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RFC 1677 - Tactical Radio Frequency Communication Requirements f


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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.

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

   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

   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.

   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

   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.

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,

   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.

   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

 

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