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rfc:rfc1677

Network Working Group B. Adamson Request for Comments: 1677 Naval Research Laboratory Category: Informational August 1994

    Tactical Radio Frequency Communication Requirements for IPng

Status of this Memo

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

Abstract

 This document was submitted to the IETF IPng area in response to RFC
 1550.  Publication of this document does not imply acceptance by the
 IPng area of any ideas expressed within.  Comments should be
 submitted to the big-internet@munnari.oz.au mailing list.

Executive Summary

 The U.S. Navy has several efforts exploring the applicability of
 commercial internetworking technology to tactical RF networks.  Some
 these include the NATO Communication System Network Interoperability
 (CSNI) project, the Naval Research Laboratory Data/Voice Integration
 Advanced Technology Demonstration (D/V ATD), and the Navy
 Communication Support System (CSS) architecture development.
 Critical requirements have been identified for security, mobility,
 real-time data delivery applications, multicast, and quality-of-
 service and policy based routing.  Address scaling for Navy
 application of internet technology will include potentially very
 large numbers of local (intra-platform) distributed information and
 weapons systems and a smaller number of nodes requiring global
 connectivity.  The flexibility of the current Internet Protocol (IP)
 for supporting widely different communication media should be
 preserved to meet the needs of the highly heterogeneous networks of
 the tactical environment.  Compact protocol headers are necessary for
 efficient data transfer on the relatively-low throughput RF systems.
 Mechanisms which can  enhance the effectiveness of an internet
 datagram protocol to provide resource reservation, priority, and
 service quality guarantees are also very important.  The broadcast
 nature of many RF networks and the need for broad dissemination of
 information to warfighting participants makes multicast the general
 case for information flow in the tactical environment.

Adamson [Page 1] RFC 1677 IPng Tactical RF Requirements August 1994

Background

 This paper describes requirements for Internet Protocol next
 generation (IPng) candidates with respect to their application to
 military tactical radio frequency (RF) communication networks.  The
 foundation for these requirements are experiences in the NATO
 Communication System Network Interoperability (CSNI) project, the
 Naval Research Laboratory Data/Voice Integration Advanced Technology
 Demonstration (D/V ATD), and the Navy Communication Support System
 (CSS) architecture development.
 The goal of the CSNI project is to apply internetworking technology
 to facilitate multi-national interoperability for typical military
 communication applications (e.g., electronic messaging, tactical data
 exchange, and digital voice) on typical tactical RF communication
 links and networks.  The International Standard Organization (ISO)
 Open Systems Interconnect (OSI) protocol suite, including the
 Connectionless Network Protocol (CLNP), was selected for this project
 for policy reasons.  This paper will address design issues
 encountered in meeting the project goals with this particular
 protocol stack.
 The D/V ATD is focused on demonstrating  a survivable, self-
 configuring, self-recovering RF subnetwork technology capable of
 simultaneously supporting data delivery, including message transfer,
 imagery, and tactical data, and real-time digital voice applications.
 Support for real-time interactive communication applications was
 extended to include a "white board" and other similar applications.
 IP datagram delivery is also planned as part of this demonstration
 system.
 The CSS architecture will provide U.S. Navy tactical platforms with a
 broad array of user-transparent voice and data information exchange
 services.  This will include support for sharing and management of
 limited platform communication resources among multiple warfighting
 communities.  Emphasis is placed on attaining interoperability with
 other military services and foreign allies.  Utilization of
 commercial off-the-shelf communications products to take advantage of
 existing economies of scale is important to make any resulting system
 design affordable.  It is anticipated that open, voluntary standards,
 and flexible communication protocols, such as IP, will play a key
 role in meeting the goals of this architecture.

Introduction

 Before addressing any IPng requirements as applied to tactical RF
 communications, it is necessary to define what this paper means by
 "IPng requirements".  To maintain brevity, this paper will focus on

Adamson [Page 2] RFC 1677 IPng Tactical RF Requirements August 1994

 criteria related specifically to the design of an OSI model's Layer 3
 protocol format and a few other areas suggested by RFC 1550.  There
 are several additional areas of concern in applying internetwork
 protocols to the military tactical RF setting including routing
 protocol design, address assignment, network management, and resource
 management.  While these areas are equally important, this paper will
 attempt to satisfy the purpose of RFC 1550 and address issues more
 directly applicable to selection of an IPng candidate.

