One document matched: draft-ivancic-mobile-platforms-problem-00.txt
Ivancic W. Ivancic
Internet Draft NASA
Expires: March 2007 September 18, 2006
Multi-Domained, Multi-Homed Mobile Networks
draft-ivancic-mobile-platforms-problem-00.txt
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Abstract
This document describes numerous problems associated with deployment
of multi-homed mobile platforms consisting of multiple networks and
traversing large geographical areas. The purpose of this document is
to provide insight to real-world deployment issues and provide
information to working groups that are addressing many issues related
to multi-homing, policy-base routing, route optimization and mobile
security.
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Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in Error! Reference
source not found.RFC2119].
Table of Contents
1. Introduction...................................................2
2. Mobility solution space........................................4
2.1. Host-based Solutions......................................4
2.2. Radio-link layer mobility.................................5
2.3. Transport layer mobility..................................5
2.4. Routing Protocols for Mobile Networks.....................5
2.5. NEtworks in MOtion (NEMO).................................9
3. Policy-based routing..........................................10
4. Radio Operations..............................................13
4.1. Layer-2 Triggers.........................................13
4.2. Multiplexing Links.......................................14
4.2.1. Multiplexing at the Radio...........................14
4.2.2. Multiplexing at the Router..........................15
5. Network Access (auto-login)...................................16
5.1. Cellular Access..........................................16
5.2. Satellite Access.........................................17
5.3. WiFi Access..............................................17
6. Costs.........................................................17
7. Security Considerations.......................................18
8. IANA Considerations...........................................18
9. Acknowledgments...............................................18
10. References...................................................20
10.1. Normative References....................................20
10.2. Informative References..................................21
Author's Addresses...............................................21
Intellectual Property Statement..................................21
Disclaimer of Validity...........................................22
Copyright Statement..............................................22
Acknowledgment...................................................22
1. Introduction
The purpose of this document is to provide insight to real-world
deployment issues and provide information to working groups that are
addressing many issues related to multi-homing, policy-based routing,
route optimization and mobile security.
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This document describes numerous problems associated with deployment
of multi-homed, mobile platforms consisting of multiple networks in
multiple domains and traversing large geographical areas. These
multi-networked, multi-homed, multi-domained mobile networks are
often large platforms such as planes, trains, or ships and even
automobiles and spacecraft. One key characteristic that separates
them from general "networks in motion" (NEMOs) is that these
platforms have multiple networks that are generally owned and
operated by different parties (domains). Because of the various
network domains, policy-based routing and security have some
different issues and concerns relative to single-domained systems.
Three examples of multi-domained, multi-networked systems include:
defense systems, aeronautics systems and space systems. In all of
these systems there are critical control systems that reside in a
particular network that requires highly reliable links and time-
critical information, but limited bandwidth. We shall call this
network the "command and control" domain. A second network may be
present for operations and maintenance. This "operations and
maintenance" domain requires little bandwidth. In addition,
information is not as time-critical and reliability is relaxed. The
third network is the "user domain". This network generally requires
much more bandwidth than does command and control network or
operations and maintenance. However, this network, to date, is
generally not required to have data reach its destination within a
guaranteed time.
In the aeronautical industry, all critical air traffic control (ATC)
is performed via a closed network. Currently the air/ground link is
not Internet-based, but this is expected to change in the future.
All ATC traffic is time-critical and the links must be highly
reliable. However, these links require relatively little bandwidth
in the order of 10s of kilobits per second. This domain, to date,
has been a closed network with all infrastructure effectively owned
or controlled by the civil air authorities. In the United States of
America, this civil air authority is the Federal Aviation
Administration (FAA).
The second domain is the used for aircraft operations and maintenance
and is call the airline operational communications (AOC) network.
Information that may run on this network includes passenger lists,
aircraft fuel and weight and other operations and maintenance
information. This link is not as safety critical and the information
carried over this link is generally not time-critical. Like the ATC
domain, the AOC domain is closed although traditionally it has
resided within the same closed network as ATC.
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The third domain is the passenger domain. This domain is used for
in-flight entertainment (IFE) services and communication. To date,
the IFE network has not been allowed to carry any time critical ATC
communications. This policy is in place in part for security and in
part because the IFE network has not been specified and certified to
the same time-critical information transfer and reliability as the
ATC network. However that does not imply that the IFE network could
not meet those requirements.
