a MPR of T_dest_addr.  T_seq is a sequence number, and
 T_time specifies the time at which this tuple expires and *MUST* be
 removed.
 In a node, the set of Topology Tuples are denoted the "Topology Set".

5. Main Addresses and Multiple Interfaces

 For single OLSR interface nodes, the relationship between an OLSR
 interface address and the corresponding main address is trivial: the
 main address is the OLSR interface address.  For multiple OLSR
 interface nodes, the relationship between OLSR interface addresses
 and main addresses is defined through the exchange of Multiple
 Interface Declaration (MID) messages.  This section describes how MID
 messages are exchanged and processed.
 Each node with multiple interfaces MUST announce, periodically,
 information describing its interface configuration to other nodes in
 the network.  This is accomplished through flooding a Multiple
 Interface Declaration message to all nodes in the network through the
 MPR flooding mechanism.
 Each node in the network maintains interface information about the
 other nodes in the network.  This information acquired from MID
 messages, emitted by nodes with multiple interfaces participating in
 the MANET, and is used for routing table calculations.
 Specifically, multiple interface declaration associates multiple
 interfaces to a node (and to a main address) through populating the
 multiple interface association base in each node.

Clausen & Jacquet Experimental [Page 24] RFC 3626 Optimized Link State Routing October 2003

5.1. MID Message Format

 The proposed format of a MID message is as follows:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    OLSR Interface Address                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    OLSR Interface Address                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              ...                              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 This is sent as the data-portion of the general packet format
 described in section 3.4, with the "Message Type" set to MID_MESSAGE.
 The time to live SHOULD be set to 255 (maximum value) to diffuse the
 message into the entire network and Vtime set accordingly to the
 value of MID_HOLD_TIME, as specified in section 18.3.
   OLSR Interface Address
        This field contains the address of an OLSR interface of the
        node, excluding the nodes main address (which already
        indicated in the originator address).
 All interface addresses other than the main address of the originator
 node are put in the MID message.  If the maximum allowed message size
 (as imposed by the network) is reached while there are still
 interface addresses which have not been inserted into the MIDmessage,
 more MID messages are generated until the entire interface addresses
 set has been sent.

5.2. MID Message Generation

 A MID message is sent by a node in the network to declare its
 multiple interfaces (if any).  I.e., the MID message contains the
 list of interface addresses which are associated to its main address.
 The list of addresses can be partial in each MID message (e.g., due
 to message size limitations, imposed by the network), but parsing of
 all MID messages describing the interface set from a node MUST be
 complete within a certain refreshing period (MID_INTERVAL).  The
 information diffused in the network by these MID messages will help
 each node to calculate its routing table.  A node which has only a
 single interface address participating in the MANET (i.e., running
 OLSR), MUST NOT generate any MID message.

Clausen & Jacquet Experimental [Page 25] RFC 3626 Optimized Link State Routing October 2003

 A node with several interfaces, where only one is participating in
 the MANET and running OLSR (e.g., a node is connected to a wired
 network as well as to a MANET) MUST NOT generate any MID messages.
 A node with several interfaces, where more than one is participating
 in the MANET and running OLSR MUST generate MID messages as
 specified.

5.3. MID Message Forwarding

 MID messages are broadcast and retransmitted by the MPRs in order to
 diffuse the messages in the entire network.  The "default forwarding
 algorithm" (described in section 3.4) MUST be used for forwarding of
 MID messages.

5.4. MID Message Processing

 The tuples in the multiple interface association set are recorded
 with the information that is exchanged through MID messages.
 Upon receiving a MID message, the "validity time" MUST be computed
 from the Vtime field of the message header (as described in section
 3.3.2).  The Multiple Interface Association Information Base SHOULD
 then be updated as follows:
   1    If the sender interface (NB: not originator) of this message
        is not in the symmetric 1-hop neighborhood of this node, the
        message MUST be discarded.
   2    For each interface address listed in the MID message:
        2.1  If there exist some tuple in the interface association
             set where:
                  I_iface_addr == interface address, AND
                  I_main_addr  == originator address,
             then the holding time of that tuple is set to:
                  I_time       = current time + validity time.
        2.2  Otherwise, a new tuple is recorded in the interface
             association set where:
                  I_iface_addr = interface address,
                  I_main_addr  = originator address,

Clausen & Jacquet Experimental [Page 26] RFC 3626 Optimized Link State Routing October 2003

                  I_time       = current time + validity time.

5.5. Resolving a Main Address from an Interface Address

 In general, the only part of OLSR requiring use of "interface
 addresses" is link sensing.  The remaining parts of OLSR operate on
 nodes, uniquely identified by their "main addresses" (effectively,
 the main address of a node is its "node id" - which for convenience
 corresponds to the address of one of its interfaces).  In a network
 with only single interface nodes, the main address of a node will, by
 definition, be equal to the interface address of the node.  In
 networks with multiple interface nodes operating within a common OLSR
 area, it is required to be able to map any interface address to the
 corresponding main address.
 The exchange of MID messages provides a way in which interface
 information is acquired by nodes in the network.  This permits
 identification of a node's "main address", given one of its interface
 addresses.
 Given an interface address:
   1    if there exists some tuple in the interface association set
        where:
             I_iface_addr == interface address
        then the result of the main address search is the originator
        address I_main_addr of the tuple.
   2    Otherwise, the result of the main address search is the
        interface address itself.

6. HELLO Message Format and Generation

 A common mechanism is employed for populating the local link
 information base and the neighborhood information base, namely
 periodic exchange of HELLO messages.  Thus this section describes the
 general HELLO message mechanism, followed by a description of link
 sensing and topology detection, respectively.

6.1. HELLO Message Format

 To accommodate for link sensing, neighborhood detection and MPR
 selection signalling, as well as to accommodate for future
 extensions, an approach similar to the overall packet format is
 taken.  Thus the proposed format of a HELLO message is as follows:

Clausen & Jacquet Experimental [Page 27] RFC 3626 Optimized Link State Routing October 2003

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Reserved             |     Htime     |  Willingness  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Link Code   |   Reserved    |       Link Message Size       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Neighbor Interface Address                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Neighbor Interface Address                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                             .  .  .                           :
    :                                                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Link Code   |   Reserved    |       Link Message Size       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Neighbor Interface Address                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Neighbor Interface Address                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                                               :
    :                                       :
 (etc.)
 This is sent as the data-portion of the general packet format
 described in section 3.4, with the "Message Type" set to
 HELLO_MESSAGE, the TTL field set to 1 (one) and Vtime set accordingly
 to the value of NEIGHB_HOLD_TIME, specified in section 18.3.
    Reserved
       This field must be set to "0000000000000" to be in compliance
       with this specification.
    HTime
       This field specifies the HELLO emission interval used by the
       node on this particular interface, i.e., the time before the
       transmission of the next HELLO (this information may be used in
       advanced link sensing, see section 14).  The HELLO emission
       interval is represented by its mantissa (four highest bits of
       Htime field) and by its exponent (four lowest bits of Htime
       field).  In other words:
            HELLO emission interval=C*(1+a/16)*2^b  [in seconds]

Clausen & Jacquet Experimental [Page 28] RFC 3626 Optimized Link State Routing October 2003

       where a is the integer represented by the four highest bits of
       Htime field and b the integer represented by the four lowest
       bits of Htime field.  The proposed value of the scaling factor
       C is specified in section 18.
    Willingness
       This field specifies the willingness of a node to carry and
       forward traffic for other nodes.
       A node with willingness WILL_NEVER (see section 18.8, for
       willingness constants) MUST never be selected as MPR by any
       node.  A node with willingness WILL_ALWAYS MUST always be
       selected as MPR.  By default, a node SHOULD advertise a
       willingness of WILL_DEFAULT.
    Link Code
       This field specifies information about the link between the
       interface of the sender and the following list of neighbor
       interfaces.  It also specifies information about the status of
       the neighbor.
       Link codes, not known by a node, are silently discarded.
    Link Message Size
       The size of the link message, counted in bytes and measured
       from the beginning of the "Link Code" field and until the next
       "Link Code" field (or - if there are no more link types - the
       end of the message).
    Neighbor Interface Address
       The address of an interface of a neighbor node.

6.1.1. Link Code as Link Type and Neighbor Type

 This document only specifies processing of Link Codes < 16.
 If the Link Code value is less than or equal to 15, then it MUST be
 interpreted as holding two different fields, of two bits each:
        7       6       5       4       3       2       1       0
    +-------+-------+-------+-------+-------+-------+-------+-------+
    |   0   |   0   |   0   |   0   | Neighbor Type |   Link Type   |
    +-------+-------+-------+-------+-------+-------+-------+-------+

Clausen & Jacquet Experimental [Page 29] RFC 3626 Optimized Link State Routing October 2003

 The following four "Link Types" are REQUIRED by OLSR:
  1. UNSPEC_LINK - indicating that no specific information about

the links is given.

  1. ASYM_LINK - indicating that the links are asymmetric (i.e.,

the neighbor interface is "heard").

  1. SYM_LINK - indicating that the links are symmetric with the

interface.

  1. LOST_LINK - indicating that the links have been lost.
 The following three "Neighbor Types" are REQUIRED by OLSR:
  1. SYM_NEIGH - indicating that the neighbors have at least one

symmetrical link with this node.

  1. MPR_NEIGH - indicating that the neighbors have at least one

symmetrical link AND have been selected as MPR by the sender.

  1. NOT_NEIGH - indicating that the nodes are either no longer or

have not yet become symmetric neighbors.

 Note that an implementation should be careful in confusing neither
 Link Type with Neighbor Type nor the constants (confusing SYM_NEIGH
 with SYM_LINK for instance).
 A link code advertising:
        Link Type     == SYM_LINK AND
        Neighbor Type == NOT_NEIGH
 is invalid, and any links advertised as such MUST be silently
 discarded without any processing.
 Likewise a Neighbor Type field advertising a numerical value which is
 not one of the constants SYM_NEIGH, MPR_NEIGH, NOT_NEIGH, is invalid,
 and any links advertised as such MUST be silently discarded without
 any processing.

