MANET Autoconfiguration (AUTOCONF) I. Chakeres
Internet-Draft Motorola
Intended status: Informational J. Macker
Expires: April 5, 2008 Naval Research Laboratory
T. Clausen
LIX, Ecole Polytechnique
October 3, 2007
Mobile Ad hoc Network Architecture
draft-ietf-autoconf-manetarch-06
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 5, 2008.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document discusses Mobile Ad hoc NETworks (MANETs). It presents
the initial motivation for MANET and describes unaccustomed
characteristics and challenges. It also defines a MANET, other MANET
entities, and MANET architectural concepts.
Chakeres, et al. Expires April 5, 2008 [Page 1]
Internet-Draft MANET Architecture October 2007
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Borrowed Terminology . . . . . . . . . . . . . . . . . . . 3
2.2. MANET Terminology . . . . . . . . . . . . . . . . . . . . 4
3. MANET Motivation Discussion . . . . . . . . . . . . . . . . . 6
3.1. Packet Radio Networks . . . . . . . . . . . . . . . . . . 6
3.2. Packet Radio Networks and the Internet . . . . . . . . . . 6
3.3. Packet Radio Networks and MANETs . . . . . . . . . . . . . 7
4. MANET Interface Characteristics . . . . . . . . . . . . . . . 8
4.1. Qualities - Wireless, Mobile, Ad hoc . . . . . . . . . . . 8
4.2. Challenges . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Semi-Broadcast Interface . . . . . . . . . . . . . . . 8
4.2.2. Fuzzy Relationships Between Nearby MANET Routers &
MANET Routers' Extended Neighborhoods . . . . . . . . 9
4.2.3. MANET Membership . . . . . . . . . . . . . . . . . . . 10
5. Addressing & the MANET Prefix Model . . . . . . . . . . . . . 11
5.1. General Address Architecture . . . . . . . . . . . . . . . 12
5.2. MANET Interface Configuration . . . . . . . . . . . . . . 13
5.3. Routers and Hosts in a MANET . . . . . . . . . . . . . . . 13
6. MANETs' Place in the Network Stack . . . . . . . . . . . . . . 14
7. Sharing of Information Across Layers . . . . . . . . . . . . . 15
8. Deployment Taxonomy . . . . . . . . . . . . . . . . . . . . . 15
8.1. Service Availability . . . . . . . . . . . . . . . . . . . 15
8.2. Number of MANET Routers in a MANET . . . . . . . . . . . . 16
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
12. Informative References . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . . . . 20
Chakeres, et al. Expires April 5, 2008 [Page 2]
Internet-Draft MANET Architecture October 2007
1. Introduction
A Mobile Ad hoc NETwork (MANET) consists of a loosely connected
domain of routers. A MANET is characterized by inclusion of one or
more MANET interfaces; interfaces that are distinguished by their
potentially significant time-vary asymmetric reachability amongst
neighboring routers. These routers organize and maintain a routing
structure among themselves. These routers may communicate over
dynamic wireless channels with asymmetric reachability, may be
mobile, and may join and leave the network at any time. These
MANETs' characteristics create challenges in several areas.
This document is focused on IP networking, though many of MANETs'
concepts and issues span the protocol stack.
This document is meant to complement [RFC2501] in describing and
defining MANET.
2. Terminology
Owing to the fact that a MANET, as described in this document, is an
instance of an IP network, much of the terminology employed in this
document is borrowed from existing documents. Some of the documents
that contain relevant terminology are [RFC1812], [RFC2328],
[RFC2453], [RFC2460], [RFC2461], [RFC4291], [RFC3753], and [RFC4903].
In some cases the terminology is slightly abbreviated or rephrased;
although, every effort made to retain the meanings. Borrowed
terminology is provided in Section 2.1 with the intent of providing a
complete discussion of MANETs using coherent terminology. MANET
specific terminology is provided in Section 2.2.