A second example of multi-domained, multi-networked systems is the
deployment of Internet technologies for the United States National
Aeronautics and Space Administration (NASA) space program. Three
domains of interest for a spacecraft are: ground operations located
in Florida; mission control located in Texas; and the general science
community. Both ground operations and mission control require
reliable, time-critical commanding but do not require large amounts
of bandwidth - assuming video in sent on its own links. The user
network (scientific community) has greatly relaxed reliability
requirements and does not require time-critical information.
However, this network is expected to transport large volumes of data.
Each of these networks is effectively owned and operated by a
different community of interest on different domains.
Other multi-domained, multi-networked systems might be found in
military operations, the global shipping industry, taxi and limousine
services, and perhaps even in the general automotive industry.
2. Mobility solution space
Mobility here is the ability to move between radio systems and
networks without having to reestablish session. Mobility can be
performed as a host-based or network based solution. Mobility can
also be performed at various layers including the radio-link,
transport and network layers. Two network layer technologies are
applicable include routing protocols or mobile-ip based solutions
such as NEMO.
2.1. Host-based Solutions
Host-based solutions include: SCTP [RFC3286] at the transport layer,
HIP [RFC4423] as a shim between the network and transport layers and
mobile-ip at the network layer [RFC3344] [RFC3775]. A major problem
with host-based where a large number of hosts are sharing the same
low-rate radio link is that a binding update storm will occur when a
network is traversed. All hosts have to inform all of their
corresponding nodes as well as their location managers (e.g. home
agent for mobile-ip, DNS or some other location manager for SCTP, and
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rendezvous servers for HIP) when their location has changed. This
can saturate the RF link. Thus host-based solutions have a
scalability problem for this situation.
2.2. Radio-link layer mobility
Radio-link layer mobility is currently deployed in cellular systems
and work effectively over relatively large geographical areas (i.e.
countries and continents). Use of radio-link handoffs for mobility
provides a partial solution over a limited space. Radio-link layer
handoffs only solve mobility problems for a single link. It does
not address multihoming nor is it scalable over extremely large
geographic areas (i.e. globally). Since multiple providers, possibly
with multiple access link technologies, are usually required for
global connectivity, link-layer mobility solutions alone are not
feasible for global mobility.
2.3. Transport layer mobility
Transport layer mobility using Stream Control Transport Protocol
(SCTP) provides route optimization and potentially could provide good
convergence times. As with any non-routing protocol, transport layer
mobility requires some sort of location manager to enable a
corresponding node to initiate communications. The location manager
is used by the mobile node to register its current location. Use of
Domain Name Servers (DNS) has been shown to functionally perform this
function using "do not cache" options. However, the reliability and
convergence time for updating the DNS has not been proven
operationally as often times the "do not cache" option is ignored
[Pan2004].
SCTP-based transport layer mobility and has been implemented as a
host-based solution. This solution currently is not applicable for
large mobile networks. However, research is being performed to use
one-to-one address translation to provide network-based SCTP whereby
one host acts and an SCTP proxy for all hosts behind it performing
SCTP for all hosts behind it. Conceptually this effectively performs
transport-layer mobile routing. However, even if SCTP can be adapted
to handle many nodes, binding update storms may still be a problem.
2.4. Routing Protocols for Mobile Networks
Routing protocols provide route optimization as that is their job.
There are a number of problems with using routing protocols to solve
the multi-domained, multi-homed mobile network problem including:
convergence time, inability to share network infrastructure,
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addressing, scalability and the applicability of some routing
protocols for particular applications.
Figures 1 and 2 illustrate some of the major issues with using
routing protocols for mobile networks. Figure 1 shows how the
current International Organization for Standardization (ISO)
standards based Aeronautical Telecommunication Network (ATN) as
specified by the International Civil Aviation Organization (ICAO).
Figure 2 shows a conceptual migration to use of internet protocols
(IP) to perform the same function.