6.2. HELLO Message Generation

 This involves transmitting the Link Set, the Neighbor Set and the MPR
 Set.  In principle, a HELLO message serves three independent tasks:
  1. link sensing

Clausen & Jacquet Experimental [Page 30] RFC 3626 Optimized Link State Routing October 2003

  1. neighbor detection
  1. MPR selection signaling
 Three tasks are all are based on periodic information exchange within
 a nodes neighborhood, and serve the common purpose of "local topology
 discovery".  A HELLO message is therefore generated based on the
 information stored in the Local Link Set, the Neighbor Set and the
 MPR Set from the local link information base.
 A node must perform link sensing on each interface, in order to
 detect links between the interface and neighbor interfaces.
 Furthermore, a node must advertise its entire symmetric 1-hop
 neighborhood on each interface in order to perform neighbor
 detection.  Hence, for a given interface, a HELLO message will
 contain a list of links on that interface (with associated link
 types), as well as a list of the entire neighborhood (with an
 associated neighbor types).
 The Vtime field is set such that it corresponds to the value of the
 node's NEIGHB_HOLD_TIME parameter.  The Htime field is set such that
 it corresponds to the value of the node's HELLO_INTERVAL parameter
 (see section 18.3).
 The Willingness field is set such that it corresponds to the node's
 willingness to forward traffic on behalf of other nodes (see section
 18.8).  A node MUST advertise the same willingness on all interfaces.
 The lists of addresses declared in a HELLO message is a list of
 neighbor interface addresses computed as follows:
 For each tuple in the Link Set, where L_local_iface_addr is the
 interface where the HELLO is to be transmitted, and where L_time >=
 current time (i.e., not expired), L_neighbor_iface_addr is advertised
 with:
   1    The Link Type set according to the following:
        1.1  if L_SYM_time >= current time (not expired)
                  Link Type = SYM_LINK
        1.2  Otherwise, if L_ASYM_time >= current time (not expired)
             AND
                           L_SYM_time  <  current time (expired)
                  Link Type = ASYM_LINK

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        1.3  Otherwise, if L_ASYM_time < current time (expired) AND
                           L_SYM_time  < current time (expired)
                  Link Type = LOST_LINK
   2    The Neighbor Type is set according to the following:
        2.1  If the main address, corresponding to
             L_neighbor_iface_addr, is included in the MPR set:
                  Neighbor Type = MPR_NEIGH
        2.2  Otherwise, if the main address, corresponding to
             L_neighbor_iface_addr, is included in the neighbor set:
             2.2.1
                  if N_status == SYM
                       Neighbor Type = SYM_NEIGH
             2.2.2
                  Otherwise, if N_status == NOT_SYM
                       Neighbor Type = NOT_NEIGH
 For each tuple in the Neighbor Set, for which no
 L_neighbor_iface_addr from an associated link tuple has been
 advertised by the previous algorithm,  N_neighbor_main_addr is
 advertised with:
  1. Link Type = UNSPEC_LINK,
  1. Neighbor Type set as described in step 2 above
 For a node with a single OLSR interface, the main address is simply
 the address of the OLSR interface, i.e., for a node with a single
 OLSR interface the main address, corresponding to
 L_neighbor_iface_addr is simply L_neighbor_iface_addr.
 A HELLO message can be partial (e.g., due to message size
 limitations, imposed by the network), the rule being the following,
 on each interface: each link and each neighbor node MUST be cited at
 least once within a predetermined refreshing period,
 REFRESH_INTERVAL.  To keep track of fast connectivity changes, a
 HELLO message must be sent at least every HELLO_INTERVAL period,
 smaller than or equal to REFRESH_INTERVAL.

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 Notice that for limiting the impact from loss of control messages, it
 is desirable that a message (plus the generic packet header) can fit
 into a single MAC frame.

6.3. HELLO Message Forwarding

 Each HELLO message generated is broadcast by the node on one
 interface to its neighbors (i.e. the interface for which the HELLO
 was generated).  HELLO messages MUST never be forwarded.

6.4. HELLO Message Processing

 A node processes incoming HELLO messages for the purpose of
 conducting link sensing (detailed in section 7), neighbor detection
 and MPR selector set population (detailed in section 8)

7. Link Sensing

 Link sensing populates the local link information base.  Link sensing
 is exclusively concerned with OLSR interface addresses and the
 ability to exchange packets between such OLSR interfaces.
 The mechanism for link sensing is the periodic exchange of HELLO
 messages.

7.1. Populating the Link Set

 The Link Set is populated with information on links to neighbor
 nodes.  The process of populating this set is denoted "link sensing"
 and is performed using HELLO message exchange, updating a local link
 information base in each node.
 Each node should detect the links between itself and neighbor nodes.
 Uncertainties over radio propagation may make some links
 unidirectional.  Consequently, all links MUST be checked in both
 directions in order to be considered valid.
 A "link" is described by a pair of interfaces: a local and a remote
 interface.
 For the purpose of link sensing, each neighbor node (more
 specifically, the link to each neighbor) has an associated status of
 either "symmetric" or "asymmetric".  "Symmetric" indicates, that the
 link to that neighbor node has been verified to be bi-directional,
 i.e., it is possible to transmit data in both directions.
 "Asymmetric" indicates that HELLO messages from the node have been

Clausen & Jacquet Experimental [Page 33] RFC 3626 Optimized Link State Routing October 2003

 heard (i.e., communication from the neighbor node is possible),
 however it is not confirmed that this node is also able to receive
 messages (i.e., communication to the neighbor node is not confirmed).
 The information, acquired through and used by the link sensing, is
 accumulated in the link set.

7.1.1. HELLO Message Processing

 The "Originator Address" of a HELLO message is the main address of
 the node, which has emitted the message.
 Upon receiving a HELLO message, a node SHOULD update its Link Set.
 Notice, that a HELLO message MUST neither be forwarded nor be
 recorded in the duplicate set.
 Upon receiving a HELLO message, the "validity time" MUST be computed
 from the Vtime field of the message header (see section 3.3.2).
 Then, the Link Set SHOULD be updated as follows:
   1    Upon receiving a HELLO message, if there exists no link tuple
        with
             L_neighbor_iface_addr == Source Address
        a new tuple is created with
             L_neighbor_iface_addr = Source Address
             L_local_iface_addr    = Address of the interface
                                     which received the
                                     HELLO message
             L_SYM_time            = current time - 1 (expired)
             L_time                = current time + validity time
   2    The tuple (existing or new) with:
             L_neighbor_iface_addr == Source Address
        is then modified as follows:
        2.1  L_ASYM_time = current time + validity time;
        2.2  if the node finds the address of the interface which
             received the HELLO message among the addresses listed in
             the link message then the tuple is modified as follows:

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             2.2.1
                  if Link Type is equal to LOST_LINK then
                       L_SYM_time = current time - 1 (i.e., expired)
             2.2.2
                  else if Link Type is equal to SYM_LINK or ASYM_LINK
                  then
                       L_SYM_time = current time + validity time,
                       L_time     = L_SYM_time + NEIGHB_HOLD_TIME
        2.3  L_time = max(L_time, L_ASYM_time)
 The above rule for setting L_time is the following: a link losing its
 symmetry SHOULD still be advertised during at least the duration of
 the "validity time" advertised in the generated HELLO.  This allows
 neighbors to detect the link breakage.

8. Neighbor Detection

 Neighbor detection populates the neighborhood information base and
 concerns itself with nodes and node main addresses.  The relationship
 between OLSR interface addresses and main addresses is described in
 section 5.
 The mechanism for neighbor detection is the periodic exchange of
 HELLO messages.

8.1. Populating the Neighbor Set

 A node maintains a set of neighbor tuples, based on the link tuples.
 This information is updated according to changes in the Link Set.
 The Link Set keeps the information about the links, while the
 Neighbor Set keeps the information about the neighbors.  There is a
 clear association between those two sets, since a node is a neighbor
 of another node if and only if there is at least one link between the
 two nodes.
 In any case, the formal correspondence between links and neighbors is
 defined as follows:
        The "associated neighbor tuple" of a link tuple, is, if it
        exists, the neighbor tuple where:

Clausen & Jacquet Experimental [Page 35] RFC 3626 Optimized Link State Routing October 2003

             N_neighbor_main_addr == main address of
                                     L_neighbor_iface_addr
        The "associated link tuples" of a neighbor tuple, are all the
        link tuples, where:
             N_neighbor_main_addr == main address of
                                     L_neighbor_iface_addr
 The Neighbor Set MUST be populated by maintaining the proper
 correspondence between link tuples and associated neighbor tuples, as
 follows:
   Creation
        Each time a link appears, that is, each time a link tuple is
        created, the associated neighbor tuple MUST be created, if it
        doesn't already exist, with the following values:
             N_neighbor_main_addr = main address of
                                    L_neighbor_iface_addr
                                    (from the link tuple)
        In any case, the N_status MUST then be computed as described
        in the next step
   Update
        Each time a link changes, that is, each time the information
        of a link tuple is modified, the node MUST ensure that the
        N_status of the associated neighbor tuple respects the
        property:
             If the neighbor has any associated link tuple which
             indicates a symmetric link (i.e., with L_SYM_time >=
             current time), then
                  N_status is set to SYM
             else N_status is set to NOT_SYM
   Removal
        Each time a link is deleted, that is, each time a link tuple
        is removed, the associated neighbor tuple MUST be removed if
        it has no longer any associated link tuples.

Clausen & Jacquet Experimental [Page 36] RFC 3626 Optimized Link State Routing October 2003

 These rules ensure that there is exactly one associated neighbor
 tuple for a link tuple, and that every neighbor tuple has at least
 one associated link tuple.

8.1.1. HELLO Message Processing

 The "Originator Address" of a HELLO message is the main address of
 the node, which has emitted the message.  Likewise, the "willingness"
 MUST be computed from the Willingness field of the HELLO message (see
 section 6.1).
 Upon receiving a HELLO message, a node SHOULD first update its Link
 Set as described before.  It SHOULD then update its Neighbor Set as
 follows:
  1. if the Originator Address is the N_neighbor_main_addr from a

neighbor tuple included in the Neighbor Set:

             then, the neighbor tuple SHOULD be updated as follows:
             N_willingness = willingness from the HELLO message

8.2. Populating the 2-hop Neighbor Set

 The 2-hop neighbor set describes the set of nodes which have a
 symmetric link to a symmetric neighbor.  This information set is
 maintained through periodic exchange of HELLO messages as described
 in this section.