2.1. Borrowed Terminology
This document employs the following definitions:
Node (N)
any device (router or host) that implements IP.
Router (R)
a node that forwards IP packets not explicitly addressed to
itself.
Host (H)
any node that is not a router, i.e. a host does not forward
packets addressed to others.
Chakeres, et al. Expires April 5, 2008 [Page 3]
Internet-Draft MANET Architecture October 2007
Link
a communication facility or medium over which nodes can
communicate at the link layer, i.e., the layer immediately below
IP. Examples are Ethernets (simple or bridged), PPP links, X.25,
Frame Relay, or ATM networks as well as internet (or higher) layer
"tunnels", such as tunnels over IPv4 or IPv6 itself.
Asymmetric Reachability
Asymmetric reachability describes two properties of certain
interface types' underlying communication facilities. First, non-
transitive communication means packets from X can reach Y, and
packets from Y can reach Z, but packets from X may not reach Z.
Second, non-bidirectional communication means that packets from X
can reach Y but packets from Y may not reach X. Many radio/
wireless interfaces exhibit these properties.
Neighbor
In the context of routing, two routers are neighbors if one can
send/receive routing protocol IP packets to the other without
passing through any intermediaries at the same layer.
Interface
A node's point of attachment to a communication link.
Semi-Broadcast Interface (SBI)
A broadcast capable interface that may exhibit asymmetric
reachability. Multiple access wireless radio interfaces are often
SBI. Note that since a SBI *may* exhibit asymmetric reachability,
it also may not.
Routing Domain (Domain)
A routing domain is an interconnected network with a coherent
routing policy and a consistent metric framework.
Border Router (BR)
A border router participates in multiple routing domains, and
often multiple routing protocols. A BR defines the border between
its multiple routing domains. A BR is responsible for presenting
a consistent picture of the nodes reachable through itself to each
routing domain. A BR determines the routing information to
propagate between different routing domains.
2.2. MANET Terminology
The following terminology is specific to MANETs:
Chakeres, et al. Expires April 5, 2008 [Page 4]
Internet-Draft MANET Architecture October 2007
MANET Interface
A MANET interface is distinguished by its potentially significant
time-varying asymmetric reachability (e.g., SBI) amongst potential
neighboring routers. A more detailed discussion of MANET
interface characteristics is presented in Section 4.2. The
addressing constraints for a MANET interface are discussed in
Section 5.2.
MANET Router (MNR)
A MANET router is distinguished by having one or more MANET
interfaces. A MANET router may also have zero or more non-MANET
interfaces. A MANET router is responsible for hiding MANETs'
challenging characteristics from nodes that are not MANET-aware.
A MANET router with a single MANET interface is illustrated in
Figure 1.
MANET Neighborhood
a set of neighboring routers that can communicate via MANET
interfaces without passing through any other routers
(intermediaries at the same layer).
MANET
a routing domain containing MANET routers. A example MANET is
illustrated in Figure 3.
<~~~~~~+~~~~~~> MANET
| Interface
'''''''''''''
' MANET '
' Router '
'''''''''''''
Figure 1: MANET Router with One MANET Interface
Dependent upon the deployment and management strategy, coalescing and
fragmentation of MANETs may be a supported feature. In other words,
if a communication path between two previously separated MANET
routers or MANETs becomes available, the two MANETs may merge to form
a single larger MANET. Similarly, if a communication path between
two MANET routers disappears and no alternative path between the
routers exists, then the MANET may be partitioned into two separate
MANETs.
When discussing MANETs' connectivity to other networks, such as the
Internet, a MANET is bounded by border routers (BR). That is, a
MANET's BR form a border between a MANET and other routing domains.
