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rfc:rfc4883

Network Working Group G. Feher Request for Comments: 4883 K. Nemeth Category: Informational A. Korn

                                                                  BUTE
                                                           I. Cselenyi
                                                           TeliaSonera
                                                             July 2007
 Benchmarking Terminology for Resource Reservation Capable Routers

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The IETF Trust (2007).

Abstract

 The primary purpose of this document is to define terminology
 specific to the benchmarking of resource reservation signaling of
 Integrated Services (IntServ) IP routers.  These terms can be used in
 additional documents that define benchmarking methodologies for
 routers that support resource reservation or reporting formats for
 the benchmarking measurements.

Feher, et al. Informational [Page 1] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

Table of Contents

 1. Introduction ....................................................2
 2. Existing Definitions ............................................3
 3. Definition of Terms .............................................4
    3.1. Traffic Flow Types .........................................4
         3.1.1. Data Flow ...........................................4
         3.1.2. Distinguished Data Flow .............................4
         3.1.3. Best-Effort Data Flow ...............................5
    3.2. Resource Reservation Protocol Basics .......................5
         3.2.1. QoS Session .........................................5
         3.2.2. Resource Reservation Protocol .......................6
         3.2.3. Resource Reservation Capable Router .................7
         3.2.4. Reservation State ...................................7
         3.2.5. Resource Reservation Protocol Orientation ...........8
    3.3. Router Load Factors ........................................9
         3.3.1. Best-Effort Traffic Load Factor .....................9
         3.3.2. Distinguished Traffic Load Factor ..................10
         3.3.3. Session Load Factor ................................11
         3.3.4. Signaling Intensity Load Factor ....................11
         3.3.5. Signaling Burst Load Factor ........................12
    3.4. Performance Metrics .......................................13
         3.4.1. Signaling Message Handling Time ....................13
         3.4.2. Distinguished Traffic Delay ........................14
         3.4.3. Best-effort Traffic Delay ..........................15
         3.4.4. Signaling Message Deficit ..........................15
         3.4.5. Session Maintenance Capacity .......................16
    3.5. Router Load Conditions and Scalability Limit ..............17
         3.5.1. Loss-Free Condition ................................17
         3.5.2. Lossy Condition ....................................18
         3.5.3. QoS Compliant Condition ............................19
         3.5.4. Not QoS Compliant Condition ........................20
         3.5.5. Scalability Limit ..................................20
 4. Security Considerations ........................................21
 5. Acknowledgements ...............................................21
 6. References .....................................................21
    6.1. Normative References ......................................21
    6.2. Informative References ....................................21

1. Introduction

 Signaling-based resource reservation using the IntServ paradigm [4]
 is an important part of the different Quality of Service (QoS)
 provisioning approaches.  Therefore, network operators who are
 planning to deploy signaling-based resource reservation may want to
 examine the scalability limitations of reservation capable routers
 and the impact of signaling on their data forwarding performance.

Feher, et al. Informational [Page 2] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

 An objective way of quantifying the scalability constraints of QoS
 signaling is to perform measurements on routers that are capable of
 IntServ-based resource reservation.  This document defines
 terminology for a specific set of tests that vendors or network
 operators can carry out to measure and report the signaling
 performance characteristics of router devices that support resource
 reservation protocols.  The results of these tests provide comparable
 data for different products, and thus support the decision-making
 process before purchase.  Moreover, these measurements provide input
 characteristics for the dimensioning of a network in which resources
 are provisioned dynamically by signaling.  Finally, the tests are
 applicable for characterizing the impact of the resource reservation
 signaling on the forwarding performance of the routers.
 This benchmarking terminology document is based on the knowledge
 gained by examination of (and experimentation with) different
 resource reservation protocols: the IETF standard Resource
 ReSerVation Protocol (RSVP) [5], Next Steps in Signaling (NSIS)
 [6][7][8][9], and several experimental ones, such as YESSIR (Yet
 Another Sender Session Internet Reservation) [10], ST2+ [11], Session
 Description Protocol (SDP) [12], Boomerang [13], and Ticket [14].
 Some of these protocols were also analyzed by the IETF NSIS working
 group [15].  Although at the moment the authors are only aware of
 resource reservation capable router products that interpret RSVP,
 this document defines terms that are valid in general and not
 restricted to any of the protocols listed above.
 In order to avoid any confusion, we would like to emphasize that this
 terminology considers only signaling protocols that provide IntServ
 resource reservation; for example, techniques in the DiffServ toolbox
 are predominantly beyond our scope.