8.2.1. HELLO Message Processing

 The "Originator Address" of a HELLO message is the main address of
 the node, which has emitted the message.
 Upon receiving a HELLO message from a symmetric neighbor, a node
 SHOULD update its 2-hop Neighbor Set.  Notice, that a HELLO message
 MUST neither be forwarded nor be recorded in the duplicate set.
 Upon receiving a HELLO message, the "validity time" MUST be computed
 from the Vtime field of the message header (see section 3.3.2).
 If the Originator Address is the main address of a
 L_neighbor_iface_addr from a link tuple included in the Link Set with
        L_SYM_time >= current time (not expired)
 (in other words: if the Originator Address is a symmetric neighbor)
 then the 2-hop Neighbor Set SHOULD be updated as follows:

Clausen & Jacquet Experimental [Page 37] RFC 3626 Optimized Link State Routing October 2003

   1    for each address (henceforth: 2-hop neighbor address), listed
        in the HELLO message with Neighbor Type equal to SYM_NEIGH or
        MPR_NEIGH:
        1.1  if the main address of the 2-hop neighbor address = main
             address of the receiving node:
                  silently discard the 2-hop neighbor address.
             (in other words: a node is not its own 2-hop neighbor).
        1.2  Otherwise, a 2-hop tuple is created with:
                  N_neighbor_main_addr =  Originator Address;
                  N_2hop_addr          =  main address of the
                                          2-hop neighbor;
                  N_time               =  current time
                                          + validity time.
             This tuple may replace an older similar tuple with same
             N_neighbor_main_addr and N_2hop_addr values.
   2    For each 2-hop node listed in the HELLO message with Neighbor
        Type equal to NOT_NEIGH, all 2-hop tuples where:
             N_neighbor_main_addr == Originator Address AND
             N_2hop_addr          == main address of the
                                     2-hop neighbor
        are deleted.

8.3. Populating the MPR set

 MPRs are used to flood control messages from a node into the network
 while reducing the number of retransmissions that will occur in a
 region.  Thus, the concept of MPR is an optimization of a classical
 flooding mechanism.
 Each node in the network selects, independently, its own set of MPRs
 among its symmetric 1-hop neighborhood.  The symmetric links with
 MPRs are advertised with Link Type MPR_NEIGH instead of SYM_NEIGH in
 HELLO messages.

Clausen & Jacquet Experimental [Page 38] RFC 3626 Optimized Link State Routing October 2003

 The MPR set MUST be calculated by a node in such a way that it,
 through the neighbors in the MPR-set, can reach all symmetric strict
 2-hop neighbors.  (Notice that a node, a, which is a direct neighbor
 of another node, b, is not also a strict 2-hop neighbor of node b).
 This means that the union of the symmetric 1-hop neighborhoods of the
 MPR nodes contains the symmetric strict 2-hop neighborhood.  MPR set
 recalculation should occur when changes are detected in the symmetric
 neighborhood or in the symmetric strict 2-hop neighborhood.
 MPRs are computed per interface, the union of the MPR sets of each
 interface make up the MPR set for the node.
 While it is not essential that the MPR set is minimal, it is
 essential that all strict 2-hop neighbors can be reached through the
 selected MPR nodes.  A node SHOULD select an MPR set such that any
 strict 2-hop neighbor is covered by at least one MPR node.  Keeping
 the MPR set small ensures that the overhead of the protocol is kept
 at a minimum.
 The MPR set can coincide with the entire symmetric neighbor set.
 This could be the case at network initialization (and will correspond
 to classic link-state routing).

8.3.1. MPR Computation

 The following specifies a proposed heuristic for selection of MPRs.
 It constructs an MPR-set that enables a node to reach any node in the
 symmetrical strict 2-hop neighborhood through relaying by one MPR
 node with willingness different from WILL_NEVER.  The heuristic MUST
 be applied per interface, I.  The MPR set for a node is the union of
 the MPR sets found for each interface.  The following terminology
 will be used in describing the heuristics:
     neighbor of an interface
            a node is a "neighbor of an interface" if the interface
            (on the local node) has a link to any one interface of
            the neighbor node.
     2-hop neighbors reachable from an interface
            the list of 2-hop neighbors of the node that can be
            reached from neighbors of this interface.

Clausen & Jacquet Experimental [Page 39] RFC 3626 Optimized Link State Routing October 2003

     MPR set of an interface
            a (sub)set of the neighbors of an interface with a
            willingness different from WILL_NEVER, selected such that
            through these selected nodes, all strict 2-hop neighbors
            reachable from that interface are reachable.
     N:
            N is the subset of neighbors of the node, which are
            neighbor of the interface I.
     N2:
            The set of 2-hop neighbors reachable from the interface
            I, excluding:
             (i)   the nodes only reachable by members of N with
                   willingness WILL_NEVER
             (ii)  the node performing the computation
             (iii) all the symmetric neighbors: the nodes for which
                   there exists a symmetric link to this node on some
                   interface.
  D(y):
            The degree of a 1-hop neighbor node y (where y is a
            member of N), is defined as the number of symmetric
            neighbors of node y, EXCLUDING all the members of N and
            EXCLUDING the node performing the computation.
 The proposed heuristic is as follows:
   1    Start with an MPR set made of all members of N with
        N_willingness equal to WILL_ALWAYS
   2    Calculate D(y), where y is a member of N, for all nodes in N.
   3    Add to the MPR set those nodes in N, which are the *only*
        nodes to provide reachability to a node in N2.  For example,
        if node b in N2 can be reached only through a symmetric link
        to node a in N, then add node a to the MPR set.  Remove the
        nodes from N2 which are now covered by a node in the MPR set.
   4    While there exist nodes in N2 which are not covered by at
        least one node in the MPR set:

Clausen & Jacquet Experimental [Page 40] RFC 3626 Optimized Link State Routing October 2003

        4.1  For each node in N, calculate the reachability, i.e., the
             number of nodes in N2 which are not yet covered by at
             least one node in the MPR set, and which are reachable
             through this 1-hop neighbor;
        4.2  Select as a MPR the node with highest N_willingness among
             the nodes in N with non-zero reachability.  In case of
             multiple choice select the node which provides
             reachability to the maximum number of nodes in N2.  In
             case of multiple nodes providing the same amount of
             reachability, select the node as MPR whose D(y) is
             greater.  Remove the nodes from N2 which are now covered
             by a node in the MPR set.
   5    A node's MPR set is generated from the union of the MPR sets
        for each interface.  As an optimization, process each node, y,
        in the MPR set in increasing order of N_willingness.  If all
        nodes in N2 are still covered by at least one node in the MPR
        set excluding node y, and if N_willingness of node y is
        smaller than WILL_ALWAYS, then node y MAY be removed from the
        MPR set.
 Other algorithms, as well as improvements over this algorithm, are
 possible.  For example, assume that in a multiple-interface scenario
 there exists more than one link between nodes 'a' and 'b'.  If node
 'a' has selected node 'b' as MPR for one of its interfaces, then node
 'b' can be selected as MPR without additional performance loss by any
 other interfaces on node 'a'.

8.4. Populating the MPR Selector Set

 The MPR selector set of a node, n, is populated by the main addresses
 of the nodes which have selected n as MPR.  MPR selection is signaled
 through HELLO messages.

8.4.1. HELLO Message Processing

 Upon receiving a HELLO message, if a node finds one of its own
 interface addresses in the list with a Neighbor Type equal to
 MPR_NEIGH, information from the HELLO message must be recorded in the
 MPR Selector Set.
 The "validity time" MUST be computed from the Vtime field of the
 message header (see section 3.3.2).  The MPR Selector Set SHOULD then
 be updated as follows:

Clausen & Jacquet Experimental [Page 41] RFC 3626 Optimized Link State Routing October 2003

   1    If there exists no MPR selector tuple with:
                  MS_main_addr   == Originator Address
             then a new tuple is created with:
                  MS_main_addr   =  Originator Address
   2    The tuple (new or otherwise) with
             MS_main_addr   == Originator Address
        is then modified as follows:
             MS_time        =  current time + validity time.
 Deletion of MPR selector tuples occurs in case of expiration of the
 timer or in case of link breakage as described in the "Neighborhood
 and 2-hop Neighborhood Changes".

8.5. Neighborhood and 2-hop Neighborhood Changes

 A change in the neighborhood is detected when:
  1. The L_SYM_time field of a link tuple expires. This is

considered as a neighbor loss if the link described by the

        expired tuple was the last link with a neighbor node (on the
        contrary, a link with an interface may break while a link with
        another interface of the neighbor node remains without being
        observed as a neighborhood change).
  1. A new link tuple is inserted in the Link Set with a non

expired L_SYM_time or a tuple with expired L_SYM_time is

        modified so that L_SYM_time becomes non-expired.  This is
        considered as a neighbor appearance if there was previously no
        link tuple describing a link with the corresponding neighbor
        node.
 A change in the 2-hop neighborhood is detected when a 2-hop neighbor
 tuple expires or is deleted according to section 8.2.
 The following processing occurs when changes in the neighborhood or
 the 2-hop neighborhood are detected:
  1. In case of neighbor loss, all 2-hop tuples with

N_neighbor_main_addr == Main Address of the neighbor MUST be

        deleted.

Clausen & Jacquet Experimental [Page 42] RFC 3626 Optimized Link State Routing October 2003

  1. In case of neighbor loss, all MPR selector tuples with

MS_main_addr == Main Address of the neighbor MUST be deleted

  1. The MPR set MUST be re-calculated when a neighbor appearance

or loss is detected, or when a change in the 2-hop

        neighborhood is detected.
  1. An additional HELLO message MAY be sent when the MPR set

changes.

9. Topology Discovery

 The link sensing and neighbor detection part of the protocol
 basically offers, to each node, a list of neighbors with which it can
 communicate directly and, in combination with the Packet Format and
 Forwarding part, an optimized flooding mechanism through MPRs.  Based
 on this, topology information is disseminated through the network.
 The present section describes which part of the information given by
 the link sensing and neighbor detection is disseminated to the entire
 network and how it is used to construct routes.
 Routes are constructed through advertised links and links with
 neighbors.  A node must at least disseminate links between itself and
 the nodes in its MPR-selector set, in order to provide sufficient
 information to enable routing.