Chakeres, et al. Expires April 5, 2008 [Page 5]
Internet-Draft MANET Architecture October 2007
3. MANET Motivation Discussion
The Internet Protocol (IP) core design tenets -- connectionless
networking and packet-based forwarding -- are ideally suited for use
in highly dynamic contexts, such as MANETs. Yet, some additional
functionality is required to meet the unique challenges and
opportunities present in MANETs.
3.1. Packet Radio Networks
The initial motivation for MANETs was called Packet Radio (PR)
networking [FL01]. In PR, each router is equipped with a single
wireless interface. Each router may be mobile, and the routers may
be or may become spatially distributed such that all routers cannot
communicate directly. That is, two routers might require one or more
intermediate routers to forward (route) packets on their behalf. In
the example shown in Figure 2: for PR1 to send packets to PR3, the
intermediary PR2 must relay the packets. This implies that PR2 must
receive the packet from PR1 on its interface and determine that it
must retransmit the packet over the same interface as the one where
the packet was received, in order for the packet to reach PR3. From
the point of view of PR2, both PR1 and PR3 are neighboring routers,
whereas PR1 and PR3 are not themselves neighboring routers of one
another.
Communication
Range
<~~~~~~+~~~~~~> <~~~~~~+~~~~~~>
Single | <~~~~~~+~~~~~~> |
MANET +-|-+ +-|-+ +-|-+
Interface |PR1| |PR2| |PR3|
+---+ +---+ +---+
Figure 2: Basic Packet Radio Network
3.2. Packet Radio Networks and the Internet
Packet Radio networks inspired several architecture related
challenges, including how to interconnect Packet Radio networks and
other networks, especially fixed networks like the ARPANET. Another
related challenge was how to deal with the large disparity between
different node and interface characteristics present in different
networks.
These aspects of Packet Radio networks helped stimulate the early
development of the Internet Protocol; an architecture based on
Chakeres, et al. Expires April 5, 2008 [Page 6]
Internet-Draft MANET Architecture October 2007
connectionless networking and packet-based forwarding that enables
interconnection of heterogeneous devices over heterogeneous
communication technologies.
3.3. Packet Radio Networks and MANETs
The router configuration in Figure 1 is the simplest MANET router
configuration: a single interface exhibiting MANET interface
characteristics. Many other challenges exist, in MANETs and in
Packet Radio Networks both: wireless interfaces imply shared
communication resources which result in interdependence between
nearby nodes, and these nodes often communicate directly or
indirectly. Wireless channel statistical dynamics and node mobility
may result in frequent packet channel losses and network topology
changes.
Figure 3 shows a general schematic of a MANET: each MANET Router
(MNR) has one or more MANET interfaces, over which MANET interface
aware protocols operate to ensure MANET communication; and zero or
more non-MANET participating interfaces, either towards hosts or
other networks. Over these non-MANET aware interfaces protocols need
not be aware of MANETs' characteristics.
+---+
|MNR|
+-|-+
+-+ +---+ / /|\ \ +---+ +-+
| |...MNR--- .-. ---MNR|..| |
+-+ +---+ \ ,-( _)-. / +---+ +-+
.-(_ MANET )-.
Other ( Communication )
Nodes `-(______)-'
and \|/ \|/
Networks +-|-+ +-|-+
|MNR| \|/ |MNR|
+-:-+ +-|-+ +-:-+
: |MNR| :
+-+ +-:-+ +-+
+-+ : +-+
+-+
+-+
Figure 3: Mobile Ad Hoc NETwork Example
Chakeres, et al. Expires April 5, 2008 [Page 7]
Internet-Draft MANET Architecture October 2007
4. MANET Interface Characteristics
Inheriting from Packet Radio as described above, primary
particularities of MANETs are the characteristics and qualities of
MANET interfaces, and the challenges these entail for protocol design
and development.
4.1. Qualities - Wireless, Mobile, Ad hoc
In MANETs several qualities impact protocol design. The most
fundamental qualities are wireless interface characteristics,
mobility, and ad hoc interaction.