2. Existing Definitions

 RFC 1242 "Benchmarking Terminology for Network Interconnection
 Devices" [1] and RFC 2285 "Benchmarking Terminology for LAN Switching
 Devices" [3] contain discussions and definitions for a number of
 terms relevant to the benchmarking of signaling performance of
 reservation-capable routers and should be consulted before attempting
 to make use of this document.
 Additionally, this document defines terminology in a way that is
 consistent with the terms used by the Next Steps in Signaling working
 group laid out in [6][7][8].
 For the sake of clarity and continuity, this document adopts the
 template for definitions set out in Section 2 of RFC 1242.

Feher, et al. Informational [Page 3] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

 Definitions are indexed and grouped together into different sections
 for ease of reference.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [2].

3. Definition of Terms

3.1. Traffic Flow Types

 This group of definitions describes traffic flow types forwarded by
 resource reservation capable routers.

3.1.1. Data Flow

 Definition:
    A data flow is a stream of data packets from one sender to one or
    more receivers, where each packet has a flow identifier unique to
    the flow.
 Discussion:
    The flow identifier can be an arbitrary subset of the packet
    header fields that uniquely distinguishes the flow from others.
    For example, the 5-tuple "source address; source port; destination
    address; destination port; protocol number" is commonly used for
    this purpose (where port numbers are applicable).  It is also
    possible to take advantage of the Flow Label field of IPv6
    packets.  For more comments on flow identification, refer to [6].

3.1.2. Distinguished Data Flow

 Definition:
    Distinguished data flows are flows that resource reservation
    capable routers intentionally treat better or worse than best-
    effort data flows, according to a QoS agreement defined for the
    distinguished flow.
 Discussion:
    Routers classify the packets of distinguished data flows and
    identify the data flow to which they belong.
    The most common usage of the distinguished data flow is to get
    higher-priority treatment than that of best-effort data flows (see
    the next definition).  In these cases, a distinguished data flow
    is sometimes referred to as a "premium data flow".  Nevertheless,
    theoretically it is possible to require worse treatment than that
    of best-effort flows.

Feher, et al. Informational [Page 4] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

3.1.3. Best-Effort Data Flow

 Definition:
    Best-effort data flows are flows that are not treated in any
    special manner by resource reservation capable routers; thus,
    their packets are served (forwarded) in some default way.
 Discussion:
    "Best-effort" means that the router makes its best effort to
    forward the data packet quickly and safely, but does not guarantee
    anything (e.g., delay or loss probability).  This type of traffic
    is the most common in today's Internet.
    Packets that belong to best-effort data flows need not be
    classified by the routers; that is, the routers don't need to find
    a related reservation session in order to find out to which
    treatment the packet is entitled.

3.2. Resource Reservation Protocol Basics

 This group of definitions applies to signaling-based resource
 reservation protocols implemented by IP router devices.

3.2.1. QoS Session

 Definition:
    A QoS session is an application layer concept, shared between a
    set of network nodes, that pertains to a specific set of data
    flows.  The information associated with the session includes the
    data required to identify the set of data flows in addition to a
    specification of the QoS treatment they require.
 Discussion:
    A QoS session is an end-to-end relationship.  Whenever end-nodes
    decide to obtain special QoS treatment for their data
    communication, they set up a QoS session.  As part of the process,
    they or their proxies make a QoS agreement with the network,
    specifying their data flows and the QoS treatment that the flows
    require.
    It is possible for the same QoS session to span multiple network
    domains that have different resource provisioning architectures.
    In this document, however, we only deal with the case where the
    QoS session is realized over an IntServ architecture.  It is
    assumed that sessions will be established using signaling messages
    of a resource reservation protocol.

Feher, et al. Informational [Page 5] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    QoS sessions must have unique identifiers; it must be possible to
    determine to which QoS session a given signaling message pertains.
    Therefore, each signaling message should include the identifier of
    its corresponding session.  As an example, in the case of RSVP,
    the "session specification" identifies the QoS session plus refers
    to the data flow; the "flowspec" specifies the desired QoS
    treatment and the "filter spec" defines the subset of data packets
    in the data flow that receive the QoS defined by the flowspec.
    QoS sessions can be unicast or multicast depending on the number
    of participants.  In a multicast group, there can be several data
    traffic sources and destinations.  Here the QoS agreement does not
    have to be the same for each branch of the multicast tree
    forwarding the data flow of the group.  Instead, a dedicated
    network resource in a router can be shared among many traffic
    sources from the same multicast group (cf. multicast reservation
    styles in the case of RSVP).
 Issues:
    Even though QoS sessions are considered to be unique, resource
    reservation capable routers might aggregate them and allocate
    network resources to these aggregated sessions at once.  The
    aggregation can be based on similar data flow attributes (e.g.,
    similar destination addresses) or it can combine arbitrary
    sessions as well.  While reservation aggregation significantly
    lightens the signaling processing task of a resource reservation
    capable router, it also requires the administration of the
    aggregated QoS sessions and might also lead to the violation of
    the quality guaranties referring to individual data flows within
    an aggregation [16].