9.1. TC Message Format

 The proposed format of a TC message is as follows:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              ANSN             |           Reserved            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               Advertised Neighbor Main Address                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               Advertised Neighbor Main Address                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              ...                              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 This is sent as the data-portion of the general message format with
 the "Message Type" set to TC_MESSAGE.  The time to live SHOULD be set
 to 255 (maximum value) to diffuse the message into the entire network
 and Vtime set accordingly to the value of TOP_HOLD_TIME, as specified
 in section 18.3.

Clausen & Jacquet Experimental [Page 43] RFC 3626 Optimized Link State Routing October 2003

   Advertised Neighbor Sequence Number (ANSN)
        A sequence number is associated with the advertised neighbor
        set.  Every time a node detects a change in its advertised
        neighbor set, it increments this sequence number ("Wraparound"
        is handled as described in section 19).  This number is sent
        in this ANSN field of the TC message to keep track of the most
        recent information.  When a node receives a TC message, it can
        decide on the basis of this Advertised Neighbor Sequence
        Number, whether or not the received information about the
        advertised neighbors of the originator node is more recent
        than what it already has.
   Advertised Neighbor Main Address
        This field contains the main address of a neighbor node.  All
        main addresses of the advertised neighbors of the Originator
        node are put in the TC message.  If the maximum allowed
        message size (as imposed by the network) is reached while
        there are still advertised neighbor addresses which have not
        been inserted into the TC-message, more TC messages will be
        generated until the entire advertised neighbor set has been
        sent.  Extra main addresses of neighbor nodes may be included,
        if redundancy is desired.
   Reserved
        This field is reserved, and MUST be set to "0000000000000000"
        for compliance with this document.

9.2. Advertised Neighbor Set

 A TC message is sent by a node in the network to declare a set of
 links, called advertised link set which MUST include at least the
 links to all nodes of its MPR Selector set, i.e., the neighbors which
 have selected the sender node as a MPR.
 If, for some reason, it is required to distribute redundant TC
 information, refer to section 15.
 The sequence number (ANSN) associated with the advertised neighbor
 set is also sent with the list.  The ANSN number MUST be incremented
 when links are removed from the advertised neighbor set; the ANSN
 number SHOULD be incremented when links are added to the advertised
 neighbor set.

Clausen & Jacquet Experimental [Page 44] RFC 3626 Optimized Link State Routing October 2003

9.3. TC Message Generation

 In order to build the topology information base, each node, which has
 been selected as MPR, broadcasts Topology Control (TC) messages.  TC
 messages are flooded to all nodes in the network and take advantage
 of MPRs.  MPRs enable a better scalability in the distribution of
 topology information [1].
 The list of addresses can be partial in each TC message (e.g., due to
 message size limitations, imposed by the network), but parsing of all
 TC messages describing the advertised link set of a node MUST be
 complete within a certain refreshing period (TC_INTERVAL).  The
 information diffused in the network by these TC messages will help
 each node calculate its routing table.
 When the advertised link set of a node becomes empty, this node
 SHOULD still send (empty) TC-messages during the a duration equal to
 the "validity time" (typically, this will be equal to TOP_HOLD_TIME)
 of its previously emitted TC-messages, in order to invalidate the
 previous TC-messages.  It SHOULD then stop sending TC-messages until
 some node is inserted in its advertised link set.
 A node MAY transmit additional TC-messages to increase its
 reactiveness to link failures.  When a change to the MPR selector set
 is detected and this change can be attributed to a link failure, a
 TC-message SHOULD be transmitted after an interval shorter than
 TC_INTERVAL.

9.4. TC Message Forwarding

 TC messages are broadcast and retransmitted by the MPRs in order to
 diffuse the messages in the entire network.  TC messages MUST be
 forwarded according to the "default forwarding algorithm" (described
 in section 3.4).

9.5. TC Message Processing

 Upon receiving a TC message, the "validity time" MUST be computed
 from the Vtime field of the message header (see section 3.3.2).  The
 topology set SHOULD then be updated as follows (using section 19 for
 comparison of ANSN):
   1    If the sender interface (NB: not originator) of this message
        is not in the symmetric 1-hop neighborhood of this node, the
        message MUST be discarded.

Clausen & Jacquet Experimental [Page 45] RFC 3626 Optimized Link State Routing October 2003

   2    If there exist some tuple in the topology set where:
             T_last_addr == originator address AND
             T_seq       >  ANSN,
        then further processing of this TC message MUST NOT be
        performed and the message MUST be silently discarded (case:
        message received out of order).
   3    All tuples in the topology set where:
             T_last_addr == originator address AND
             T_seq       <  ANSN
        MUST be removed from the topology set.
   4    For each of the advertised neighbor main address received in
        the TC message:
        4.1  If there exist some tuple in the topology set where:
                  T_dest_addr == advertised neighbor main address, AND
                  T_last_addr == originator address,
             then the holding time of that tuple MUST be set to:
                  T_time      =  current time + validity time.
        4.2  Otherwise, a new tuple MUST be recorded in the topology
             set where:
                  T_dest_addr = advertised neighbor main address,
                  T_last_addr = originator address,
                  T_seq       = ANSN,
                  T_time      = current time + validity time.

Clausen & Jacquet Experimental [Page 46] RFC 3626 Optimized Link State Routing October 2003

10. Routing Table Calculation

 Each node maintains a routing table which allows it to route data,
 destined for the other nodes in the network.  The routing table is
 based on the information contained in the local link information base
 and the topology set.  Therefore, if any of these sets are changed,
 the routing table is recalculated to update the route information
 about each destination in the network.  The route entries are
 recorded in the routing table in the following format:
       1.  R_dest_addr    R_next_addr    R_dist   R_iface_addr
       2.  R_dest_addr    R_next_addr    R_dist   R_iface_addr
       3.      ,,             ,,           ,,          ,,
 Each entry in the table consists of R_dest_addr, R_next_addr, R_dist,
 and R_iface_addr.  Such entry specifies that the node identified by
 R_dest_addr is estimated to be R_dist hops away from the local node,
 that the symmetric neighbor node with interface address R_next_addr
 is the next hop node in the route to R_dest_addr, and that this
 symmetric neighbor node is reachable through the local interface with
 the address R_iface_addr.  Entries are recorded in the routing table
 for each destination in the network for which a route is known.  All
 the destinations, for which a route is broken or only partially
 known, are not recorded in the table.
 More precisely, the routing table is updated when a change is
 detected in either:
  1. the link set,
  1. the neighbor set,
  1. the 2-hop neighbor set,
  1. the topology set,
  1. the Multiple Interface Association Information Base,
 More precisely, the routing table is recalculated in case of neighbor
 appearance or loss, when a 2-hop tuple is created or removed, when a
 topology tuple is created or removed or when multiple interface
 association information changes.  The update of this routing
 information does not generate or trigger any messages to be
 transmitted, neither in the network, nor in the 1-hop neighborhood.
 To construct the routing table of node X, a shortest path algorithm
 is run on the directed graph containing the arcs X -> Y where Y is
 any symmetric neighbor of X (with Neighbor Type equal to SYM), the

Clausen & Jacquet Experimental [Page 47] RFC 3626 Optimized Link State Routing October 2003

 arcs Y -> Z where Y is a neighbor node with willingness different of
 WILL_NEVER and there exists an entry in the 2-hop Neighbor set with Y
 as N_neighbor_main_addr and Z as N_2hop_addr, and the arcs U -> V,
 where there exists an entry in the topology set with V as T_dest_addr
 and U as T_last_addr.
 The following procedure is given as an example to calculate (or
 recalculate) the routing table:
   1    All the entries from the routing table are removed.
   2    The new routing entries are added starting with the
        symmetric neighbors (h=1) as the destination nodes. Thus, for
        each neighbor tuple in the neighbor set where:
             N_status   = SYM
        (there is a symmetric link to the neighbor), and for each
        associated link tuple of the neighbor node such that L_time >=
        current time, a new routing entry is recorded in the routing
        table with:
             R_dest_addr  = L_neighbor_iface_addr, of the
                            associated link tuple;
             R_next_addr  = L_neighbor_iface_addr, of the
                            associated link tuple;
             R_dist       = 1;
             R_iface_addr = L_local_iface_addr of the
                            associated link tuple.
        If in the above, no R_dest_addr is equal to the main address
        of the neighbor, then another new routing entry with MUST be
        added, with:
             R_dest_addr  = main address of the neighbor;
             R_next_addr  = L_neighbor_iface_addr of one of the
                            associated link tuple with L_time >=
             current time;
             R_dist       = 1;
             R_iface_addr = L_local_iface_addr of the
                            associated link tuple.

Clausen & Jacquet Experimental [Page 48] RFC 3626 Optimized Link State Routing October 2003

   3    for each node in N2, i.e., a 2-hop neighbor which is not a
        neighbor node or the node itself, and such that there exist at
        least one entry in the 2-hop neighbor set where
        N_neighbor_main_addr correspond to a neighbor node with
        willingness different of WILL_NEVER, one selects one 2-hop
        tuple and creates one entry in the routing table with:
             R_dest_addr  =  the main address of the 2-hop neighbor;
             R_next_addr  = the R_next_addr of the entry in the
                            routing table with:
                                R_dest_addr == N_neighbor_main_addr
                                               of the 2-hop tuple;
             R_dist       = 2;
             R_iface_addr = the R_iface_addr of the entry in the
                            routing table with:
                                R_dest_addr == N_neighbor_main_addr
                                               of the 2-hop tuple;
   3    The new route entries for the destination nodes h+1 hops away
        are recorded in the routing table.  The following procedure
        MUST be executed for each value of h, starting with h=2 and
        incrementing it by 1 each time.  The execution will stop if no
        new entry is recorded in an iteration.
        3.1  For each topology entry in the topology table, if its
             T_dest_addr does not correspond to R_dest_addr of any
             route entry in the routing table AND its T_last_addr
             corresponds to R_dest_addr of a route entry whose R_dist
             is equal to h, then a new route entry MUST be recorded in
             the routing table (if it does not already exist) where:
                  R_dest_addr  = T_dest_addr;
                  R_next_addr  = R_next_addr of the recorded
                                 route entry where:
                                 R_dest_addr == T_last_addr
                  R_dist       = h+1; and

Clausen & Jacquet Experimental [Page 49] RFC 3626 Optimized Link State Routing October 2003

                  R_iface_addr = R_iface_addr of the recorded
                                 route entry where:
                                    R_dest_addr == T_last_addr.
        3.2  Several topology entries may be used to select a next hop
             R_next_addr for reaching the node R_dest_addr.  When h=1,
             ties should be broken such that nodes with highest
             willingness and MPR selectors are preferred as next hop.
   4    For each entry in the multiple interface association base
        where there exists a routing entry such that:
             R_dest_addr  == I_main_addr  (of the multiple interface
                                          association entry)
        AND there is no routing entry such that:
             R_dest_addr  == I_iface_addr
        then a route entry is created in the routing table with:
             R_dest_addr  =  I_iface_addr (of the multiple interface
                                           association entry)
             R_next_addr  =  R_next_addr  (of the recorded
                                           route entry)
             R_dist       =  R_dist       (of the recorded
                                           route entry)
             R_iface_addr =  R_iface_addr (of the recorded
                                              route entry).