Wireless interfaces often exhibit more challenging characteristics
when compared to wired interfaces. Many protocols (e.g., IPv6
neighbor discovery [RFC2461]) were not designed to operate in
wireless networks with asymmetric reachability. Wireless interfaces
may also exhibit very dynamic time varying performance (e.g., packet
loss, data rate), and the factors have a significant impact on local
communication.
Mobility can also exacerbate communication issues, making it more
challenging to attain, establish, and maintain network relationships
between nodes.
Ad hoc networking further compounds problems by allowing nodes to
join and leave the network, or even form new networks, at will.
4.2. Challenges
MANET characteristics result in many challenges. These challenges
reveal themselves in many forms, and MANET specific protocols must
often be developed.
4.2.1. Semi-Broadcast Interface
Given a wireless SBI that exhibits time-varying asymmetric
reachability and spatially distributed MANET routers, each MANET
router may have a different unique partial view of the MANET. That
is, each node may see a different set of neighboring MANET routers.
Chakeres, et al. Expires April 5, 2008 [Page 8]
Internet-Draft MANET Architecture October 2007
Communication
Range
<~~~~~~~~+~~~~~~~~> <~~~~~~~~+~~~~~~~>
Single |<~~~~~~~~+~~~~~~~~>|
SBI +--|-+ +--|-+ +--|-+
|MNR1| |MNR2| |MNR3|
+----+ +----+ +----+
MNR1 MNR2 MNR3
-------------------------
Neighboring MNR2 MNR1 MNR2
Routers MNR3
Figure 4: Semi-Broadcast Interface (SBI) Neighboring Routers
The possibly unique set of neighboring MANET routers perceived by
each MANET router often requires MANET routers to send packets out
the same wireless interface as the one over which they were received.
Topologically, this act of forwarding out the same interface may
cause a packet to reach a different set of MANET routers by
traversing the wireless communication medium in a new location. An
example is provided in Figure 4, where each MANET router is capable
of reaching a different set of MANET routers.
The act of forwarding packets out of the same interface as the one
over which they were received often results in duplicate IP packets
being received by MANET routers with more than one neighboring MANET
router, while also reaching a new subset of MANET routers. Thus,
duplicate packet detection is often an inherent part of MANET
protocol designs.
4.2.2. Fuzzy Relationships Between Nearby MANET Routers & MANET
Routers' Extended Neighborhoods
Defining the process of determining neighboring MANET routers'
existence, continued existence, and loss of existence is a
fundamental challenge in MANETs. Relationships with neighboring
MANET routers are hard to define due to the MANET interface
characteristics.
Historically, two nodes are either neighbors or not neighbors and
several simple mechanisms have been used to determine neighbor
relationships: single packet reception, acceptable loss rates, and
simple handshakes. [RFC2461], for example, employs an initial
exchange of messages to determine neighborship or absence thereof.
In networks with MANET interface the types of neighbor relationships
expand, as do the mechanisms to detect and maintain the state of such
Chakeres, et al. Expires April 5, 2008 [Page 9]
Internet-Draft MANET Architecture October 2007
relationships.
Wireless network interfaces may exhibit unidirectional communication.
Dynamic wireless networks may also experience significant time
varying packet delivery between the same pair of wireless network
interfaces, so simple loss rates may not be sufficient to define a
neighbor relationship. Similarly, as nodes (and, hence, interfaces)
move relatively to each other, past loss rates may not reflect future
communication capabilities.
In MANETs' with SBI, MANET routers within the same small geographic
region are often densely connected with other nearby MANET routers.
These routers form a set of extended neighbor relationships. This
set is referred to as a MANET neighborhood. A MANET neighborhood is
typically composed of several MANET routers, with each MANET router
being densely connected to other MANET routers.
These more dynamic neighbor relationships do not sit well with
certain Internet Protocols designed assuming a fixed Ethernet like
model to communication links (bidirectional, transitive, and stable).
