MIL:COMP:NET: Internetworking in the Navy

Eugene Leitl (
Sun, 18 May 1997 17:10:49 +0200 (MET DST)


by way of an apology:
why this particular bioOCR'd piece? partly dire
gore-crowing, partly _unhealthy_ fascination with
bleeding-edge killer applications, a (surely)
perverse wish to elucidate some (possibly hidden)
agendas on behalf of IPng definition, partly an
attempt to forecast the outlines of the shape of
possible future conflicts (so at least you can
classify what had hit you ;), partly an attempt
to extract also civ-relevant tech info. All in all,
pretty perfectly acceptable reasons, imo...

ciao, 'gene

Internetworking in the Navy -- R. Brian Adamson, Naval
Research Laboratory (Excerpted from "IPng Internet
Protocol Next Generation", Scott O. Bradner, Allison
Mankin, ed., Addision Wesley, 1996, pp. 27-35.).

The U.S. Navy and other armed services have identified
critical requirements for security, mobility, real-time
data-delivery applications, multicast, and
quality-of-service and policy-based routing of the next
generation of the Internet Protocol. Address scaling
for military application of internet technology may
include very large numbers of local (interplatform)
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 meed the needs of the highly
heterogenous networks of the tactical environment.

Compact protocol headers are necessary for efficient
data transfer on the relatively low throughput radio
frequency (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 war-fighting
participants makes multicast the general case for
information flow in the tactical environment.

<b>Naval Research Efforts.</b> The requirements for
the Internet protocol next generation (IPng) candidates
with respect to their application to military tactical
RF communication networks need to be considered along
with private concerns. The foundatons for these
requirements are experiences born of the Navy's
research efforts in this area: 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

<b>NATO Communication System Network Interoperability
Project.</b> The goal of the CSNI project is to apply
internetworking technology to facilitate multinational
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. There are design issues in meeting
the project goals with this particular protocol stack.

<b>Naval Research Laboratory's Data/Voice Integration
advanced Technology Demonstration.</b> 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, tactical data, and
real-time digital voice applications. Support for
real-time interactive communication application was
extended to include a "white board" and other similiar
applications. IP datagram delivery is also planned
as part of this demonstration system.

<b>Navy Communication Support System Architecture
Development.</b> 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 communicaiton resources
among multiple war-fighting communities. Emphasis is
placed on attaining interoperability of with other
military services and foreign allies. Utilization of
commercial off-the-shelf communication 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.

<b>IPng Requirements and RFC-1550.</b> Before
addressing and IPng requirements as applied to
tactical RF comminications, it is necessary to
define what is meant by "IPng requirements".
To maintain brevity, the criteria described in
this section are specifically related to the
design of an OSI model's Layer 3 protocol format
and a few other areas suggested by RFC-1550.
There are also several additional areas of
concern in applying intrenetwork protocols to
the military tactical RF setting:

* routing protocol design
* address assignment
* network management
* resource management

<i>Scale.</i> The requirement that IPng should be
able to deal with 10^12 nodes {{hah! never heard of
nanotechnology, apparently. why do we never learn?}}
is more than adequate in the face of military
requirements. More importantly, with IPng it must be
possible to assign adresses 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 be likely applications of IPng to
management and control of distributed systems
(e.g., specific radio communications equipement
and processors, weapon systems) 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
delimitations of addressing to differentiate between
globally unique and localy unique addressing. The
advantages of a compact internet address header
are clear for relatively low capacity RF networks.

<i>Transition.</i> The Navy and other armed
services are currently (in the past few years)
designing and deploying systems that use open
networking technology. From this point of view,
the time scale for selecting 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 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.