11. Node Configuration

 This section outlines how a node should be configured, in order to
 operate in an OLSR MANET.

11.1. Address Assignment

 The nodes in the MANET network SHOULD be assigned addresses within a
 defined address sequence, i.e., the nodes in the MANET SHOULD be
 addressable through a network address and a netmask.

Clausen & Jacquet Experimental [Page 50] RFC 3626 Optimized Link State Routing October 2003

 Likewise, the nodes in each associated network SHOULD be assigned
 addresses from a defined address sequence, distinct from that being
 used in the MANET.

11.2. Routing Configuration

 Any MANET node with associated networks or hosts SHOULD be configured
 such that it has routes set up to the interfaces with associated
 hosts or network.

11.3. Data Packet Forwarding

 OLSR itself does not perform packet forwarding.  Rather, it maintains
 the routing table in the underlying operating system, which is
 assumed to be forwarding packets as specified in RFC1812.

12. Non OLSR Interfaces

 A node MAY be equipped with multiple interfaces, some of which do not
 participate in the OLSR MANET.  These non OLSR interfaces may be
 point to point connections to other singular hosts or may connect to
 separate networks.
 In order to provide connectivity from the OLSR MANET interface(s) to
 these non OLSR interface(s), a node SHOULD be able to inject external
 route information to the OLSR MANET.
 Injecting routing information from the OLSR MANET to non OLSR
 interfaces is outside the scope of this specification.  It should be
 clear, however, that the routing information for the OLSR MANET can
 be extracted from the topology table (see section 4.4) or directly
 from the routing table of OLSR, and SHOULD be injected onto the non
 OLSR interfaces following whatever mechanism (routing protocol,
 static configuration etc.) is provided on these interfaces.
 An example of such a situation could be where a node is equipped with
 a fixed network (e.g., an Ethernet) connecting to a larger network as
 well as a wireless network interface running OLSR.
 Notice that this is a different case from that of "multiple
 interfaces", where all the interfaces are participating in the MANET
 through running the OLSR protocol.
 In order to provide this capability of injecting external routing
 information into an OLSR MANET, a node with such non-MANET interfaces
 periodically issues a Host and Network Association (HNA) message,
 containing sufficient information for the recipients to construct an
 appropriate routing table.

Clausen & Jacquet Experimental [Page 51] RFC 3626 Optimized Link State Routing October 2003

12.1. HNA Message Format

 The proposed format of an HNA-message is:
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Network Address                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                             Netmask                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Network Address                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                             Netmask                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              ...                              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 This is sent as the data part of the general packet format with the
 "Message Type" set to HNA_MESSAGE, the TTL field set to 255 and Vtime
 set accordingly to the value of HNA_HOLD_TIME, as specified in
 section 18.3.
   Network Address
        The network address of the associated network
   Netmask
        The netmask, corresponding to the network address immediately
        above.

12.2. Host and Network Association Information Base

 Each node maintains information concerning which nodes may act as
 "gateways" to associated hosts and networks by recording "association
 tuples" (A_gateway_addr, A_network_addr, A_netmask, A_time), where
 A_gateway_addr is the address of an OLSR interface of the gateway,
 A_network_addr and A_netmask specify the network address and netmask
 of a network, reachable through this gateway, and A_time specifies
 the time at which this tuple expires and hence *MUST* be removed.
 The set of all association tuples in a node is called the
 "association set".
 It should be noticed, that the HNA-message can be considered as a
 "generalized version" of the TC-message: the originator of both the
 HNA- and TC-messages announce "reachability" to some other host(s).

Clausen & Jacquet Experimental [Page 52] RFC 3626 Optimized Link State Routing October 2003

 In the TC-message, no netmask is required, since all reachability is
 announced on a per-host basis.  In HNA-messages, announcing
 reachability to an address sequence through a network- and netmask
 address is typically preferred over announcing reachability to
 individual host addresses.
 An important difference between TC- and HNA-messages is, that a TC
 message may have a canceling effect on previous information (if the
 ANSN is incremented), whereas information in HNA-messages is removed
 only upon expiration.

12.3. HNA Message Generation

 A node with associated hosts and/or networks SHOULD periodically
 generate a Host and Network Association (HNA) message, containing
 pairs of (network address, netmask) corresponding to the connected
 hosts and networks.  HNA-messages SHOULD be transmitted periodically
 every HNA_INTERVAL.  The Vtime is set accordingly to the value of
 HNA_HOLD_TIME, as specified in section 18.3.
 A node without any associated hosts and/or networks SHOULD NOT
 generate HNA-messages.

12.4. HNA Message Forwarding

 Upon receiving a HNA message, and thus following the rules of section
 3, in this version of the specification, the message MUST be
 forwarded according to section 3.4.

12.5. HNA Message Processing

 In this section, the term "originator address" is used to designate
 the main address on the OLSR MANET of the node which originally
 issued the HNA-message.
 Upon processing a HNA-message, the "validity time" MUST be computed
 from the Vtime field of the message header (see section 3.3.2).  The
 association base SHOULD then be updated as follows:
 1    If the sender interface (NB: not originator) of this message
      is not in the symmetric 1-hop neighborhood of this node, the
      message MUST be discarded.
 2    Otherwise, for each (network address, netmask) pair in the
      message:

Clausen & Jacquet Experimental [Page 53] RFC 3626 Optimized Link State Routing October 2003

      2.1  if an entry in the association set already exists, where:
                A_gateway_addr == originator address
                A_network_addr == network address
                A_netmask      == netmask
           then the holding time for that tuple MUST be set to:
                A_time         =  current time + validity time
      2.2  otherwise, a new tuple MUST be recorded with:
                A_gateway_addr =  originator address
                A_network_addr =  network address
                A_netmask      =  netmask
                A_time         =  current time + validity time

12.6. Routing Table Calculation

 In addition to the routing table computation as described in section
 10, the host and network association set MUST be added as follows:
 For each tuple in the association set,
   1    If there is no entry in the routing table with:
             R_dest_addr     == A_network_addr/A_netmask
        then a new routing entry is created.
   2    If a new routing entry was created at the previous step, or
        else if there existed one with:
             R_dest_addr     == A_network_addr/A_netmask
             R_dist          >  dist to A_gateway_addr of
                                current association set tuple,
        then the routing entry is modified as follows:
             R_dest_addr     =  A_network_addr/A_netmask

Clausen & Jacquet Experimental [Page 54] RFC 3626 Optimized Link State Routing October 2003

             R_next_addr     =  the next hop on the path
                                from the node to A_gateway_addr
             R_dist          =  dist to A_gateway_addr
             R_next_addr and R_iface_addr MUST be set to the same
             values as the tuple from the routing set with R_dest_addr
             == A_gateway_addr.

12.7. Interoperability Considerations

 Nodes, which do not implement support for non OLSR interfaces, can
 coexist in a network with nodes which do implement support for non
 OLSR interfaces: the generic packet format and message forwarding
 (section 3) ensures that HNA messages are correctly forwarded by all
 nodes.  Nodes which implement support for non OLSR interfaces may
 thus transmit and process HNA messages according to this section.
 Nodes, which do not implement support for non OLSR interfaces can not
 take advantage of the functionality specified in this section,
 however they will forward HNA messages correctly, as specified in
 section 3.

13. Link Layer Notification

 OLSR is designed not to impose or expect any specific information
 from the link layer.  However, if information from the link-layer
 describing link breakage is available, a node MAY use this as
 described in this section.
 If link layer information describing connectivity to neighboring
 nodes is available (i.e., loss of connectivity such as through
 absence of a link layer acknowledgment), this information is used in
 addition to the information from the HELLO-messages to maintain the
 neighbor information base and the MPR selector set.
 Thus, upon receiving a link-layer notification that the link between
 a node and a neighbor interface is broken, the following actions are
 taken with respect to link sensing:
 Each link tuple in the local link set SHOULD, in addition to what is
 described in section 4.2, include a L_LOST_LINK_time field.
 L_LOST_LINK_time is a timer for declaring a link as lost when an
 established link becomes pending.  (Notice, that this is a subset of
 what is recommended in section 14, thus link hysteresis and link
 layer notifications can coexist).

Clausen & Jacquet Experimental [Page 55] RFC 3626 Optimized Link State Routing October 2003

 HELLO message generation should consider those new fields as follows:
   1    if L_LOST_LINK_time is not expired, the link is advertised
        with a link type of LOST_LINK.  In addition, it is not
        considered as a symmetric link in the updates of the
        associated neighbor tuple (see section 8.1).
   2    if the link to a neighboring symmetric or asymmetric interface
        is broken, the corresponding link tuple is modified:
        L_LOST_LINK_time and L_time are set to current time +
        NEIGHB_HOLD_TIME.
   3    this is considered as a link loss and the appropriate
        processing described in section 8.5 should be
        performed.

13.1. Interoperability Considerations

 Link layer notifications provide, for a node, an additional criterion
 by which a node may determine if a link to a neighbor node is lost.
 Once a link is detected as lost, it is advertised, in accordance with
 the provisions described in the previous sections of this
 specification.