O---------O O---------O
|Mobile RD| |Mobile RD|
O------+--O O----+----O
\ /
.--+--------------------------+-------.
| `--+ ATN Backbone / |
| +-+-.------------------+----+ |
| | ,-`---. ,--+--. | |
| | (ATN TRD)-------(ATN TRD) | |
| | `---+-' `---+-' | |
O---------O | +-----+----------------:----+ |
|Mobile RD|-+. / \ |
O---------O | `-. ,-+---. \ |
| `-ATN TRD--. .----+--. |
| `--+--' `--------|ATN ERD| |
| ; `-------' |
| / |
| / |
| .---+---. |
| |ATN ER | ATN Island RDC |
| `-------' |
`-------------------------------------'
ERD - End Routing Domain
RD - Routing Domain
RDC - Routing Domain Confederation
TRD - Transit Routing Domain
Figure 1 Aeronautical Telecommunication Network Island
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Air | Ground
|
|
| +--------+
| )-|BGP/OSPF|\
+----+ | +--------+ `. .------.
|BPG |-( | \| OSPF |
+----+ | /|AREA 1|`.
Mobile-1 | +--------+ .' `------' `.
| )-|BGP/OSPF|/ `.
| +--------+ .------.
+----+ | | OSPF |
|BPG |-( | |AREA 0|
+----+ | +--------+ `------'
Mobile-2 | )-|BGP/OSPF|`. .'
| +--------+ \ .------. /
| `.| OSPF | .'
| .'|AREA N|'
+----+ | +--------+ / `------'
|BPG |-( | )-|BGP/OSPF|.'
+----+ | +--------+
Mobile-N |
|
Figure 2 Internet Protocol Based Aeronautical Network
For mobile networks that require time-critical command and control,
fast convergence time is essential. Take, for example, the ATC
problem with aircraft takeoff and landing. This is the most crucial
portion of a flight. One cannot wait 30 to 90 seconds or a few
minutes for routes to converge. The same is true for a spacecraft
during launch when it is passing numerous ground stations in a short
time. In order to control the convergence time in aeronautical
networks, the ISO Inter Domain Routing Protocol (IDRP) is used
[ISO10747]. To further improve convergence time, the network is
constructed as a highly controlled two tier architecture consisting
of transit routing domains and backbone interconnectivity. The
concept is that route propagation will occur quickly in the transit-
domain where information is time-critical [Sig1998]. Route
propagation to geographically distant areas will occur over the
backbone where route propagation is not time-critical [Figure 1].
In the IP implementation of figure 2, BPG-4 [RFC4271] is seen as an
external route to the OSPF network [RFC2328]. Since the aeronautics
network is relatively small and currently a closed network operated
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jointly by various civil aviation authorities, OSPF can be used
globally. When a BGP route is advertised to the OSPF network, the
OSPF network will immediately propagate the route into the nearest
OSPF area thereby provide good convergence time locally where it
matters most [Iva2006].
In figures 1 and 2, IDRP and BGP are also used to provide policy-
based routing capability. This is of interest and a current
requirement for the aeronautics community in order to have time-
critical command and control flow through one link while other
traffic such as air operations flows through another. Although this
requirement has existed within the ICOA ATN specification from the
beginning [ICAO9739] [ICAO9705], its use has seen limited deployment
to date and is operationally untested for the following reasons:
there currently are not enough ATN users to tax the system; system
deployment is minimal; and, the airlines generally only have one link
active for cost reasons. For example, satellite links are not turned
on unless needed due to the high cost. Furthermore, two simultaneous
VHF radios are not active simultaneously.
When using BGP or other routing protocols for mobility, additional
problems arise due to addressing. Routing protocols generally
assume the interface connections on the routers are not dynamically
changing. Thus, two routes connected are assumed to be on the same
subnet. One may be able to use "un-numbered" serial interfaces to
alleviate this problem, but to date, this has not been proven to
work. Thus, all mobile platforms must reside in the same network or
sub-network. It may be possible to achieve this by having the mobile
platform obtain its WAN interface address from the ground using PPP,
DHCP, or IPv6 auto configuration.
Regarding use of an inter-autonomous system protocol such as BGP,
scalability issues arise due to the need to configure peering. Each
BGP router has to have a configuration for each autonomous system
(AS) peer that wishes to communicate with. Thus, each mobile has to
have preconfigured for each radio station router it will communicate
with. Likewise, each radio station router will have to be
preconfigured for each mobile. As the number of ground stations or
mobile platforms grows, this quickly becomes unmanageable. As new
mobile platforms or ground stations are added, all configurations
must be updated. Furthermore, if the mobile platforms have multiple-
domains, the question of who is authorized to update systems becomes
an issue.