3.2.2. Resource Reservation Protocol

 Definition:
    Resource reservation protocols define signaling messages and
    message processing rules used to control resource allocation in
    IntServ architectures.
 Discussion:
    It is the signaling messages of a resource reservation protocol
    that carry the information related to QoS sessions.  This
    information includes a session identifier, the actual QoS
    parameters, and possibly flow descriptors.
    The message processing rules of the signaling protocols ensure
    that signaling messages reach all network nodes concerned.  Some
    resource reservation protocols (e.g., RSVP, NSIS QoS NSLP [8]) are
    only concerned with this, i.e., carrying the QoS-related

Feher, et al. Informational [Page 6] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    information to all the appropriate network nodes, without being
    aware of its content.  This latter approach allows changing the
    way the QoS parameters are described, and different kinds of
    provisioning can be realized without the need to change the
    protocol itself.

3.2.3. Resource Reservation Capable Router

 Definition:
    A router is resource reservation capable (it supports resource
    reservation) if it is able to interpret signaling messages of a
    resource reservation protocol, and based on these messages is able
    to adjust the management of its flow classifiers and network
    resources so as to conform to the content of the signaling
    messages.
 Discussion:
    Routers capture signaling messages and manipulate reservation
    states and/or reserved network resources according to the content
    of the messages.  This ensures that the flows are treated as their
    specified QoS requirements indicate.

3.2.4. Reservation State

 Definition:
    A reservation state is the set of entries in the router's memory
    that contain all relevant information about a given QoS session
    registered with the router.
 Discussion:
    States are needed because IntServ-related resource reservation
    protocols require the routers to keep track of QoS session and
    data-flow-related metadata.  The reservation state includes the
    parameters of the QoS treatment, the description of how and where
    to forward the incoming signaling messages, refresh timing
    information, etc.
    Based on how reservation states are stored in a reservation
    capable router, the routers can be categorized into two classes:
    Hard-state resource reservation protocols (e.g., ST2 [11]) require
    routers to store the reservation states permanently, established
    by a setup signaling primitive, until the router is explicitly
    informed that the QoS session is canceled.
    There are also soft-state resource reservation capable routers,
    where there are no permanent reservation states, and each state
    has to be regularly refreshed by appropriate refresh signaling

Feher, et al. Informational [Page 7] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    messages.  If no refresh signaling message arrives during a
    certain period, then the router stops the maintenance of the QoS
    session assuming that the end-points do not intend to keep the
    session up any longer or the communication lines are broken
    somewhere along the data path.  This feature makes soft-state
    resource reservation capable routers more robust than hard-state
    routers, since no failures can cause resources to stay permanently
    stuck in the routers.  (Note that it is still possible to have an
    explicit teardown message in soft-state protocols for quicker
    resource release.)
 Issues:
    Based on the initiating point of the refresh messages, soft-state
    resource reservation protocols can be divided into two groups.
    First, there are protocols where it is the responsibility of the
    end-points or their proxies to initiate refresh messages.  These
    messages are forwarded along the path of the data flow refreshing
    the corresponding reservation states in each router affected by
    the flow.  Second, there are other protocols, where routers and
    end-points have their own schedule for the reservation state
    refreshes and they signal these refreshes to the neighboring
    routers.

3.2.5. Resource Reservation Protocol Orientation

 Definition:
    The orientation of a resource reservation protocol tells which end
    of the protocol communication initiates the allocation of the
    network resources.  Thus, the protocol can be sender- or
    receiver-oriented, depending on the location of the data flow
    source (sender) and destination (receiver) compared to the
    reservation initiator.
 Discussion:
    In the case of sender-oriented protocols (in some sources referred
    to as sender-initiated protocols), the resource reservation
    propagates in the same direction(s) as of the data flow(s).
    Consequently, in the case of receiver-oriented protocols, the
    signaling messages reserving resources are forwarded backward on
    the path of the data flow.  Due to the asymmetric routing nature
    of the Internet, in this latter case, the path of the desired data
    flow should be known before the reservation initiator would be
    able to send the resource allocation messages.  For example, in
    the case of RSVP, the RSVP PATH message, traveling from the data
    flow sources towards the destinations, first marks the path of the
    data flow on which the resource allocation messages will travel
    backward.

Feher, et al. Informational [Page 8] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    This definition considers only protocols that reserve resources
    for just one data flow between the end-nodes.  The reservation
    orientation of protocols that reserve more than one data flow is
    not defined here.
 Issues:
    The location of the reservation initiator affects the basics of
    the resource reservation protocols and therefore is an important
    aspect of characterization.  Most importantly, in the case of
    multicast QoS sessions, the sender-oriented protocols require the
    traffic sources to maintain a list of receivers and send their
    allocation messages considering the different requirements of the
    receivers.  Using multicast QoS sessions, the receiver-oriented
    protocols enable the receivers to manage their own resource
    allocation requests and thus ease the task of the sources.