14. Link Hysteresis

 Established links should be as reliable as possible to avoid data
 packet loss.  This implies that link sensing should be robust against
 bursty loss or transient connectivity between nodes.  Hence, to
 enhance the robustness of the link sensing mechanism, the following
 implementation recommendations SHOULD be considered.

14.1. Local Link Set

 Each link tuple in the local link set SHOULD, in addition to what is
 described in section 4.2, include a L_link_pending field, a
 L_link_quality field, and a L_LOST_LINK_time field.  L_link_pending
 is a boolean value specifying if the link is considered pending
 (i.e., the link is not considered established).  L_link_quality is a
 dimensionless number between 0 and 1 describing the quality of the
 link.  L_LOST_LINK_time is a timer for declaring a link as lost when
 an established link becomes pending.

Clausen & Jacquet Experimental [Page 56] RFC 3626 Optimized Link State Routing October 2003

14.2. Hello Message Generation

 HELLO message generation should consider those new fields as follows:
   1    if L_LOST_LINK_time is not expired, the link is advertised
        with a link type of LOST_LINK.
   2    otherwise, if L_LOST_LINK_time is expired and L_link_pending
        is set to "true", the link SHOULD NOT be advertised at all;
   3    otherwise, if L_LOST_LINK_time is expired and L_link_pending
        is set to "false", the link is advertised as described
        previously in section 6.
 A node considers that it has a symmetric link for each link tuple
 where:
   1    L_LOST_LINK_time is expired, AND
   2    L_link_pending is "false", AND
   3    L_SYM_time is not expired.
 This definition for "symmetric link" SHOULD be used in updating the
 associated neighbor tuple (see section 8.1) for computing the
 N_status of a neighbor node.  This definition SHOULD thereby also be
 used as basis for the symmetric neighborhood when computing the MPR
 set, as well as for "the symmetric neighbors" in the first steps of
 the routing table calculation.
 Apart from the above, what has been described previously does not
 interfere with the advanced link sensing fields in the link tuples.
 The L_link_quality, L_link_pending and L_LOST_LINK_time fields are
 exclusively updated according to the present section.  This section
 does not modify the function of any other fields in the link tuples.

14.3. Hysteresis Strategy

 The link between a node and some of its neighbor interfaces might be
 "bad", i.e., from time to time let HELLOs pass through only to fade
 out immediately after.  In this case, the neighbor information base
 would contain a bad link for at least "validity time".  The following
 hysteresis strategy SHOULD be adopted to counter this situation.
 For each neighbor interface NI heard by interface I, the
 L_link_quality field of the corresponding Link Tuple determines the
 establishment of the link.  The value of L_link_quality is compared
 to two thresholds HYST_THRESHOLD_HIGH, HYST_THRESHOLD_LOW, fixed

Clausen & Jacquet Experimental [Page 57] RFC 3626 Optimized Link State Routing October 2003

 between 0 and 1 and such that HYST_THRESHOLD_HIGH >=
 HYST_THRESHOLD_LOW.
 The L_link_pending field is set according to the following:
   1    if L_link_quality > HYST_THRESHOLD_HIGH:
             L_link_pending   = false
             L_LOST_LINK_time = current time - 1 (expired)
   2    otherwise, if L_link_quality < HYST_THRESHOLD_LOW:
             L_link_pending   = true
             L_LOST_LINK_time = min (L_time, current time +
             NEIGHB_HOLD_TIME)
             (the link is then considered as lost according to section
             8.5 and this may produce a neighbor loss).
   3    otherwise, if HYST_THRESHOLD_LOW <= L_link_quality
                                         <= HYST_THRESHOLD_HIGH:
             L_link_pending and L_LOST_LINK_time remain unchanged.
 The condition for considering a link established is thus stricter
 than the condition for dropping a link.  Notice thus, that a link can
 be dropped based on either timer expiration (as described in section
 7) or on L_link_quality dropping below HYST_THRESHOLD_LOW.
 Also notice, that even if a link is not considered as established by
 the link hysteresis, the link tuples are still updated for each
 received HELLO message (as described in section 7).  Specifically,
 this implies that, regardless of whether or not the link hysteresis
 considers a link as "established", tuples in the link set do not
 expire except as determined by the L_time field of the link tuples.
 As a basic implementation requirement, an estimation of the link
 quality must be maintained and stored in the L_link_quality field.
 If some measure of the signal/noise level on a received message is
 available (e.g., as a link layer notification), then it can be used
 as estimation after normalization.
 If no signal/noise information or other link quality information is
 available from the link layer, an algorithm such as the following can
 be utilized (it is an exponentially smoothed moving average of the
 transmission success rate).  The algorithm is parameterized by a

Clausen & Jacquet Experimental [Page 58] RFC 3626 Optimized Link State Routing October 2003

 scaling parameter HYST_SCALING which is a number fixed between 0 and
 1.  For each neighbor interface NI heard by interface I, the first
 time NI is heard by I, L_link_quality is set to HYST_SCALING
 (L_link_pending is set to true and L_LOST_LINK_time to current time -
 1).
 A tuple is updated according to two rules.  Every time an OLSR packet
 emitted by NI is received by I, the stability rule is applied:
        L_link_quality = (1-HYST_SCALING)*L_link_quality
                         + HYST_SCALING.
   When an OLSR packet emitted by NI is lost by I, the instability
   rule is applied:
        L_link_quality = (1-HYST_SCALING)*L_link_quality.
 The loss of OLSR packet is detected by tracking the missing Packet
 Sequence Numbers on a per interface basis and by "long period of
 silence" from a node.  A "long period of silence may be detected
 thus: if no OLSR packet has been received on interface I from
 interface NI during HELLO emission interval of interface NI (computed
 from the Htime field in the last HELLO message received from NI), a
 loss of an OLSR packet is detected.

14.4. Interoperability Considerations

 Link hysteresis determines, for a node, the criteria at which a link
 to a neighbor node is accepted or rejected.  Nodes in a network may
 have different criteria, according to the nature of the media over
 which they are communicating.  Once a link is accepted, it is
 advertised, in accordance with the provisions described in the
 previous sections of this specification.

15. Redundant Topology Information

 In order to provide redundancy to topology information base, the
 advertised link set of a node MAY contain links to neighbor nodes
 which are not in MPR selector set of the node.  The advertised link
 set MAY contain links to the whole neighbor set of the node.  The
 minimal set of links that any node MUST advertise in its TC messages
 is the links to its MPR selectors.  The advertised link set can be
 built according to the following rule based on a local parameter
 called TC_REDUNDANCY parameter.

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15.1. TC_REDUNDANCY Parameter

 The parameter TC_REDUNDANCY specifies, for the local node, the amount
 of information that MAY be included in the TC messages.  The
 parameter SHOULD be interpreted as follows:
  1. if the TC_REDUNDANCY parameter of the node is 0, then the

advertised link set of the node is limited to the MPR

        selector set (as described in section 8.3),
  1. if the TC_REDUNDANCY parameter of the node is 1, then the

advertised link set of the node is the union of its MPR set

        and its MPR selector set,
  1. if the TC_REDUNDANCY parameter of the node is 2, then the

advertised link set of the node is the full neighbor link set.

 A node with willingness equal to WILL_NEVER SHOULD have TC_REDUNDANCY
 also equal to zero.

15.2. Interoperability Considerations

 A TC message is sent by a node in the network to declare a set of
 links, called advertised link set, which MUST include at least the
 links to all nodes of its MPR Selector set, i.e., the neighbors which
 have selected the sender node as a MPR.  This is sufficient
 information to ensure that routes can be computed in accordance with
 section 10.
 The provisions in this section specifies how additional information
 may be declared, as specified through a TC_REDUNDANCY parameter.
 TC_REDUNDANCY = 0 implies that the information declared corresponds
 exactly to the MPR Selector set, identical to section 9.  Other
 values of TC_REDUNDANCY specifies additional information to be
 declared, i.e., the contents of the MPR Selector set is always
 declared.  Thus, nodes with different values of TC_REDUNDANCY may
 coexist in a network: control messages are carried by all nodes in
 accordance with section 3, and all nodes will receive at least the
 link-state information required to construct routes as described in
 section 10.

16. MPR Redundancy

 MPR redundancy specifies the ability for a node to select redundant
 MPRs.  Section 4.5 specifies that a node should select its MPR set to
 be as small as possible, in order to reduce protocol overhead.  The
 criteria for selecting MPRs is, that all strict 2-hop nodes must be
 reachable through, at least, one MPR node.  Redundancy of the MPR set

Clausen & Jacquet Experimental [Page 60] RFC 3626 Optimized Link State Routing October 2003

 affects the overhead through affecting the amount of links being
 advertised, the amount of nodes advertising links and the efficiency
 of the MPR flooding mechanism.  On the other hand, redundancy in the
 MPR set ensures that reachability for a node is advertised by more
 nodes, thus additional links are diffused to the network.
 While, in general, a minimal MPR set provides the least overhead,
 there are situations in which overhead can be traded off for other
 benefits.  For example, a node may decide to increase its MPR
 coverage if it observes many changes in its neighbor information base
 caused by mobility, while otherwise keeping a low MPR coverage.

16.1. MPR_COVERAGE Parameter

 The MPR coverage is defined by a single local parameter,
 MPR_COVERAGE, specifying by how many MPR nodes any strict 2-hop node
 should be covered.  MPR_COVERAGE=1 specifies that the overhead of the
 protocol is kept at a minimum and causes the MPR selection to operate
 as described in section 8.3.1.  MPR_COVERAGE=m ensures that, if
 possible, a node selects its MPR set such that all strict 2-hop nodes
 for an interface are reachable through at least m MPR nodes on that
 interface.  MPR_COVERAGE can assume any integer value > 0.  The
 heuristic MUST be applied per interface, I.  The MPR set for a node
 is the union of the MPR sets found for each interface.
 Notice that MPR_COVERAGE can be tuned locally without affecting the
 consistency of the protocol.  For example, nodes in a network may
 operate with different values of MPR_COVERAGE.

16.2. MPR Computation

 Using MPR coverage, the MPR selection heuristics is extended from
 that described in the section 8.3.1 by one definition:
   Poorly covered node:
        A poorly covered node is a node in N2 which is covered by less
        than MPR_COVERAGE nodes in N.
 The proposed heuristic for selecting MPRs is then as follows:
   1    Start with an MPR set made of all members of N with
        willingness equal to WILL_ALWAYS
   2    Calculate D(y), where y is a member of N, for all nodes in N.