Using general routing protocols for mobility make it very difficult
to share infrastructure. In order to run routing protocols, one
generally has to either own all of the assets or pre-arrange peering
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agreements. For security reasons, one cannot simple inject routes
into another's network. Furthermore, allowing relatively small
mobile networks to inject routes that do not conform to some form of
route aggregation will result in route table explosion and is
therefore not scalable or desirable
2.5. NEtworks in MOtion (NEMO)
Networks in Motion (NEMO) protocols have been designed specifically
to manage the mobility of an entire network (or networks), which
changes, as a unit, its point of attachment to the Internet and thus
its reachability in the topology [RFC3963]. NEMO protocols also
address multihomed networks which may be either a single mobile
router (MR) that has multiple attachments to the internet, or may use
multiple MRs that attach the mobile network to the Internet.
NEMO protocols, by design, avoid many of the problems associated with
using general routing protocols for mobile networks including:
convergence time, the need for two communicating routers to reside on
the same subnet and the need to pre-configure peering relationships.
Mobile-ip based solutions such as NEMO solutions have relatively fast
convergence times as mobile-ip based protocols simply redirecting the
default-route pointer. However, if one wishes to pass routing
protocols down a mobile-ip tunnel, then convergence issues may still
exists.
NEMO solutions also allow one to easily share. NEMO solutions do not
require the mobile to inject routes into another's network. Rather,
for each radio link one simply contracts with an Internet Service
Provider (ISP) for bandwidth and access. The ISP provides a care-of-
address once radio-link access is granted. The user can use the
bandwidth however they wish. (Note, this model may change if mobile
network users dominate use of the IPS's network. At that point, the
cost model may change whereby a mobile network user pays an
appropriate usage fee relative to the capacity used.)
Two areas that NEMO protocols have yet to mature in are support for
route optimization and policy-based routing.
Current NEMO support requires a bi-directional tunnel between the
mobile router and the home agent. This can result in significant
delays when the mobile unit traverses large distances. These
distances can be global distances (or beyond for space systems). It
is highly desirable to have route optimization at least to the point
of being able to bind a mobile node to a geographically closer home
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agent. Route optimization is expected to be the next area of work
being performed by the NEMO working group.
Another area of route optimization relative to mobile-ip and NEMO is
network-based local mobility management (netlmm). Local
mobility involves movements across some administratively and
geographically contiguous set of subnets. When a mobile node
moves from one access router to another, the access routers send a
route update to the mobility anchor point. While some mobile node
involvement is necessary and expected for generic mobility functions
such as movement detection and to inform the access router about
mobile node movement, no specific mobile node to network protocol
will be required for localized mobility management itself. Netlmm
technology may prove useful for common radio systems owned and
operated by a single entity. In the aeronautics community, netlmm
may be useful for connecting all of the VHF radios in a given control
area. For a space mission, netlmm between tracking ground stations
may greatly improve performance for time critical commanding.
Past implementations of NEMO IPv4 or IPv6 protocols only allow for
binding to one care-of-address. In this situation, a multihomed
mobile router can only use one link at a time. It is not capable of
using two or more links even if they are available. Use of multiple
links simultaneously is desirable for a number of reasons including
load balancing and policy-base routing. The problem of policy-base
routing is currently being investigated by Mobile Nodes and Multiple
Interfaces in IPv6 (monami6) working group. Two topics being
investigated that of interest to multi-domained, multi-homed mobile
networks are:
. A protocol extension to Mobile IPv6 (RFC 3775) and NEMO Basic
Support (RFC 3963) to support the registration of multiple Care-of-
Addresses at a given Home Agent address [Wak2006].
. A "Flow/binding policies exchange" solution for an exchange of
policies from the mobile host/router to the Home Agent and from the
Home Agent to the mobile host/router influencing the choice of the
Care-of Address and Home Agent address [Sol2006].
3. Policy-based routing
Figures 3 through 6 illustrate the advantages of policy-based routing
in a mobile aeronautical network. Consider the mobile network having
three links available. One link is classified as highly reliable but
relatively low rate. This link is reserved for command and control.