Scaling

 The projection given in RFC 1550 that IPng should be able to deal
 with 10 to the 12th nodes is more than adequate in the face of
 military requirements.  More important is that it is possible to
 assign addresses efficiently.  For example, although a military
 platform may have a relatively small number of nodes with
 requirements to communicate with a larger, global infrastructure,
 there will likely be applications of IPng to management and control
 of distributed systems (e.g., specific radio communications equipment
 and processors, weapons systems, etc.) within the platform.  This
 local expansion of address space requirements may not necessarily
 need to be solved by "sheer numbers" of globally-unique addresses but
 perhaps by alternate delimitation of addressing to differentiate
 between globally-unique and locally-unique addressing.  The
 advantages of a compact internet address header are clear for
 relatively low capacity RF networks.

Timescale, Transition and Deployment

 The U.S. Navy and other services are only recently (the last few
 years) beginning to design and deploy systems utilizing open systems
 internetworking technology.  From this point of view, the time scale
 for selection of IPng must be somewhat rapid.  Otherwise, two
 transition phases will need to be suffered, 1) the move from unique,
 "stove pipe" systems to open, internetworked (e.g., IP) systems, and
 then 2) a transition from deployed IP-based systems to IPng.  In some
 sense, if an IPng is quickly accepted and widely implemented, the
 transition for tactical military systems will be somewhat easier than
 the enterprise Internet where a large investment in current IP
 already exists.  However, having said this, the Department of Defense
 as a whole already deploys a large number  of IP-capable systems, and
 the issue of transition from IP to IPng remains significant.

Security

 As with any military system, information security, including
 confidentiality and authenticity of data, is of paramount importance.
 With regards to IPng, network layer security mechanisms for tactical

Adamson [Page 3] RFC 1677 IPng Tactical RF Requirements August 1994

 RF networks generally important for authentication purposes,
 including routing protocol authentication, source authentication, and
 user network access control.  Concerns for denial of service attacks,
 traffic analysis monitoring, etc., usually dictate that tactical RF
 communication networks provide link layer security mechanisms.
 Compartmentalization and multiple levels of security for different
 users of common communication resources call for additional security
 mechanisms at the transport layer or above.  In the typical tactical
 RF environment, network layer confidentiality and, in some cases,
 even authentication becomes redundant with these other security
 mechanisms.
 The need for network layer security mechanisms becomes more critical
 when the military utilizes commercial telecommunications systems or
 has tactical systems inter-connected with commercial internets.
 While the Network Encryption Server (NES) works in this role today,
 there is a desire for a more integrated, higher performance solution
 in the future.  Thus, to meet the military requirement for
 confidentiality and authentication, an IPng candidate must be capable
 of operating in a secure manner when necessary, but also allow for
 efficient operation on low-throughput RF links when other security
 mechanisms are already in place.
 In either of these cases, key management is extremely important.
 Ideally, a common key management system could be used to provide key
 distribution for security mechanisms at any layer from the
 application to the link layer.  As a result, it is anticipated,
 however, that key distribution is a function of management, and
 should not dependent upon a particular IPng protocol format.

Mobility

 The definition of most tactical systems include mobility in some
 form.  Many tactical RF network designs provide means for members to
 join and leave particular RF subnets as their position changes.  For
 example, as a platform moves out of the RF line-of-sight (LOS) range,
 it may switch from a typical LOS RF media such as the ultra-high
 frequency (UHF) band to a long-haul RF media such as high frequency
 (HF) or satellite communication (SATCOM).
 In some cases, such as the D/V ATD network, the RF subnet will
 perform its own routing and management of this dynamic topology.
 This will be invisible to the internet protocol except for
 (hopefully) subtle changes to some routing metrics (e.g., more or
 less delay to reach a host).  In this instance, the RF subnetwork
 protocols serve as a buffer to the internet routing protocols and
 IPng will not need to be too concerned with mobility.

Adamson [Page 4] RFC 1677 IPng Tactical RF Requirements August 1994

 In other cases, however, the platform may make a dramatic change in
 position and require a major change in internet routing.  IPng must
 be able to support this situation.  It is recognized that an internet
 protocol may not be able to cope with large, rapid changes in
 topology.  Efforts will be made to minimize the frequency of this in
 a tactical RF communication architecture, but there are instances
 when a major change in topology is required.
 Furthermore, it should be realized that mobility in the tactical
 setting is not limited to individual nodes moving about, but that, in
 some cases, entire subnetworks may be moving.  An example of this is
 a Navy ship with multiple LANs on board, moving through the domains
 of different RF networks.  In some cases, the RF subnet will be
 moving, as in the case of an aircraft strike force, or Navy
 battlegroup.