3.3. Router Load Factors

    When a router is under "load", it means that there are tasks its
    CPU(s) must attend to, and/or that its memory contains data it
    must keep track of, and/or that its interface buffers are utilized
    to some extent, etc.  Unfortunately, we cannot assume that the
    full internal state of a router can be monitored during a
    benchmark; rather, we must consider the router to be a black box.
    We need to look at router "load" in a way that makes this "load"
    measurable and controllable.  Instead of focusing on the internal
    processes of a router, we will consider the external, and
    therefore observable, measurable and controllable processes that
    result in "load".
    In this section we introduce several ways of creating "load" on a
    router; we will refer to these as "load factors" henceforth.
    These load factors are defined so that they each impact the
    performance of the router in a different way (or by different
    means), by utilizing different components of a resource
    reservation capable router as separately as possible.
    During a benchmark, the performance of the device under test will
    have to be measured under different controlled load conditions,
    that is, with different values of these load factors.

3.3.1. Best-Effort Traffic Load Factor

 Definition:
    The best-effort traffic load factor is defined as the number and
    length of equal-sized best-effort data packets that traverse the
    router in a second.

Feher, et al. Informational [Page 9] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

 Discussion:
    Forwarding the best-effort data packets, which requires obtaining
    the routing information and transferring the data packet between
    network interfaces, requires processing power.  This load factor
    creates load on the CPU(s) and buffers of the router.
    For the purpose of benchmarking, we define a traffic flow as a
    stream of equal-sized packets with even interpacket delay.  It is
    possible to specify traffic with varying packet sizes as a
    superposition of multiple best-effort traffic flows as they are
    defined here.
 Issues:
    The same amount of data segmented into differently sized packets
    causes different amounts of load on the router, which has to be
    considered during benchmarking measurements.  The measurement unit
    of this load factor reflects this as well.
 Measurement unit:
    This load factor has a composite unit of [packets per second
    (pps); bytes].  For example, [5 pps; 100 bytes] means five pieces
    of one-hundred-byte packets per second.

3.3.2. Distinguished Traffic Load Factor

 Definition:
    The distinguished traffic load factor is defined as the number and
    length of the distinguished data packets that traverse the router
    in a second.
 Discussion:
    Similarly to the best-effort data, forwarding the distinguished
    data packets requires obtaining the routing information and
    transferring the data packet between network interfaces.  However,
    in this case packets have to be classified as well, which requires
    additional processing capacity.
    For the purpose of benchmarking, we define a traffic flow as a
    stream of equal-sized packets with even interpacket delay.  It is
    possible to specify traffic with varying packet sizes as a
    superposition of multiple distinguished traffic flows as they are
    defined here.
 Issues:
    Just as in the best-effort case, the same amount of data segmented
    into differently sized packets causes different amounts of load on
    the router, which has to be considered during the benchmarking

Feher, et al. Informational [Page 10] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    measurements.  The measurement unit of this load factor reflects
    this as well.
 Measurement unit:
    This load factor has a composite unit of [packets per second
    (pps); bytes].  For example, [5 pps; 100 bytes] means five pieces
    of one-hundred-byte packets per second.

3.3.3. Session Load Factor

 Definition:
    The session load factor is the number of QoS sessions the router
    is keeping track of.
 Discussion:
    Resource reservation capable routers maintain reservation states
    to keep track of QoS sessions.  Obviously, the more reservation
    states are registered with the router, the more complex the
    traffic classification becomes, and the more time it takes to look
    up the corresponding resource reservation state.  Moreover, not
    only the traffic flows, but also the signaling messages that
    control the reservation states have to be identified first, before
    taking any other action, and this kind of classification also
    means extra work for the router.
    In the case of soft-state resource reservation protocols, the
    session load also affects reservation state maintenance.  For
    example, the supervision of timers that watchdog the reservation
    state refreshes may cause further load on the router.
    This load factor utilizes the CPU(s), the main memory, and the
    session management logic (e.g., content addressable memory), if
    any, of the resource reservation capable router.
 Measurement unit:
    This load component is measured by the number of QoS sessions that
    impact the router.

3.3.4. Signaling Intensity Load Factor

 Definition:
    The signaling intensity load factor is the number of signaling
    messages that are presented at the input interfaces of the router
    during one second.
 Discussion:
    The processing of signaling messages requires processor power that
    raises the load on the control plane of the router.

Feher, et al. Informational [Page 11] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    In routers where the control plane and the data plane are not
    totally independent (e.g., certain parts of the tasks are served
    by the same processor; or the architecture has common memory
    buffers, transfer buses or any other resources) the signaling load
    can have an impact on the router's packet forwarding performance
    as well.
    Naturally, just as everywhere else in this document, the term
    "signaling messages" refer only to the resource reservation
    protocol related primitives.
 Issues:
    Most resource reservation protocols have several protocol
    primitives realized by different signaling message types.  Each of
    these message types may require a different amount of processing
    power from the router.  This fact has to be considered during the
    benchmarking measurements.
 Measurement unit:
    The unit of this factor is signaling messages/second.