The second link is a low-latency, low-bandwidth link. The third link
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is high-rate for passenger services. Assume it is possible to set
policy with the following rules:
. Only ATC traffic is allowed to use the reliable link.
. Data precedence is set such that ATC is highest priority, AOC is
next highest and passenger traffic has lowest priority.
. ATC and AOC traffic are allowed to use the low-latency link
. ATC, AOC and passenger traffic are allowed to use the high-rate
link.
. Link preference for ATC is reliable link - highest, low-latency
link - middle, high-rate - last.
. Link preference for AOC is low-latency followed by high-rate.
Figure 3 shows all links active. Figure 4 shows that ATC traffic
can be delivered even if all other links are unavailable. Figure 5
shows that ATC and AOC traffic have precedence over passenger traffic
and could use the high-rate link if their preferred links are
unavailable. Figure 5 is of greatest interest because one could
conceivably make this the preferred link for all traffic if safety-
of-flight QoS requirements could be met. Doing so would release
spectrum to ATC and AOC as many users could be using the high-rate
links when available. (For aeronautical communications, RF spectrum
is a precious and limited resource.) |
|
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+-+-+ +-+-+
|P-3| |P-3|
+-+-+ +-+-+
| |
+-+-+ High-Speed Link | +-+-+
|P-2| +---+ +---+ | |P-1
+-+-+ |P-3|============|P-3|=+ +-+-+
| +---+ +---+ | |
+-+-+ / | +-+-+
|P-1| / Low Latency Link | .-- --. |P-2
+-+-+ .--+---. +---+ | |Home | +-+-+
+-------|Router|========|P-2|========+-|Agent|-----+
+-+-+ `--.---' +---+ | `-- --' +-+-+
|P-3| `. | |P-3
+-+-+ `. +---+ | +-+-+
| `=|P-1|==============+ |
+---+ |
Reliable Link |
Figure 3 Policy-Based Routing, All Links Active
| |
+-+-+ |
|P-3| |
+-+-+ |
| |
+-+-+ High-Speed Link |
|P-2| +---+ \ / | |
+-+-+ |P-3|==============+===+ |
| +---+ / \ | |
+-+-+ / | +-+-+
|P-1| / Low Latency Link | .-----. |P-1|
+-+-+ .--+---. +---+ \ / | |Home | +-+-+
+-------|Router|========|P-2|====+===+-|Agent|-----+
+-+-+ `--.---' +---+ / \ | `-----' |
|P-3| `. | |
+-+-+ `. +---+ | |
| `=|P-1|==============| |
+---+ |
Reliable Link
Figure 4 Policy-Based Routing, Critical Link Active
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| |
+-+-+ +-+-+
|P-3| |P-3|
+-+-+ +-+-+
| | |
+-+-+ High-Speed Link | +-+-+
|P-2| +---+ +---+ +---+ +---+ | |P-3|
+-+-+ |P-3|=|P-3|==|P-2|=|P-1|=+ +-+-+
| +---+ +---+ +---+ +---+ | |
+-+-+ / | +-+-+
|P-1| / Low Latency Link | .-----. |P-2|
+-+-+ .--+---. \ / | |Home | +-+-+
+-------|Router|===========+===========+-|Agent|-----+
+-+-+ `--.---' / \ | `-----' +-+-+
|P-3| `. | |P-1|
+-+-+ `. \ / | +-+-+
| `=================+====+ |
/ \ |
Reliable Link |
Figure 5 Policy-Based Routing, User Link Active
4. Radio Operations
Mobile networks are wireless and may utilize many types of radio
systems. It is imperative to understand the interaction between
particular radio systems and the routing and transport protocols.
For example, the Transmission Control Protocol (TCP) has algorithms
to enable it to probe the network for capacity and adjust
accordingly. Streaming video or rate-based protocols do not and can
easily saturate a link if not properly controlled. Two techniques
that can be used to control non-congestion-friendly protocols are
policy-base routing and queue management.
