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- Network Working Group B. Adamson
- Request for Comments: 1677 Naval Research Laboratory
- Category: Informational August 1994
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- Tactical Radio Frequency Communication Requirments 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.
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- Adamson [Page 1]
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- RFC 1677 IPng Tactical RF Requirements August 1994
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- 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
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- Adamson [Page 2]
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- RFC 1677 IPng Tactical RF Requirements August 1994
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- 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
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- Adamson [Page 3]
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- RFC 1677 IPng Tactical RF Requirements August 1994
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- 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.
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- Adamson [Page 4]
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- RFC 1677 IPng Tactical RF Requirements August 1994
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- 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
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- Adamson [Page 5]
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- RFC 1677 IPng Tactical RF Requirements August 1994
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- 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.
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- Adamson [Page 6]
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- RFC 1677 IPng Tactical RF Requirements August 1994
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- 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,
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- Adamson [Page 7]
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- RFC 1677 IPng Tactical RF Requirements August 1994
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- 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.
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- Adamson [Page 8]
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- RFC 1677 IPng Tactical RF Requirements August 1994
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- 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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