3.3.5. Signaling Burst Load Factor

 Definition:
    The signaling burst load factor is defined as the number of
    signaling messages that arrive to one input port of the router
    back-to-back ([1]), causing persistent load on the signaling
    message handler.
 Discussion:
    The definition focuses on one input port only and does not
    consider the traffic arriving at the other input ports.  As a
    consequence, a set of messages arriving at different ports, but
    with such a timing that would be a burst if the messages arrived
    at the same port, is not considered to be a burst.  The reason for
    this is that it is not guaranteed in a black-box test that this
    would have the same effect on the router as a burst (incoming at
    the same interface) has.
    This definition conforms to the burst definition given in [3].
 Issues:
    Most of the resource reservation protocols have several protocol
    primitives realized by different signaling message types.  Bursts
    built up of different messages may have a different effect on the
    router.  Consequently, during measurements the content of the
    burst has to be considered as well.

Feher, et al. Informational [Page 12] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    Likewise, the first one of multiple idempotent signaling messages
    that each accomplish exactly the same end will probably not take
    the same amount of time to be processed as subsequent ones.
    Benchmarking methodology will have to consider the intended effect
    of the signaling messages, as well as the state of the router at
    the time of their arrival.
 Measurement unit:
    This load factor is characterized by the number of messages in the
    burst.

3.4. Performance Metrics

 This group of definitions is a collection of measurable quantities
 that describe the performance impact the different load components
 have on the router.
 During a benchmark, the values of these metrics will have to be
 measured under different load conditions.

3.4.1. Signaling Message Handling Time

 Definition:
    The signaling message handling time (or, in short, signal handling
    time) is the latency ([1], for store-and-forward devices) of a
    signaling message passing through the router.
 Discussion:
    The router interprets the signaling messages, acts based on their
    content and usually forwards them in an unmodified or modified
    form.  Thus the message handling time is usually longer than the
    forwarding time of data packets of the same size.
    There might be signaling message primitives, however, that are
    drained or generated by the router, like certain refresh messages.
    In this case, the signal handling time is not necessarily
    measureable, therefore it is not defined for such messages.
    In the case of signaling messages that carry information
    pertaining to multicast flows, the router might issue multiple
    signaling messages after processing them.  In this case, by
    definition, the signal handling time is the latency between the
    incoming signaling message and the last outgoing signaling message
    related to the received one.
    The signal handling time is an important characteristic as it
    directly affects the setup time of a QoS session.

Feher, et al. Informational [Page 13] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

 Issues:
    The signal handling time may be dependent on the type of the
    signaling message.  For example, it usually takes a shorter time
    for the router to remove a reservation state than to set it up.
    This fact has to be considered during the benchmarking process.
    As noted above, the first one of multiple idempotent signaling
    messages that each accomplish exactly the same end will probably
    not take the same amount of time to be processed as subsequent
    ones.  Benchmarking methodology will have to consider the intended
    effect of the signaling messages, as well as the state of the
    router at the time of their arrival.
 Measurement unit:
    The dimension of the signaling message handling time is the
    second, reported with a resolution sufficient to distinguish
    between different events/DUTs (e.g., milliseconds).  Reported
    results MUST clearly indicate the time unit used.

3.4.2. Distinguished Traffic Delay

 Definition:
    Distinguished traffic delay is the latency ([1], for store-and-
    forward devices) of a distinguished data packet passing through
    the tested router device.
 Discussion:
    Distinguished traffic packets must be classified first in order to
    assign the network resources dedicated to the flow.  The time of
    the classification is added to the usual forwarding time
    (including the queuing) that a router would spend on the packet
    without any resource reservation capability.  This classification
    procedure might be quite time consuming in routers with vast
    amounts of reservation states.
    There are routers where the processing power is shared between the
    control plane and the data plane.  This means that the processing
    of signaling messages may have an impact on the data forwarding
    performance of the router.  In this case, the distinguished
    traffic delay metric also indicates the influence the two planes
    have on each other.
 Issues:
    Queuing of the incoming data packets in routers can bias this
    metric, so the measurement procedures have to consider this
    effect.

Feher, et al. Informational [Page 14] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

 Measurement unit:
    The dimension of the distinguished traffic delay time is the
    second, reported with resolution sufficient to distinguish between
    different events/DUTs (e.g., millisecond units).  Reported results
    MUST clearly indicate the time unit used.