4.1. Layer-2 Triggers
For low rate (10s of kbps) radio links such as current avionics links
some minimal quality-of-service can be accomplished via message
prioritization. When link capacity is low there is little need to
have a feedback mechanism between the radio and the router to enhance
QoS. Current and future high-rate links would benefit greatly by
having a standardized feedback mechanism between the radio systems
and the router. Such mechanism could indicate if a link is
available and the quality and bandwidth of the link. The former is
important for fast handovers between links. The latter is of
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particular importance for bandwidth-on-demand systems. For
instance, the Boeing Connexion outbound radio link can operate from
approximately 16 kbps up to 1 or 2 Mbps in 16 kbps increments. This
rate is continually varying depending on outbound traffic demands and
satellite network congestion. Assuming the interface between the
router and Connexion radio is an Ethernet connection, some type of
layer-2 trigger or feedback to the router is necessary to determine
the available data rate. If the interface is serial, having the
radio provide the clock may solve the data rate problem.
4.2. Multiplexing Links
When building a robust mobile communication system, it is highly
desirable to have multiple radio types to ensure communication (e.g.
cellular, WiFi, satellite). Each of these radio link technologies
operates at different frequencies and has different antenna
technologies that must be incorporated into the system design. Radio
systems and their associated antenna systems can add significant
size, mass and power to communication systems. Thus, although it is
highly desirable to have multiple radio systems, there is a practical
limit to what can be deployed. One most certainly does not want to
have to deploy multiple radios of the same technology. Rather one
will multiplex communications over similar radios.
4.2.1. Multiplexing at the Radio
Figure 6 illustrates multiplexing communications at the radio link.
For each link, all information must be queued and prioritized in the
"MUX" box. This is not overly difficult.
One of the main problems with multiplexing at the radios is that the
MUX box must obtain or be configured for addressing on the various
wireless networks. The MUX box must pass this addressing on to the
NEMO routers. For example, the MUX on the WiFi network may obtain
its Wide Area Network (WAN) address via DHCP. The MUX must now
provide addressing to the various NEMO routers attached to the
ingress side. Does the WiFi MUX provide different addresses to each
NEMO router or the same address? How is this done? One would like
this to be a standardized method.
One advantage that the architecture in figure 6 provides is physical
separation of the NEMOs. Thus, security issues for this architecture
may be accomplished using a conventional approach. However, if each
NEMO is getting the same WAN address, this is certainly not
conventional.
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+--------+
+---------+..........,-----. ,----------.-'''"""| NEMO-1 |
| NEMO-1 |. .( MUX )---| Satellite|\ /| HA |
+---------+ \ / `-----' '----------* \ / +--------+
\ `. .' / | \ /,'
\ `. / `. X |
\' `. `/ ,'
/ \ / \ /|,'\
+---------+' \| `,-----. ,----------./ `| \+--------+
| NEMO-2 |-----+---( MUX )---| WiFi |..,:...| NEMO-2 |
+---------+. /\ .'`-----' '----------*\,'`. | HA |
\ / \/ ,' | /+--------+
`. .'\ | \ ;;
/ X \ ,' X `.
/ .' `. \ ' ," \ |
+---------+ / \ ,-----. ,----------./ \`+--------+
| NEMO-3 |' `( MUX )---| VHF | \| NEMO-3 |
+---------+--------- `-----' '----------*-......| HA |
+--------+
Figure 6 Multiplexing at the Radio
4.2.2. Multiplexing at the Router
Figure 7 illustrates combining information in the router rather than
a special MUX box per figure 6. Here, multiple NEMOs are configured
in a single router. There are many advantages to this architecture
over the one in figure 6. First, there is no need for MUX boxes.
Second, only one router interface is necessary for each radio system;
therefore, traditional forms of acquiring a WAN address can be
used(i.e. DHCP, PPP, Auto-configuration, manual configuration) and
the same address is not assigned to multiple interfaces. Third, only
one router is required for multiple NEMOs versus use of multiple
NEMOs, one for each domain. Thus, there is potential for mass,
power, volume and cost savings. Furthermore, this architecture is
potentially much easier to manage.
A definite security concern with multiplexing NEMOs and radios at the
router is that various domains may be cross connected if
configurations are not tightly controlled.