Clausen & Jacquet Experimental [Page 61] RFC 3626 Optimized Link State Routing October 2003

   3    Select as MPRs those nodes in N which cover the poorly covered
        nodes in N2.  The nodes are then removed from N2 for the rest
        of the computation.
   4    While there exist nodes in N2 which are not covered by at
        least MPR_COVERAGE nodes in the MPR set:
        4.1  For each node in N, calculate the reachability, i.e.,
             the number of nodes in N2 which are not yet covered
             by at least MPR_COVERAGE nodes in the MPR set, and
             which are reachable through this 1-hop neighbor;
        4.2  Select as a MPR the node with highest willingness among
             the nodes in N with non-zero reachability.  In case of
             multiple choice select the node which provides
             reachability to the maximum number of nodes in N2.  In
             case of multiple nodes providing the same amount of
             reachability, select the node as MPR whose D(y) is
             greater.  Remove the nodes from N2 which are now covered
             by MPR_COVERAGE nodes in the MPR set.
   5    A node's MPR set is generated from the union of the MPR sets
        for each interface.  As an optimization, process each node, y,
        in the MPR set in increasing order of N_willingness.  If all
        nodes in N2 are still covered by at least MPR_COVERAGE nodes
        in the MPR set excluding node y, and if N_willingness of node
        y is smaller than WILL_ALWAYS, then node y MAY be removed from
        the MPR set.
 When the MPR set has been computed, all the corresponding main
 addresses are stored in the MPR Set.

16.3. Interoperability Considerations

 The MPR set of a node MUST, according to section 8.3, be calculated
 by a node in such a way that it, through the neighbors in the MPR-
 set, can reach all symmetric strict 2-hop neighbors.  This is
 achieved by the heuristics in this section, for all values of
 MPR_COVERAGE > 0.  MPR_COVERAGE is a local parameter for each node.
 Setting this parameter affects only the amount of redundancy in part
 of the network.
 Notice that for MPR_COVERAGE=1, the heuristics in this section is
 identical to the heuristics specified in the section 8.3.1.

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 Nodes with different values of MPR_COVERAGE may coexist in a network:
 control messages are carried by all nodes in accordance with section
 3, and all nodes will receive at least the link-state information
 required to construct routes as described in sections 9 and 10.

17. IPv6 Considerations

 All the operations and parameters described in this document used by
 OLSR for IP version 4 are the same as those used by OLSR for IP
 version 6.  To operate with IP version 6, the only required change is
 to replace the IPv4 addresses with IPv6 address.  The minimum packet
 and message sizes (under which there is rejection) should be adjusted
 accordingly, considering the greater size of IPv6 addresses.

18. Proposed Values for Constants

 This section list the values for the constants used in the
 description of the protocol.

18.1. Setting emission intervals and holding times

 The proposed constant for C is the following:
        C = 1/16 seconds (equal to 0.0625 seconds)
 C is a scaling factor for the "validity time" calculation ("Vtime"
 and "Htime" fields in message headers, see section 18.3).  The
 "validity time" advertisement is designed such that nodes in a
 network may have different and individually tuneable emission
 intervals, while still interoperate fully.  For protocol functioning
 and interoperability to work:
  1. the advertised holding time MUST always be greater than the

refresh interval of the advertised information. Moreover, it

        is recommended that the relation between the interval (from
        section 18.2), and the hold time is kept as specified
        in section 18.3, to allow for reasonable packet loss.
  1. the constant C SHOULD be set to the suggested value. In order

to achieve interoperability, C MUST be the same on all nodes.

  1. the emission intervals (section 18.2), along with the

advertised holding times (subject to the above constraints)

        MAY be selected on a per node basis.
 Note that the timer resolution of a given implementation might not be
 sufficient to wake up the system on precise refresh times or on
 precise expire times: the implementation SHOULD round up the

Clausen & Jacquet Experimental [Page 63] RFC 3626 Optimized Link State Routing October 2003

 'validity time' ("Vtime" and "Htime" of packets) to compensate for
 coarser timer resolution, at least in the case where "validity time"
 could be shorter than the sum of emission interval and maximum
 expected timer error.

18.2. Emission Intervals

        HELLO_INTERVAL        = 2 seconds
        REFRESH_INTERVAL      = 2 seconds
        TC_INTERVAL           = 5 seconds
        MID_INTERVAL          = TC_INTERVAL
        HNA_INTERVAL          = TC_INTERVAL

18.3. Holding Time

        NEIGHB_HOLD_TIME      = 3 x REFRESH_INTERVAL
        TOP_HOLD_TIME         = 3 x TC_INTERVAL
        DUP_HOLD_TIME         = 30 seconds
        MID_HOLD_TIME         = 3 x MID_INTERVAL
        HNA_HOLD_TIME         = 3 x HNA_INTERVAL
 The Vtime in the message header (see section 3.3.2), and the Htime in
 the HELLO message (see section 6.1) are the fields which hold
 information about the above values in mantissa and exponent format
 (rounded up).  In other words:
   value = C*(1+a/16)*2^b [in seconds]
 where a is the integer represented by the four highest bits of the
 field and b the integer represented by the four lowest bits of the
 field.
 Notice, that for the previous proposed value of C, (1/16 seconds),
 the values, in seconds, expressed by the formula above can be stored,
 without loss of precision, in binary fixed point or floating point
 numbers with at least 8 bits of fractional part.  This corresponds
 with NTP time-stamps and single precision IEEE Standard 754 floating
 point numbers.

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 Given one of the above holding times, a way of computing the
 mantissa/exponent representation of a number T (of seconds) is the
 following:
  1. find the largest integer 'b' such that: T/C >= 2^b
  1. compute the expression 16*(T/(C*(2^b))-1), which may not be a

integer, and round it up. This results in the value for 'a'

  1. if 'a' is equal to 16: increment 'b' by one, and set 'a' to 0
  1. now, 'a' and 'b' should be integers between 0 and 15, and the

field will be a byte holding the value a*16+b

 For instance, for values of 2 seconds, 6 seconds, 15 seconds, and 30
 seconds respectively, a and b would be: (a=0,b=5), (a=8,b=6),
 (a=14,b=7) and (a=14,b=8) respectively.

18.4. Message Types

        HELLO_MESSAGE         = 1
        TC_MESSAGE            = 2
        MID_MESSAGE           = 3
        HNA_MESSAGE           = 4

18.5. Link Types

        UNSPEC_LINK           = 0
        ASYM_LINK             = 1
        SYM_LINK              = 2
        LOST_LINK             = 3

18.6. Neighbor Types

        NOT_NEIGH             = 0
        SYM_NEIGH             = 1
        MPR_NEIGH             = 2

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18.7. Link Hysteresis

        HYST_THRESHOLD_HIGH   = 0.8
        HYST_THRESHOLD_LOW    = 0.3
        HYST_SCALING          = 0.5

18.8. Willingness

        WILL_NEVER            = 0
        WILL_LOW              = 1
        WILL_DEFAULT          = 3
        WILL_HIGH             = 6
        WILL_ALWAYS           = 7
 The willingness of a node may be set to any integer value from 0 to
 7, and specifies how willing a node is to be forwarding traffic on
 behalf of other nodes.  Nodes will, by default, have a willingness
 WILL_DEFAULT.  WILL_NEVER indicates a node which does not wish to
 carry traffic for other nodes, for example due to resource
 constraints (like being low on battery).  WILL_ALWAYS indicates that
 a node always should be selected to carry traffic on behalf of other
 nodes, for example due to resource abundance (like permanent power
 supply, high capacity interfaces to other nodes).
 A node may dynamically change its willingness as its conditions
 change.
 One possible application would, for example, be for a node, connected
 to a permanent power supply and with fully charged batteries, to
 advertise a willingness of WILL_ALWAYS.  Upon being disconnected from
 the permanent power supply (e.g., a PDA being taken out of its
 charging cradle), a willingness of WILL_DEFAULT is advertised.  As
 battery capacity is drained, the willingness would be further
 reduced.  First to the intermediate value between WILL_DEFAULT and
 WILL_LOW, then to WILL_LOW and finally to WILL_NEVER, when the
 battery capacity of the node does no longer support carrying foreign
 traffic.

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18.9. Misc. Constants

        TC_REDUNDANCY         = 0
        MPR COVERAGE          = 1
        MAXJITTER             = HELLO_INTERVAL / 4

19. Sequence Numbers

 Sequence numbers are used in OLSR with the purpose of discarding
 "old" information, i.e., messages received out of order.  However
 with a limited number of bits for representing sequence numbers,
 wrap-around (that the sequence number is incremented from the maximum
 possible value to zero) will occur.  To prevent this from interfering
 with the operation of the protocol, the following MUST be observed.
 The term MAXVALUE designates in the following the largest possible
 value for a sequence number.
 The sequence number S1 is said to be "greater than" the sequence
 number S2 if:
        S1 > S2 AND S1 - S2 <= MAXVALUE/2 OR
        S2 > S1 AND S2 - S1 > MAXVALUE/2
 Thus when comparing two messages, it is possible - even in the
 presence of wrap-around - to determine which message contains the
 most recent information.

20. Security Considerations

 Currently, OLSR does not specify any special security measures.  As a
 proactive routing protocol, OLSR makes a target for various attacks.
 The various possible vulnerabilities are discussed in this section.

20.1. Confidentiality

 Being a proactive protocol, OLSR periodically diffuses topological
 information.  Hence, if used in an unprotected wireless network, the
 network topology is revealed to anyone who listens to OLSR control
 messages.

Clausen & Jacquet Experimental [Page 67] RFC 3626 Optimized Link State Routing October 2003

 In situations where the confidentiality of the network topology is of
 importance, regular cryptographic techniques such as exchange of OLSR
 control traffic messages encrypted by PGP [9] or encrypted by some
 shared secret key can be applied to ensure that control traffic can
 be read and interpreted by only those authorized to do so.