Given the fuzzy neighbor relationships between MANET routers, the
addressing model often associated with a Ethernet link is not
logical. For example, in an Ethernet network nodes are often told
that a particular range of addresses are "on-link". In MANETs' a
MANET router often cannot make assumptions that a particular set of
MANET routers is always (directly) reachable. Instead, MANET routers
must detect and determine neighboring MANET routers, and handle
changes to this set over time.
4.2.3. MANET Membership
Given MANETs' characteristics (mobile, wireless, ad hoc), determining
a MANETs' membership is difficult, if not impossible in certain
scenarios.
Chakeres, et al. Expires April 5, 2008 [Page 10]
Internet-Draft MANET Architecture October 2007
/----------------------\ /----------------------\
| MANET | | MANET |
| +----+ +----+ +----+ | | +----+ +----+ +----+ |
| |MNR1+-+MNR2+-+MNR3| | | |MNR1+-+MNR2+-+MNR3| |
| +-+--+ +----+ +----+ | | +----+ +----+ +-+--+ |
| | | | | |
| +-+--+ | Change | +-+--+ |
| |MNR4| | in | |MNR7| |
| +----+ | Time | +----+ |
| \ | \----------------------/
| +----+ |
| |MNR5| |
| +----+ | /----------------------\
| / \ | | MANET |
| +----+ +----+ | | +----+ +----+ +----+ |
| |MNR6| |MNR7| | | |MNR6+-+MNR4+-+MNR5| |
| +----+ +----+ | | +----+ +----+ +----+ |
\----------------------/ \----------------------/
Figure 5: MANET(s)
At one moment a MANET might consist of a certain set of nodes, and
the next the MANET could partition into several MANETs. Later it
might re-merge or merge with a new set of nodes and form a larger
MANET.
Certain routers in a MANET might connect to other routing domains.
These routers are called Border Routers (BRs), and they often run
multiple routing protocol instances. BRs are responsible for
choosing the routing information to announce between the various
attached routing domains. BRs should also present a consistent
picture of the nodes reachable through them.
As MANET membership changes, so does the connectivity of BRs within
the MANET. Therefore, a BR may be challenged to present a consistent
set of reachable nodes. It may even choose not to announce any
routing information about the MANET to other routing domains.
5. Addressing & the MANET Prefix Model
This section presents an architectural model for MANETs which
preserves the integrity of the conventional IP addressing
architecture while allowing for the particularities of MANET
interfaces.
Chakeres, et al. Expires April 5, 2008 [Page 11]
Internet-Draft MANET Architecture October 2007
5.1. General Address Architecture
This architectural model considers MANET routers as simply routers
with nodes possibly attached. These attached nodes may be attached
"behind the router"; that is, the router may be responsible for
announcing the location of a particular address or set of addresses
(i.e. a subnet prefix).
This configuration implies that, from the point of view of these
nodes and the applications running on them, they are not exposed to
the specific characteristics of MANET interfaces.
A MANET router can be delegated zero or more prefixes. For example,
if a MANET router is delegated a prefix p::, then subnet prefixes
derived from this prefix (e.g, p:1::/64, p:2::/64, ...) may be
assigned to the MANET routers' non-MANET interfaces(s), and nodes on
these interfaces may be assigned addresses from within this prefix,
and configured with this prefix according to the address
autoconfiguration mechanisms governing these interfaces ([RFC2461]
and [RFC2462]). This concept is illustrated in Figure 6.
MANET interfaces are specifically *NOT* configured with this prefix.
The configuration of these MANET interfaces is detailed in
Section 5.2.