3.4.3. Best-effort Traffic Delay

 Definition:
    Best-effort traffic delay is the latency of a best-effort data
    packet traversing the tested router device.
 Discussion:
    If the processing power of the router is shared between the
    control and data plane, then the processing of signaling messages
    may have an impact on the data forwarding performance of the
    router.  In this case, the best-effort traffic delay metric is an
    indicator of the influence the two planes have on each other.
 Issues:
    Queuing of the incoming data packets in routers can bias this
    metric as well, so measurement procedures have to consider this
    effect.
 Measurement unit:
    The dimension of the best-effort traffic delay is the second,
    reported with resolution sufficient to distinguish between
    different events/DUTs (e.g., millisecond units).  Reported results
    MUST clearly indicate the time unit used.

3.4.4. Signaling Message Deficit

 Definition:
    Signaling message deficit is one minus the ratio of the actual and
    the expected number of signaling messages leaving a resource
    reservation capable router.
 Discussion:
    This definition gives the same value as the ratio of the lost
    (that is, not forwarded or not generated) and the expected
    messages.  The above calculation must be used because the number
    of lost messages cannot be measured directly.
    There are certain types of signaling messages that reservation
    capable routers are required to forward as soon as their
    processing is finished.  However, due to lack of resources or
    other reasons, the forwarding or even the processing of these
    signaling messages might not take place.

Feher, et al. Informational [Page 15] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    Certain other kinds of signaling messages must be generated by the
    router in the absence of any corresponding incoming message.  It
    is possible that an overloaded router does not have the resources
    necessary to generate such a message.
    To characterize these situations we introduce the signaling
    message deficit metric that expresses the ratio of the signaling
    messages that have actually left the router and those ones that
    were expected to leave the router.  We subtract this ratio from
    one in order to obtain a loss-type metric instead of a "message
    survival metric".
    Since the most frequent reason for signaling message deficit is
    high router load, this metric is suitable for sounding out the
    scalability limits of resource reservation capable routers.
    During the measurements one must be able to determine whether a
    signaling message is still in the queues of the router or if it
    has already been dropped.  For this reason we define a signaling
    message as lost if no forwarded signaling message is emitted
    within a reasonably long time period.  This period is defined
    along with the benchmarking methodology.
 Measurement unit:
    This measure has no unit; it is expressed as a real number, which
    is between zero and one, including the limits.

3.4.5. Session Maintenance Capacity

 Definition:
    The session maintenance capacity metric is used in the case of
    soft-state resource reservation protocols only.  It is defined as
    the ratio of the number of QoS sessions actually being maintained
    and the number of QoS sessions that should have been maintained.
 Discussion:
    For soft-state protocols maintaining a QoS session means
    refreshing the reservation states associated with it.
    When a soft-state resource reservation capable router is
    overloaded, it may happen that the router is not able to refresh
    all the registered reservation states, because it does not have
    the time to run the state refresh task.  In this case, sooner or
    later some QoS sessions will be lost even if the endpoints still
    require their maintenance.

Feher, et al. Informational [Page 16] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    The session maintenance capacity sounds out the maximal number of
    QoS sessions that the router is capable of maintaining.
 Issues:
    The actual process of session maintenance is protocol and
    implementation dependent, thus so is the method to examine whether
    a session is maintained or not.
    In the case of soft-state resource reservation protocols, where
    the network nodes are responsible for generating the refresh
    messages, a router that fails to maintain a QoS session may not
    emit refresh signaling messages either.  This has direct
    consequences on the signaling message deficit metric.
 Measurement unit:
    This measure has no unit; it is expressed as a real number, which
    is between zero and one (including the limits).

3.5. Router Load Conditions and Scalability Limit

 Depending mainly, but not exclusively, on the overall load of a
 router, it can be in exactly one of the following four conditions at
 a time: loss-free and QoS compliant; lossy and QoS compliant; loss-
 free but not QoS compliant; and neither loss-free nor QoS compliant.
 These conditions are defined below, along with the scalability limit.

3.5.1. Loss-Free Condition

 Definition:
    A router is in loss-free condition, or loss-free state, if and
    only if it is able to perform its tasks correctly and in a timely
    fashion.
 Discussion:
    All existing routers have finite buffer memory and finite
    processing power.  If a router is in loss-free state, the buffers
    of the router still contain enough free space to accommodate the
    next incoming packet when it arrives.  Also, the router has enough
    processing power to cope with all its tasks, thus all required
    operations are carried out within the time the protocol
    specification allows; or, if this time is not specified by the
    protocol, then in "reasonable time" (which is then defined in the
    benchmarks).  Similar considerations can be applied to other
    resources a router may have, if any; in loss-free states, the
    utilization of these resources still allows the router to carry
    out its tasks in accordance with applicable protocol
    specifications and in "reasonable time".

