Internet DRAFT - draft-adamson-radio-req
draft-adamson-radio-req
INTERNET DRAFT
<draft-adamson-ipng-radio-req-00.txt>
IPng White Paper: TACTICAL RADIO FREQUENCY COMMUNICATION REQUIREMENTS
FOR NEXT GENERATION INTERNET PROTOCOLS
R. Brian Adamson Communication Systems Branch
<adamson@itd.nrl.navy.mil> Information Technology Division
8 April 1994 Naval Research Laboratory
STATUS OF THIS REPORT
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.
Distribution of this memo is unlimited.
This document is an Internet Draft. Internet Drafts are working
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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.
2 (IPng Tactical Requirements)
REQUIREMENTS
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.
3 (IPng Tactical Requirements)
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.
4 (IPng Tactical Requirements)
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.
5 (IPng Tactical Requirements)
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.
6 (IPng Tactical Requirements)
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.
7 (IPng Tactical Requirements)
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.
8 (IPng Tactical Requirements)
Brian
___________________________________________________________________
R. Brian Adamson Information Technology Division
adamson@itd.nrl.navy.mil Naval Research Laboratory
NRL Code 5523 Washington, DC 20375
Expire: September 1994