MANET <~~~~~~+~~~~~~>
Interface | Delegated
| Prefix
''''''''''''''''''''' ==========
' MANET ' <=== P::/62 =
' Router ' ==========
''''''''' : ' Assigned
: ' : ' Prefix
: ' +--------+' ============
============ : ' |Loopback|' <=== P:1::/64 =
= : = : ' +--------+' ============
= Other = : ''''''''''''' Assigned
=Interfaces= : Prefix
============ : ============
+......+......+ <=== P:2::/64 =
: : ============
+-+-+ +-+-+
| N | * * * | N |
+---+ +---+
P:2::1 P:2::K
Chakeres, et al. Expires April 5, 2008 [Page 12]
Internet-Draft MANET Architecture October 2007
Figure 6: MANET Router and Prefixes Example
5.2. MANET Interface Configuration
MANET interface specific behaviors are exclusively exposed to the
MANET routers. These behaviors may include asymmetric reachability,
semi-broadcast interfaces, fuzzy MANET router neighbor relationships,
changing MANET membership, rapid topology dynamics, etc.
The following characteristics deserve particular mention, since they
distinguish the configuration and behavior of MANET interface(s):
Unique Prefixes
MANET interfaces that are known to exhibit the above mentioned
properties must be configured with unique prefixes. The reason
for this requirements is so that no two MANET interfaces are
configured to appear within the same IP prefix. One way to
achieve this is /128 (IPv6) or /32 (IPv4) prefixes. It is worth
noting that prefix lengths shorter than /128 (IPv6) or /32 (IPv4)
are possible on the MANET interfaces, as long as the prefixes are
unique to a single MANET interface. Note that the above
statements are not an exception, but simply a clarification that
MANET are no different from other networks in this respect.
Link-local Multicast/Broadcast Scope
On a MANET interface, a packet sent to a link-local multicast or
all-ones broadcast address reaches the MANET interfaces of
neighboring MANET routers, regardless of their configured
addresses. Link-local multicast/broadcast packets are never
forwarded and since a MANET may span several hops, nodes cannot
assume that a packet sent to a link-local multicast/broadcast
address will reach all routers within a MANET.
5.3. Routers and Hosts in a MANET
The MANET addressing model presented in this section makes a clear
separation between the role of MANET router and host in a MANET,
recognizing that:
o MANET interface characteristics are only exposed to MANET-aware
routers running appropriate protocols;
o nodes and networks/subnets on non-MANET interface(s) are not
subjected considering MANET characteristics;
o applications on hosts and protocols run unmodified.
MANET protocols are protocols developed to work on MANET interfaces
Chakeres, et al. Expires April 5, 2008 [Page 13]
Internet-Draft MANET Architecture October 2007
and to be MANET-aware. The MANET WG is chartered to develop routing
protocols for MANET interfaces. The Autoconf WG is chartered to
develop autoconfiguration protocols for MANET interfaces and MANET
routers.
Note that this addressing framework is similar to how routing in the
existing Internet is structured. Routers run their routing protocol
over router interconnects with various characteristics to which only
the routing protocols are privy. On the other hand, hosts connect to
routers over interfaces with well-defined characteristics.
6. MANETs' Place in the Network Stack
While the MANET WG is focused on network (L3) routing, that does not
imply that MANETs and their protocols are limited to L3. Several
previous and existing efforts are applying MANET protocols at various
layers. Many of the challenges discussed above (with the notable
exception being IP addressing) exist independent of at which layer
MANET protocols are deployed. Of course, the protocols themselves
may need to be retooled slightly to accommodate the information
available to the deployed layer.
One example of sub-IP MANET routing is MANET MAC layer (L2) routing.
This type of routing is often called bridging, and may work in
homogeneous wireless networks for delivering frames over multiple
hops.
L2 routing/bridging hides the multiple L2 hops from L3. This
behavior can be advantageous as this network can transparently mimic
an Ethernet, to some extent. The ability to mimic Ethernet allows
the L2 MANET to utilize existing L3 network protocols. On the other
hand, this transparency may lead to performance problems. For
example, if the L3 protocols make heavy use of broadcast messaging or
if devices assume that high-speed bandwidth resources are available.