Feher, et al. Informational [Page 17] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    Note that loss-free states as defined above are not related to the
    reservation states of resource reservation protocols.  The word
    "state" is used to mean "condition".
    Also note that it is irrelevant what internal reason causes a
    router to fail to perform in accordance with protocol
    specifications or in "reasonable time"; if it is not high load but
    -- for example -- an implementation error that causes the device
    to perform inadequately, it still cannot be said to be in a loss-
    free state.  The same applies to the random early dropping of
    packets in order to prevent congestion.  In a black-box
    measurement it is impossible to determine whether a packet was
    dropped as part of a congestion control mechanism or because the
    router was unable to forward it; therefore, if packet loss is
    observed except as noted below, the router is by definition in
    lossy state (lossy condition).
    If a distinguished data flow exceeds its allotted bandwidth, it is
    acceptable for routers to drop excess packets.  Thus, a router
    that is QoS Compliant (see below) is also loss-free provided that
    it only drops packets from distinguished data flows.
    If a device is not in a loss-free state, it is in a lossy
    condition/state.
 Related definitions:
    Lossy Condition
    QoS Compliant Condition
    Not QoS Compliant Condition
    Scalability Limit

3.5.2. Lossy Condition

 Definition:
    A router is in a lossy condition, or lossy state, if it cannot
    perform its duties adequately for some reason; that is, if it does
    not meet protocol specifications (except QoS guarantees, which are
    treated separately), or -- if time-related specifications are
    missing -- doesn't complete some operations in "reasonable time"
    (which is then defined in the benchmarks).
 Discussion:
    A router may be in a lossy state for several reasons, including
    but not necessarily limited to the following:
    a) Buffer memory has run out, so either an incoming or a buffered
       packet has to be dropped.

Feher, et al. Informational [Page 18] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    b) The router doesn't have enough processing power to cope with
       all its duties.  Some required operations are skipped, aborted
       or suffer unacceptable delays.
    c) Some other finite internal resource is exhausted.
    d) The router runs a defective (non-conforming) protocol
       implementation.
    e) Hardware malfunction.
    f) A congestion control mechanism is active.
    Loss can mean the loss of data packets as well as signaling
    message deficit.
    A router that does not lose data packets and does not experience
    signaling message deficit but fails to meet required QoS
    parameters is in the loss-free, but not in the QoS compliant
    state.
    If a device is not in a lossy state, it is in a loss-free
    condition/state.
 Related definitions:
    Loss-Free Condition (especially the discussion of congestion
       control mechanisms that cause packet loss)
    Scalability Limit
    Signaling Message Deficit
    QoS Compliant Condition
    Not QoS Compliant Condition

3.5.3. QoS Compliant Condition

 Definition:
    A router is in the QoS compliant state if and only if all
    distinguished data flows receive the QoS treatment they are
    entitled to.
 Discussion:
    Defining what specific QoS guarantees must be upheld is beyond the
    scope of this document because every reservation model may specify
    a different set of such parameters.
    Loss, delay, jitter etc. of best-effort data flows are irrelevant
    when considering whether a router is in the QoS compliant state.

Feher, et al. Informational [Page 19] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

 Related definitions:
    Loss-Free Condition
    Lossy Condition
    Not QoS Compliant Condition
    Scalability Limit

3.5.4. Not QoS Compliant Condition

 Definition:
    A router is in the not QoS compliant state if and only if it is
    not in the QoS compliant condition.
 Related definitions:
    Loss-Free Condition
    Lossy Condition
    QoS Compliant Condition
    Scalability Limit

3.5.5. Scalability Limit

 Definition:
    The scalability limits of a router are the boundary load
    conditions where the router is still in the loss-free and QoS
    compliant state, but the smallest amount of additional load would
    drive it to a state that is either QoS compliant but not loss-
    free, or not QoS compliant but loss-free, or neither loss-free nor
    QoS compliant.
 Discussion:
    An unloaded router that operates correctly is in a loss-free and
    QoS compliant state.  As load increases, the resources of the
    router are becoming more and more utilized.  At a certain point,
    the router enters a state that is either not QoS compliant, or not
    loss-free, or neither QoS compliant nor loss-free.  Note that such
    a point may be impossible to reach in some cases (for example if
    the bandwidth of the physical medium prevents increasing the
    traffic load any further).
    A particular load condition can be identified by the corresponding
    values of the load factors (as defined in 3.3 Router Load Factors)
    impacting the router.  These values can be represented as a 7-
    tuple of numbers (there are only five load factors, but the
    traffic load factors have composite units and thus require two
    numbers each to express).  We can think of these tuples as vectors
    that correspond to a state that is either both loss free and QoS
    compliant, or not loss-free (but QoS compliant), or not QoS
    compliant (but loss-free), or neither loss-free nor QoS compliant.
    The scalability limit of the router is, then, the boundary between

Feher, et al. Informational [Page 20] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

    the sets of vectors corresponding to the loss-free and QoS
    compliant states and all other states.  Finding these boundary
    points is one of the objectives of benchmarking.
    Benchmarks may try to separately identify the boundaries of the
    loss-free and of the QoS compliant conditions in the (seven-
    dimensional) space defined by the load-vectors.
 Related definitions:
    Lossy Condition
    Loss-Free Condition
    QoS Compliant Condition
    Non QoS Compliant Condition

4. Security Considerations

 As this document only provides terminology and does not describe a
 protocol, an implementation, or a procedure, there are no security
 considerations associated with it.