Flows and Resource Reservation

 The tactical military has very real requirements for multi-media
 services across its shared and inter-connected RF networks.  This
 includes applications from digital secure voice integrated with
 applications such as "white boards" and position reporting for
 mission planning purposes to low-latency, high priority tactical data
 messages (target detection, identification, location and heading
 information).  Because of the limited capacity of tactical RF
 networks, resource reservation is extremely important to control
 access to these valuable resources.  Resource reservation can play a
 role in "congestion avoidance" for these limited resources as well as
 ensuring that quality-of-service data delivery requirements are met
 for multi-media communication.
 Note there is more required here than can be met by simple quality-
 of-service (QoS) based path selection and subsequent source-routing
 to get real-time data such as voice delivered.  For example, to
 support digital voice in the CSNI project, a call setup and resource
 reservation protocol was designed.  It was determined that the QoS
 mechanisms provided by the CLNP specification were not sufficient for
 our voice application path selection.  Voice calls could not be
 routed and resources reserved based on any single QoS parameter
 (e.g., delay, capacity, etc.) alone.  Some RF subnets in the CSNI
 test bed simply did not have the capability to support voice calls.
 To perform resource reservation for the voice calls, the CLNP cost
 metric was "hijacked" as essentially a Type of Service identifier to
 let the router know which datagrams were associated with a voice
 call.  The cost metric, concatenated with the source and destination
 addresses were used to form a unique identifier for voice calls in
 the router and subnet state tables.  Voice call paths were to be
 selected by the router (i.e. the "cost" metric was calculated) as a

Adamson [Page 5] RFC 1677 IPng Tactical RF Requirements August 1994

 rule-based function of each subnet's capability to support voice, its
 delay, and its capacity.  While source routing provided a possible
 means for voice datagrams to find their way from router to router,
 the network address alone was not explicit enough to direct the data
 to the correct interface, particularly in cases where there were
 multiple communication media interconnecting two routers along the
 path.  Fortunately, exclusive use of the cost QoS indicator for voice
 in CSNI was able to serve as a flag to the router for packets
 requiring special handling.
 While a simple Type of Service field as part of an IPng protocol can
 serve this purpose where there are a limited number of well known
 services (CSNI has a single special service - 2400 bps digital
 voice), a more general technique such as RSVP's Flow Specification
 can support a larger set of such services.  And a field, such as the
 one sometimes referred to as a Flow Identification (Flow ID), can
 play an important role in facilitating inter-networked data
 communication over these limited capacity networks.
 For example, the D/V ATD RF sub-network provides support for both
 connectionless datagram delivery and virtual circuit connectivity.
 To utilize this capability, an IPng could establish a virtual circuit
 connection across this RF subnetwork which meets the requirements of
 an RSVP Flow Specification. By creating an association between a
 particular Flow ID and the subnetwork header identifying the
 established virtual circuit, an IPng gateway could forward data
 across the low-capacity while removing most, if not all, of the IPng
 packet header information.  The receiving gateway could re- construct
 these fields based on the Flow Specification of the particular Flow
 ID/virtual circuit association.
 In summary, a field such as a Flow Identification can serve at least
 two important purposes:
       1)      It can be used by routers (or gateways) to identify
               packets with special, or pre-arranged delivery
               requirements.  It is important to realize that it may
               not always be possible to "peek" at internet packet
               content for this information if certain security
               considerations are met (e.g., an encrypted transport
               layer).
       2)      It can aid mapping datagram services to different
               types of communication services provided by
               specialized subnet/data link layer protocols.

Adamson [Page 6] RFC 1677 IPng Tactical RF Requirements August 1994

Multicast

 Tactical military communication has a very clear requirement for
 multicast.  Efficient dissemination of information to distributed
 warfighting participants can be the key to success in a battle.  In
 modern warfare, this information includes imagery, the "tactical
 scene" via tactical data messages, messaging information, and real-
 time interactive applications such as digital secure voice.  Many of
 the tactical RF communication media are broadcast by nature, and
 multicast routing can take advantage of this topology to distribute
 critical data to a large number of participants.  The throughput
 limitations imposed by these RF media and the physics of potential
 electronic counter measures (ECM) dictate that this information be
 distributed efficiently.  A multicast architecture is the general
 case for information flow in a tactical internetwork.