L2 MANETs do not enable heterogeneity. That is, a L2 MANET is not
capable of bridging across heterogeneous interfaces. For example, L2
bridging cannot directly bridge two L2 technologies with different
addressing schemes. It can also be difficult if the frame sizes of
two L2 technologies vary, as this could require breaking a single
frame into multiple frames of a different format.
L3 MANETs enable heterogeneous networking, as IP was built with this
feature in mind. Forming a MANET at L3 implies that the L3 protocols
must handle the challenges presented in this document.
MANET like protocols can also be used at other layers, both above and
Chakeres, et al. Expires April 5, 2008 [Page 14]
Internet-Draft MANET Architecture October 2007
below L3. Another example is peer-to-peer (P2P) networks; these
networks have some of the same challenges as MANETs.
7. Sharing of Information Across Layers
In wireless networks, and especially in MANETs, propagation of
additional information across layers should be considered. For
example, link layer feedback that a packet/frame was not able to be
sent or that it was not received could be used by the network layer
to indicate that a neighboring MANET router is no longer reachable.
This information and other extended interfacing could reduce, or
eliminate, some upper layer messaging. Further, it could
significantly reduce the latency in decision making. Note that
though certain lower layer information is valuable, it likely needs
to be extrapolated or filtered before accurate assumptions about the
network state can be made. For example, failure to deliver a single
frame/packet by itself may not be a good indicator that a node is or
is not reachable.
In networks with several different layers of MANET mechanisms, the
sharing of information across different layers can be even more vital
to creating and maintaining the network. For example, if a P2P
network is run on top of a L3 MANET, the two networks can share
information to use a similar optimized topology, or two network can
share neighboring MANET router state changes to reduce the messaging
or the latency in making decisions.
8. Deployment Taxonomy
The present and future proliferation of inexpensive wireless
interfaces continues to stimulate technical interest and developments
in the area of MANET for a wide variety of deployment scenarios. In
this section, we present several characteristics for describing
expected MANET deployments.
8.1. Service Availability
Nodes often expect certain services/servers to be available. When
describing a deployment scenario, it is important to specify the
expected services available and the distance between the
participating nodes. In MANET, nodes might assume a service is
available locally (within one IP hop) or within a particular scope
(one or more IP hops - MANET, site, global). Nodes might assume in
certain deployments that no special servers/services are available.
Finally, nodes might assume that servers are sometimes available, but
their availability is not guaranteed or ensured.
Chakeres, et al. Expires April 5, 2008 [Page 15]
Internet-Draft MANET Architecture October 2007
Different frameworks for autoconfiguration, network management, and
routing within an Autonomous System (AS) can be developed based upon
the expected constraints and operating conditions.
8.2. Number of MANET Routers in a MANET
The number of MANET routers in a MANET routing domain is an important
consideration. This number is not the complete number of nodes in a
MANET (since MANET routers may support an arbitrary number of
connected nodes) but a measure of the number of MANET routers
participating as a cohesive flat routing domain.
While the number of MANET routers does not define scalability of a
MANET protocol, it is often useful to discuss the number of MANET
router to get a feel for maturity of typical deployment solutions.
For simplicity we define the following network sizes to aid in
discussion:
Small
2-30 MANET routers
Moderate
30-100 MANET routers
Large
100-1000 MANET routers
Very large
Larger than 1000 MANET routers
As of 2007, small and moderate size peer MANET routing scenarios have
matured and have undergone reasonable test and deployment experience.
MANETs of those sizes can perform reasonably well in many cases
without hierarchy. For scaling up to large and very large MANET
networks, routing hierarchies, a standard technique for wired
Internet routing, is a possibility. While scaling design extensions
exist, large and very large MANET flat routing domains are still a
topic of ongoing active research and are not discussed further here.