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_____+--------+
,----------.--------------| NEMO-1 |
| Satellite|`. ,"| HA |
," '----------*\ `. ," /+--------+
,-" \ `. ," /
+----------+ ," \ ;; /
| |,-" `," `./
| NEMO-1 | ," \ /`.
| | ,----------.," \ / `.+--------+
| NEMO-2 |-----------| WiFi |......,;......| NEMO-2 |
| | '----------*`. / \ | HA |
| NEMO-3 |`. `./ \ ,"+--------+
| | `. /`. ,-;
+----------+ \ / `," \
`. / ," `. \
`. ,----------. ,-" `. +--------+
`.| VHF |," `.| NEMO-3 |
'----------*............. | HA |
`+--------+
Figure 7 Multiplexing at the Router
5. Network Access (auto-login)
Obtaining access to a wireless network may be non-trivial for a
mobile platform, depending on the wireless technology being deployed.
A mobile platform SHOULD be able to obtain network access in an
automated manner.
5.1. Cellular Access
For cellular systems, access is usually accomplished via prearranged
security and access agreements. A user contracts for bandwidth with
a service provider and obtains a cellular modem that has a
corresponding electronic serial number. When the modem (phone) makes
a call, it transmits the ESN and the Mobile Identification Number
(MIN)- also referred to as MSID (Mobile Station Identification)- to
the network at the beginning of the call. The MIN/ESN pair is a
unique tag for each modem and is used to establish the system's
credentials and allow access to the wireless network. PPP or some
other protocol can then be used to obtain a care-of-address.
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5.2. Satellite Access
Satellite radio network access may be performed in a similar manner
to cellular radio systems depending on the provider. In some
satellite modems a form of electronic serial number or media access
control (MAC) address is associated with a modem. Once the ESN (or
MAC) is validated, the user obtains access to the network. Network
addresses are obtained using PPP or statically configured addresses.
5.3. WiFi Access
WiFi radio access is somewhat different than cellular or satellite
access. Three basic modes of wireless network access are used: open
network, preconfigured and negotiated.
For open networks, any radio simply scans for a radio network and
obtains access. Layer-3 address is usually provided via DHCP. Such
radio and layer-3 access works well for a machine access (i.e. mobile
router access).
A preconfigured access will work for machine-to-machine operations.
Such pre-configurations are usually found on private networks. Here,
a pre-placed key may be used along with a security protocol such as
Wired Equivalent Privacy (WEP) (802.11 encryption protocol). Media
Access Control physical addresses may also be configured into access
list to limit what radios are allowed to connect to the network.
As security and accountability concerns grow, radio network access is
moving toward negotiated access. Here, a user/name and password or
some type of token ID and password are required for access. Such
secure radio network access techniques include Extensible
Authentication Protocol (EAP), and WiFi Protected Access (WPA).
Currently such systems focus on the needs of the human mobile user
who is in need of short term network access. Machine-to-machine
negotiation of radio network access is not part of this operational
scenario. Such concepts are new and businesses cases have yet to be
considered. For NEMOs to take advantage of WiFi networks, techniques
that allow for machine-to-machine radio access without the need for
human intervention are imperative.
6. Costs
Although not a protocol issue, the ISP cost model plays a significant
role in the ability to deploy large mobile networks especially if
they are multi-domained, multi-homed mobile networks. Fixed rate
network access is essential to make it viable to budget for a mobile
network. Paying a fixed price for a fixed amount of bandwidth works
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well as end users can budget for this cost model. If one has to pay
by the amount of data that transitions a given network or connect
time, it becomes extremely difficult to budget operations. For
large-capacity users as it is extremely difficult to project how much
data one will transfer over the link from one month to the next.
Likewise, if one is being charged for connect time, one needs to
deploy a mechanism that only brings a link up when it is needed.
This results in a system that is out-bound oriented. Peer-to-peer
communications only occurs when the links are turned on. Thus, in
order for a corresponding node to initiate communications with the
mobile node, some sort of back-channel has to be used to the mobile
node to turn on the link of interest.
7. Security Considerations
Having a single router operating in multiple domains either via
generic routing protocols or use of mobile-ip based NEMO protocols
has serious security issues. The possibility of having a single
mobile router connected to multiple home agents residing in various
domains implies that these domains could be inadvertently connected
if the mobile router is misconfigured. Similarly, unless great care
is taken to configure mobile platform routers that use generic
routing, cross-domain connectivity can easily occur.
Management of multi-domain routers is an interesting policy problem.