Quality of Service and Policy-Based Routing

 Quality of service and policy based routing are of particular
 importance in a tactical environment with limited communication
 resources, limited bandwidth, and possible degradation and/or denial
 of service.  Priority is a very important criteria in the tactical
 setting.  In the tactical RF world of limited resources (limited
 bandwidth, radio assets, etc.) there will be instances when there is
 not sufficient capacity to provide all users with their perception of
 required communication capability.  It is extremely important for a
 shared, automated communication system to delegate capacity higher
 priority users.  Unlike the commercial world, where everyone has a
 more equal footing, it is possible in the military environment to
 assign priority to users or even individual datagrams.  An example of
 this is the tactical data exchange.  Tactical data messages are
 generally single-datagram messages containing information on the
 location, bearing, identification, etc., of entities detected by
 sensors.  In CSNI, tactical data messages were assigned 15 different
 levels of CLNP priority.  This ensured that important messages, such
 as a rapidly approaching enemy missile's trajectory, were given
 priority over less important messages, such as a friendly, slow-
 moving tanker's heading.

Applicability

 There will be a significant amount of applicability to tactical RF
 networks.  The current IP and CLNP protocols are being given
 considerable attention in the tactical RF community as a means to
 provide communication interoperability across a large set of
 heterogeneous RF networks in use by different services and countries.
 The applicability of IPng can only improve with the inclusion of
 features critical to supporting QoS and Policy based routing,

Adamson [Page 7] RFC 1677 IPng Tactical RF Requirements August 1994

 security, real-time multi-media data delivery, and extended
 addressing.  It must be noted that it is very important that the IPng
 protocol headers not grow overly large.  There is a sharp tradeoff
 between the value added by these headers (interoperability, global
 addressing, etc.) and the degree of communication performance
 attainable on limited capacity RF networks.  Regardless of the data
 rate that future RF networks will be capable of supporting, there is
 always a tactical advantage in utilizing your resources more
 efficiently.

Datagram Service

 The datagram service paradigm provides many useful features for
 tactical communication networks.  The "memory" provided by datagram
 headers, provides an inherent amount of survivability essential to
 the dynamics of the tactical communication environment.  The
 availability of platforms for routing and relaying is never 100%
 certain in a tactical scenario.  The efficiency with which multi-cast
 can be implemented in a connectionless network is highly critical in
 the tactical environment where rapid, efficient information
 dissemination can be a deciding factor.  And, as has been proven,
 with several different Internet applications and experiments, a
 datagram service is capable of providing useful connection-oriented
 and real-time communication services.
 Consideration should be given in IPng to how it can co-exist with
 other architectures such as switching fabrics which offer demand-
 based control over topology and connectivity.  The military owns many
 of its own communication resources and one of the large problems in
 managing the military communication infrastructure is directing those
 underlying resources to where they are needed.  Traditional
 management (SNMP, etc.) is of course useful here, but RF
 communication media can be somewhat dynamically allocated.  Circuit
 switching designs offer some advantages here.  Dial-up IP routing is
 an example of an integrated solution.  The IPng should be capable of
 supporting a similar type of operation.

Support of Communication Media

 The tactical communication environment includes a very broad spectrum
 of communication media from shipboard fiber-optic LANs to very low
 data rate (<2400 bps) RF links.  Many of the RF links, even higher
 speed ones, can exhibit error statistics not necessarily well-
 serviced by higher layer reliable protocols (i.e., TCP).  In these
 cases, efficient lower layer protocols can be implemented to provide
 reliable datagram delivery at the link layer, but at the cost of
 highly variable delay performance.

Adamson [Page 8] RFC 1677 IPng Tactical RF Requirements August 1994

 It is also important to recognize that RF communication cannot be
 viewed from the IPng designer as simple point-to-point  links.
 Often, highly complex, unique subnetwork protocols are utilized to
 meet requirements of survivability, communications performance with
 limited bandwidth, anti- jam and/or low probability of detection
 requirements.  In some of these cases IPng will be one of several
 Layer 3 protocols sharing the subnetwork.
 It is understood that IPng cannot be the panacea of Layer 3
 protocols, particularly when it comes to providing special mechanisms
 to support the endangered-specie low data rate user.  However, note
 that there are many valuable low data rate applications useful to the
 tactical user.  And low user data rates, coupled with efficient
 networking protocols can allow many more users share limited RF
 bandwidth.  As a result, any mechanisms which facilitate compression
 of network headers can be considered highly valuable in an IPng
 candidate.

Security Considerations

 Security issues are discussed throughout this memo.

Author's Address

 R. Brian Adamson
 Communication Systems Branch
 Information Technology Division
 Naval Research Laboratory
 NRL Code 5523
 Washington, DC 20375
 EMail: adamson@itd.nrl.navy.mil

Adamson [Page 9]

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