20.2. Integrity

 In OLSR, each node is injecting topological information into the
 network through transmitting HELLO messages and, for some nodes, TC
 messages.  If some nodes for some reason, malicious or malfunction,
 inject invalid control traffic, network integrity may be compromised.
 Therefore, message authentication is recommended.
 Different such situations may occur, for instance:
   1    a node generates TC (or HNA) messages, advertising links to
        non-neighbor nodes:
   2    a node generates TC (or HNA) messages, pretending to be
        another node,
   3    a node generates HELLO messages, advertising non-neighbor
        nodes,
   4    a node generates HELLO messages, pretending to be another
        node.
   5    a node forwards altered control messages,
   6    a node does not broadcast control messages,
   7    a node does not select multipoint relays correctly.
   8    a node forwards broadcast control messages unaltered, but does
        not forward unicast data traffic;
   9    a node "replays" previously recorded control traffic from
        another node.
 Authentication of the originator node for control messages (for
 situation 2, 4 and 5) and on the individual links announced in the
 control messages (for situation 1 and 3) may be used as a
 countermeasure.  However to prevent nodes from repeating old (and
 correctly authenticated) information (situation 9) temporal
 information is required, allowing a node to positively identify such
 delayed messages.

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 In general, digital signatures and other required security
 information may be transmitted as a separate OLSR message type,
 thereby allowing that "secured" and "unsecured" nodes can coexist in
 the same network, if desired.
 Specifically, the authenticity of entire OLSR control messages can be
 established through employing IPsec authentication headers, whereas
 authenticity of individual links (situation 1 and 3) require
 additional security information to be distributed.
 An important consideration is, that all control messages in OLSR are
 transmitted either to all nodes in the neighborhood (HELLO messages)
 or broadcast to all nodes in the network (e.g., TC messages).
 For example, a control message in OLSR is always a point-to-
 multipoint transmission.  It is therefore important that the
 authentication mechanism employed permits that any receiving node can
 validate the authenticity of a message.  As an analogy, given a block
 of text, signed by a PGP private key, then anyone with the
 corresponding public key can verify the authenticity of the text.

20.3. Interaction with External Routing Domains

 OLSR does, through the HNA messages specified in section 12, provide
 a basic mechanism for injecting external routing information to the
 OLSR domain.  Section 12 also specifies that routing information can
 be extracted from the topology table or the routing table of OLSR
 and, potentially, injected into an external domain if the routing
 protocol governing that domain permits.
 Other than as described in the section 20.2, when operating nodes,
 connecting OLSR to an external routing domain, care MUST be taken not
 to allow potentially insecure and un-trustworthy information to be
 injected from the OLSR domain to external routing domains.  Care MUST
 be taken to validate the correctness of information prior to it being
 injected as to avoid polluting routing tables with invalid
 information.
 A recommended way of extending connectivity from an existing routing
 domain to an OLSR routed MANET is to assign an IP prefix (under the
 authority of the nodes/gateways connecting the MANET with the exiting
 routing domain) exclusively to the OLSR MANET area, and to configure
 the gateways statically to advertise routes to that IP sequence to
 nodes in the existing routing domain.

Clausen & Jacquet Experimental [Page 69] RFC 3626 Optimized Link State Routing October 2003

20.4. Node Identity

 OLSR does not make any assumption about node addresses, other than
 that each node is assumed to have a unique IP address.

21. Flow and congestion control

 Due to its proactive nature, the OLSR protocol has a natural control
 over the flow of its control traffic.  Nodes transmits control
 message at predetermined rates fixed by predefined refresh intervals.
 Furthermore the MPR optimization greatly saves on control overhead,
 and this is done on two sides.  First, the packets that advertise the
 topology are much shorter since only MPR selectors may be advertised.
 Second, the cost of flooding this information is greatly reduced
 since only MPR nodes forward the broadcast packets.  In dense
 networks, the reduction of control traffic can be of several orders
 of magnitude compared to routing protocols using classical flooding
 (such as OSPF) [10].  This feature naturally provides more bandwidth
 for useful data traffic and pushes further the frontier of
 congestion.  Since the control traffic is continuous and periodic, it
 keeps more stable the quality of the links used in routing, where
 reactive protocols, with bursty floodings for route discoveries and
 repairs, may damage the link qualities for short times by causing
 numerous collisions on those links, possibly provoking route repair
 cascades.  However, in certain OLSR options, some control messages
 may be intentionally sent in advance of their deadline(TC or Hello
 messages) in order to increase the reactiveness of the protocol
 against topology changes.  This may cause a small, temporary and
 local increase of control traffic.

22. IANA Considerations

 OLSR defines a "Message Type" field for control messages.  A new
 registry has been created for the values for this Message Type field,
 and the following values assigned:
     Message Type             Value
    --------------------      -----
     HELLO_MESSAGE              1
     TC_MESSAGE                 2
     MID_MESSAGE                3
     HNA_MESSAGE                4
 Future values in the range 5-127 of the Message Type can be allocated
 using standards action [7].
 Additionally, values in the range 128-255 are reserved for
 private/local use.

Clausen & Jacquet Experimental [Page 70] RFC 3626 Optimized Link State Routing October 2003

23. Acknowledgments

 The authors would like to thank Joseph Macker
 <macker@itd.nrl.navy.mil> and his team, including Justin Dean
 <jdean@itd.nrl.navy.mil>, for their valuable suggestions on the
 advanced neighbor sensing mechanism and other various aspects of the
 protocol, including careful review of the protocol specification.
 The authors would also like to thank Christopher Dearlove
 <chris.dearlove@baesystems.com> for valuable input on the MPR
 selection heuristics and for careful reviews of the protocol
 specification.

24. Contributors

 During the development of this specification, the following list of
 people contributed.  The contributors are listed alphabetically.
 Cedric Adjih
 Project HIPERCOM
 INRIA Rocquencourt, BP 105
 78153 Le Chesnay Cedex, France
 Phone: +33 1 3963 5215
 EMail: Cedric.Adjih@inria.fr
 Thomas Heide Clausen
 Project HIPERCOM
 INRIA Rocquencourt, BP 105
 78153 Le Chesnay Cedex, France
 Phone: +33 1 3963 5133
 EMail: T.Clausen@computer.org
 Philippe Jacquet
 Project HIPERCOM
 INRIA Rocquencourt, BP 105
 78153 Le Chesnay Cedex, France
 Phone: +33 1 3963 5263
 EMail: Philippe.Jacquet@inria.fr

Clausen & Jacquet Experimental [Page 71] RFC 3626 Optimized Link State Routing October 2003

 Anis Laouiti
 Project HIPERCOM
 INRIA Rocquencourt, BP 105
 78153 Le Chesnay Cedex, France
 Phone: +33 1 3963 5088
 EMail: Anis.Laouiti@inria.fr
 Pascale Minet
 Project HIPERCOM
 INRIA Rocquencourt, BP 105
 78153 Le Chesnay Cedex, France
 Phone: +33 1 3963 5233
 EMail: Pascale.Minet@inria.fr
 Paul Muhlethaler
 Project HIPERCOM
 INRIA Rocquencourt, BP 105
 78153 Le Chesnay Cedex, France
 Phone: +33 1 3963 5278
 EMail: Paul.Muhlethaler@inria.fr
 Amir Qayyum
 Center for Advanced Research in Engineering Pvt. Ltd.
 19 Ataturk Avenue
 Islamabad, Pakistan
 Phone: +92-51-2874115
 EMail: amir@carepvtltd.com
 Laurent Viennot
 Project HIPERCOM
 INRIA Rocquencourt, BP 105
 78153 Le Chesnay Cedex, France
 Phone: +33 1 3963 5225
 EMail: Laurent.Viennot@inria.fr

Clausen & Jacquet Experimental [Page 72] RFC 3626 Optimized Link State Routing October 2003

25. References

25.1. Normative References

 [5]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.
 [7]   T.  Clausen, P.  Jacquet, A.  Laouiti, P.  Muhlethaler, A.
       Qayyum and L.  Viennot.  Optimized Link State Routing Protocol.
       IEEE INMIC Pakistan 2001.

25.2. Informative References

 [1]   P. Jacquet, P. Minet, P. Muhlethaler, N. Rivierre.  Increasing
       reliability in cable free radio LANs: Low level forwarding in
       HIPERLAN.  Wireless Personal Communications, 1996.
 [2]   A.  Qayyum, L.  Viennot, A.  Laouiti.  Multipoint relaying: An
       efficient technique for flooding in mobile wireless networks.
       35th Annual Hawaii International Conference on System Sciences
       (HICSS'2001).
 [3]   ETSI STC-RES10 Committee.  Radio equipment and systems:
       HIPERLAN type 1, functional specifications ETS 300-652, ETSI,
       June 1996.
 [4]   P. Jacquet and L. Viennot, Overhead in Mobile Ad-hoc Network
       Protocols, INRIA research report RR-3965, 2000.
 [6]   T. Clausen, G. Hansen, L. Christensen and G. Behrmann.  The
       Optimized Link State Routing Protocol, Evaluation through
       Experiments and Simulation.  IEEE Symposium on "Wireless
       Personal Mobile Communications", September 2001.
 [8]   Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
       Considerations Section in RFCs",  BCP 26, RFC 2434, October
       1998.
 [9]   Atkins, D., Stallings, W. and P. Zimmermann, "PGP Message
       Exchange Formats", RFC 1991, August 1996.
 [10]  P. Jacquet, A. Laouiti, P. Minet, L. Viennot.  Performance
       analysis of OLSR multipoint relay flooding in two ad hoc
       wireless network models, INRIA research report RR-4260, 2001.

Clausen & Jacquet Experimental [Page 73] RFC 3626 Optimized Link State Routing October 2003

26. Authors' Addresses

 Thomas Heide Clausen
 Project HIPERCOM
 INRIA Rocquencourt, BP 105
 78153 Le Chesnay Cedex, France
 Phone: +33 1 3963 5133
 EMail: T.Clausen@computer.org
 Philippe Jacquet,
 Project HIPERCOM,
 INRIA Rocquencourt, BP 105
 78153 Le Chesnay Cedex, France
 Phone: +33 1 3963 5263,
 EMail: Philippe.Jacquet@inria.fr

Clausen & Jacquet Experimental [Page 74] RFC 3626 Optimized Link State Routing October 2003

27. Full Copyright Statement

 Copyright (C) The Internet Society (2003).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assignees.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Clausen & Jacquet Experimental [Page 75]

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