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 RFC1550. 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 RFC1550 and address issues more
directly applicable to selection of an IPng candidate.
Scaling
The projection given in RFC1550 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