<i>Media Independence.</i> The tactical communication
environment includes a very broad spectrum {{spread-spectrum?
;) }} of communication media from shipboard fiber-optic
LANs to very low data rate (fewer than 2400 bps) RF links.
Many of the RF links, evne higher speed ones, can exhibit
error statistics not necessarily well-serviced by higher
layre 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 bandwith,
anti-jam, and/or low probability of detection

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-species low data rate
user. In some of these cases IPng will be one of several
Layer 3 protocols sharing the subnetwork. However, note
that there are potentially many low date rate, IP-based
applications of value to the tactical user. Well-designed,
efficient networking protocols, can allow many more users
to share the limited avialable RF bandwidth. A significant
fraction of data traffic in the tactical environment may
consist of short datagram messages (e.g., position reports,
fire control, etc.). Also, relatively low data rate links
will also likely utilize relatively small packet MTU sizes.
As a result, any mechanisms which facilitate compression
of network headers are highly valuable in an IPng candidate.

<i>Configuration, Administration, and Operation.</i> The
tactical military has very real requirements for multimedia
services across its shared and interconnected 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 (QoS)
data delivery requirements are met for multimedia communication.

Note that this requires more than can be met by simple QoS-
based path selection and subsequent source-routing to get
realtime-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 CLNP specification were
not sufficient for our voice application with path selection.
Voice calls could not be routed adn resources reserved based
on any single QoS parameter (e.g., delay, capacity) 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 as a Type-of-Service
identifier to let the router know which datagrams were
associated with a voicecall. 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 as 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
correct interface {{why? broken design, this!}}, particularly
in cases where there were multiple communication media
interconnecting two routers along the path. Fortunately,
excluse use of the QoS indicator for voice in CSNI was able
to serve as a flag to the router for packets requiring
special handling.

<i>Flow specification.</i> 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 internetworking
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 capacity, an IPng could establish
a virtual circuit connection across this RF subnetwork which
meets the requirements of an RSVP Flow Specification. By creating
an assotiation between a particular Flow ID and the subnetwork
header identifying the established virtual circuit, and IPng
gateway could forward data across the low-capacity link while
removing most, if not all, of the IPng header information.
The receiving gateway could re-construct these fields based on
the Flow Specification of the particular Flow ID/virtual circuit

A field such as a Flow ID can serve at least two important

* 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).

* It can air mapping datagram services to different
types of communication services provided by special
subnet/data link layers protocols.

<i>Secure Operation.</i> As with any military system,
information security, including confidentiality and
authenticity of data, is of paramount importance. With
regard to IPng, network layer security mechanisms for
tactical RF networks are 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
communication systems or has tactical systems
interconnected 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 requirements for confidentiality and
authentication, an IPng candidate must be capable at
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

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 be dependant on a particular IPng protocol

<i>Multicast.</i> Tactical military communication has
a very clear requirement for multicast. Efficient
dissemiation of information to distributed war-fighting
participants can be the key to success in a battle.

In modren 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 network.

<i>Extensibility.</i> 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.) thre will be instances when there is not
sufficient capacity to provide all users with with
their perception of required communication capability.

It is extremely important for a shared, automated
communication system to to delegate capacity to higher
priority users. Unlike the commercial world, where
everyone has 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.

<i>Applicability.</i> There will be a significant
amount of applicability to tactical RF networks. The
current IP and CLNP are bing considerable attention
in the tactical RF community as a means to provide
communication interoperability across a large set of
heterogenous 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.

<i>Support for Mobility</i> 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 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 communications (SATCOM).

In some cases, 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 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. {{!!! why? broken protocol}}
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 aricraft strike force, or
Navy battlegroup.

<i>Datagram service.</i> 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 hte tactical communication environment.
The availability of platforms for routing and relaying is
never 100% certain in a tactical scenario. The efficiency
with which multicast can be implemented in a connectionless
network is highly critical in the tactical environment
where rapid, eficient information dissemination can be
a deciding factor. And, as it has been proven with several
different Internet applications and experiments, a
datagram service is capable of providing useful connection-
oriented and real-time connection services.

Consideration should be given in IPng to how it can co-exist
with other architectures usch 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, tec.) 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 supporti4g a similiar type of

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