5. Acknowledgements

 We would like to thank Telia Research AB, Sweden and the High Speed
 Networks Laboratory at the Department of Telecommunication and Media
 Informatics of the Budapest University of Technology and Economics,
 Hungary for their support in the research and development work, which
 contributed to the creation of this document.

6. References

6.1. Normative References

 [1]  Bradner, S., "Benchmarking Terminology for Network
      Interconnection Devices", RFC 1242, July 1991.
 [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [3]  Mandeville, R., "Benchmarking Terminology for LAN Switching
      Devices", RFC 2285, February 1998.

6.2. Informative References

 [4]  Braden, R., Clark, D., and S. Shenker, "Integrated Services in
      the Internet Architecture: an Overview", RFC 1633, June 1994.

Feher, et al. Informational [Page 21] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

 [5]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
      Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
      Functional Specification", RFC 2205, September 1997.
 [6]  Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
      Bosch, "Next Steps in Signaling (NSIS): Framework", RFC 4080,
      June 2005.
 [7]  Schulzrinne, H. and R. Hancock, "GIST:  General Internet
      Signaling Transport", Work in Progress, April 2007.
 [8]  Manner, J., Ed., Karagiannis, G., and A. McDonald, "NSLP for
      Quality-of-Service Signaling", Work in Progress, June 2007.
 [9]  Ash, J., Bader, A., Kappler, C., and D. Oran, "QoS NSLP QSPEC
      Template", Work in Progress, March 2007.
 [10] P. Pan, H. Schulzrinne, "YESSIR: A Simple Reservation Mechanism
      for the Internet", Computer Communication Review, on-line
      version, volume 29, number 2, April 1999
 [11] Delgrossi, L. and L. Berger, "Internet Stream Protocol Version 2
      (ST2) Protocol Specification - Version ST2+", RFC 1819, August
      1995.
 [12] P. White, J. Crowcroft, "A Case for Dynamic Sender-Initiated
      Reservation in the Internet", Journal on High Speed Networks,
      Special Issue on QoS Routing and Signaling, Vol. 7 No. 2, 1998
 [13] J. Bergkvist, D. Ahlard, T. Engborg, K. Nemeth, G. Feher, I.
      Cselenyi, M. Maliosz, "Boomerang : A Simple Protocol for
      Resource Reservation in IP Networks", Vancouver, IEEE Real-Time
      Technology and Applications Symposium, June 1999
 [14] A. Eriksson, C. Gehrmann, "Robust and Secure Light-weight
      Resource Reservation for Unicast IP Traffic", International WS
      on QoS'98, IWQoS'98, May 18-20, 1998
 [15] Manner, J. and X. Fu, "Analysis of Existing Quality-of-Service
      Signaling Protocols", RFC 4094, May 2005.
 [16] Baker, F., Iturralde, C., Le Faucheur, F., and B. Davie,
      "Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC 3175,
      September 2001.

Feher, et al. Informational [Page 22] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

Authors' Addresses

 Gabor Feher
 Budapest University of Technology and Economics
 Department of Telecommunications and Media Informatics
 Magyar Tudosok krt. 2, H-1117, Budapest, Hungary
 Phone: +36 1 463-1538
 EMail: Gabor.Feher@tmit.bme.hu
 Krisztian Nemeth
 Budapest University of Technology and Economics
 Department of Telecommunications and Media Informatics
 Magyar Tudosok krt. 2, H-1117, Budapest, Hungary
 Phone: +36 1 463-1565
 EMail: Krisztian.Nemeth@tmit.bme.hu
 Andras Korn
 Budapest University of Technology and Economics
 Department of Telecommunication and Media Informatics
 Magyar Tudosok krt. 2, H-1117, Budapest, Hungary
 Phone: +36 1 463-2664
 EMail: Andras.Korn@tmit.bme.hu
 Istvan Cselenyi
 TeliaSonera International Carrier
 Vaci ut 22-24, H-1132 Budapest, Hungary
 Phone: +36 1 412-2705
 EMail: Istvan.Cselenyi@teliasonera.com

Feher, et al. Informational [Page 23] RFC 4883 Benchmarking Terms for RR Capable Routers July 2007

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 contained in BCP 78, and except as set forth therein, the authors
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Feher, et al. Informational [Page 24]

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