9. Security Considerations
Each MANET router may not know its neighborhood a priori
(Section 2.2), but it should determine its neighborhood dynamically
and track changes as the network evolves. Similarly for MANET
network membership (Section 4.2.3), MANET routers may leave or join a
MANET, and the MANET may partition or merge with others. In addition
to these issues, many MANET routers are expected to communicate over
Chakeres, et al. Expires April 5, 2008 [Page 16]
Internet-Draft MANET Architecture October 2007
wireless interfaces; and the "open" nature of wireless communication
means that nearby nodes will often be capable of sending and
receiving MANET protocol packets.
Without any security measures MANET routers operating under these
characteristics will often expose protocol information to and accept
information from nearby nodes. Protecting MANET routers from
disruptive nearby nodes can be performed by using confidentiality,
data integrity, and peer entity authentication.
Different deployments of MANETs may have very different security
requirements. For example, if a MANET is deployed for a military
purpose, exposing the network topology to any outside party may not
be acceptable -- whereas for a civilian deployment exposure of
topology information may be of little or no importance. Furthermore,
different deployments may require different mechanisms to address
security issues (e.g., pre-sharing of keys or certificates), and the
MANET routers themselves may have various additional constraints
(e.g., computational power for generating or verifying cryptographic
attributes). Therefore, due to the large diversity of MANET routers
and their deployments, MANET protocols should allow for appropriate,
and possibly multiple or various, security mechanisms.
10. IANA Considerations
This is an informational document. IANA requirements for MANET
related protocols will be developed within the protocol
specifications for MANET protocols.
11. Acknowledgments
Discussions and developments concepts and architectural issues have
evolved over many years of discussion of related work within the
MANET WG. There are obviously many people that have contributed to
past discussions and related draft documents within the WG that have
influenced the development of these concepts that deserve
acknowledgment. The authors would like to thank all contributors to
the MANET and AUTOCONF WG efforts and those that have helped in the
review and content process.
While not entirely complete the authors would like to in particular
thank the following individuals for exhaustive discussions and
valuable contributions:
Jari Arkko
Chakeres, et al. Expires April 5, 2008 [Page 17]
Internet-Draft MANET Architecture October 2007
Emmanuel Baccelli
Alan Cullen
Justin Dean
Christopher Dearlove
Tom Henderson
Bob Hinden
Thomas Narten
Charles Perkins
Subhranshu Singh
Fred Templin
Dave Thaler
Seung Yi
12. Informative References
[DWN03] Macker, J. and S. Corson, "Mobile Ad hoc Networking:
Routing Technology for Dynamic, Wireless Networks", IEEE
Press, Mobile Ad hoc Networking, Chapter 9, 2003.
[FL01] Freebersyser, J. and B. Leiner, "A DoD perspective on
mobile ad hoc networks", Addison Wesley C. E. Perkin, Ed.,
2001, pp. 29--51, July 2001.
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2453] Malkin, G., "RIP Version 2", STD 56, RFC 2453,
November 1998.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
Chakeres, et al. Expires April 5, 2008 [Page 18]
Internet-Draft MANET Architecture October 2007
December 1998.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC2501] Corson, M. and J. Macker, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501, January 1999.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
June 2007.
Authors' Addresses
Ian D Chakeres
Motorola
Bagmane Tech Park
66/1, Plot 5, CV Raman Nagar
Bangalore, Karnataka 560093
India
Email: ian.chakeres@gmail.com
URI: http://www.ianchak.com/
Joe Macker
Naval Research Laboratory
Washington, DC 20375
USA
Email: macker@itd.nrl.navy.mil
Thomas Heide Clausen
LIX, Ecole Polytechnique
91128 Palaiseau CEDEX
France
Email: T.Clausen@computer.org
URI: http://www.thomasclausen.org/
Chakeres, et al. Expires April 5, 2008 [Page 19]
Internet-Draft MANET Architecture October 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Chakeres, et al. Expires April 5, 2008 [Page 20]