"Who has authority to configure and control the mobile unit?
ISPs often implement security mechanisms that break NEMO and mobile-
ip. One example of this is deployment of administrative filtering.
Here, an ISP may decide to have an out-bound only policy such that
all traffic must have originated from within their network. At least
one GPRS ISP has such a policy in place. One explanation provided
for such a policy is to keep potentially hostile Internet traffic off
the network. Probing the GPRS system address space not only posses a
threat to customers, but, more importantly steals precious GPRS
bandwidth from the users [Iva2003].
8. IANA Considerations
There are no IANA considerations as this is an informational
document.
9. Acknowledgments
The author would like to thank Terry Bell, Wesley Eddy, David Stewart
and Terry Davis for their review and comments. The author would like
to thank Joe Touch for his Microsoft Word template [Tou2006]. The
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author would particularly like to thank Markus Gebhard - a picture is
worth a thousand words.
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10. References
10.1. Normative References
[ICAO9705]"Manual of Technical Provisions for Aeronautical
Telecommunication Network (ATN) - 3rd Edition", June 2002
[ICAO9739]"Comprehensive Aeronautical Telecommunication Network
(ATN)", September 2000
[ISO10747]ISO/IEC 10747:1994, Protocol for Exchange of Inter-Domain
Routing Information among Intermediate Systems to Support
Forwarding of ISO/IEC 8473 PDUS.
Error! Reference source not found.RFC2119] Bradner, S., "Key words
for use in RFCs to Indicate Requirement Levels", BCP 14,
RFC 2119, March 1997.
[RFC2328] Moy., J., "OSPF Version 2", RFC 2328. April 1998
[RFC3286] Ong, L., Yoakum, J., "An Introduction to the Stream Control
Transmission Protocol (SCTP)", RFC 3286, May 2002.
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
[RFC3775] Johnson, D., Perkins, C., Arkko, J., "Mobility Support in
IPv6", RFC 3344 June 2004.
[RFC4271] Rekhter, Y., Li, T., Hares, S., "A Border Gateway Protocol
4 (BGP-4)", RFC 4271, January 2006.
[RFC4423] Moskowitz, R., Nikander, P., "Host Identity Protocol (HIP)
Architecture", RFC 4423, May 2006.
[Sol2006] Soliman, H., Montavont, N., Fikouras, N., Kuladinithi, K.,
"Flow Bindings in Mobile IPv6", draft-soliman-monami6-flow-
binding-01.txt, work in progress, expires December 2006
[Wak2006] Wakikawa, R., Nagami, K., "Multiple Care-of Addresses
Registration", draft-ietf-monami6-multiplecoa-00.txt, work
in progress, expires December 2006
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Internet-Draft Multi-Domained Multi-Homed Mobile Networks September 2006
10.2. Informative References
[Iva2003] Ivancic, W., "Administrative Filtering", September 2003,
http://roland.grc.nasa.gov/~ivancic/papers_presentations/20
03/administrative_filtering.pdf
[Iva2006] Ivancic, W., "Aircraft Mobility using a combination of
Internet Standards", ICAO Aeronautical Communications
Panel(Acp)Working Group N - Networking Subgroup N1 -
Internet Communications Services ACP/WG N/SG N1 Paper 801,
May 2006,
http://roland.grc.nasa.gov/~ivancic/papers_presentations/20
06/ICAO_WG-N_SG-N1_WP-801.pdf
[Pan2004] Pang, J., Akella, A., Shaikh, A., Krishnamurthy, B.,
Seshan, S.,"On the Responsiveness of DNS-based Network
Control",Proceedings of the Internet Measurement Conference
2004, October 2004.
[Sig1998] Signore, T., Girard, M., "The Aeronautical
Telecommunication Network (ATN)", IEEE 0-7803-4902-4/98/,
1998
[Tou2006] Touch, J., "Version 2.0 Microsoft Word Template for
Creating Internet Drafts and RFCs", draft-touch-msword-
template-v2.0-04.txt, work in progress expires August 2006
Author's Addresses
William D. Ivancic
NASA Glenn Research Center
21000 Brookpark Road MS 54-5
Cleveland, OH 44135
Phone: +1 (216) 433-3494
Email: William.D.Ivancic@nasa.gov
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