MANET Autoconfiguration (AUTOCONF) S. Singh
Internet-Draft A. Bhatia
Intended status: Informational Samsung India
Expires: December 9, 2008 June 07, 2008
IP Link Model for MANET
draft-singh-autoconf-linkmodel-00
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Abstract
The stateless as well as stateful address autoconfiguration
Protocols, as specified by the IETF, supports links with different
properties. However, often these protocols assume specific
properties and behavior from the underlying link type, as for example
link-layer multicasting. The solution designer and implementers
consider these specific link behavior while designing or extending
these protocols. IETF Autoconf WG goal is to standardize mechanism
for address autoconfiguration of nodes in a Mobile Ad Hoc Network
(MANET). Before designing such protocol, the link model for MANET as
seen by the IP needs to be clearly understood . However, there is no
document describing IP link model for MANET. This document is an
attempt to bridge this gap.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. IP Link Model for MANET . . . . . . . . . . . . . . . . . . . . 4
3.1. Multi-access Link Model . . . . . . . . . . . . . . . . . . 4
3.2. Sub-IP Link Model . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
5. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 7
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1. Introduction
The stateless as well as stateful address autoconfiguration Protocols
[ADDRCONF],[DHCP] supports links with different properties. However,
often these protocols assume specific properties and behavior from
the underlying link type, as for example link-layer multicasting.
The solution designer and implementers consider these specific link
behavior while designing or extending these protocols. IETF Autoconf
WG goal is to standardize mechanism for address autoconfiguration of
nodes in a Mobile Ad Hoc Network (MANET). Before designing such
protocol, the link model for MANET as seen by the IP needs to be
clearly understood. However, there is no document describing IP link
model for MANET. This document is an attempt to bridge the gap.
Section 2 provides terminologies which are used in this document.
Section 3.1 details IP multi-access link model for MANET. Section
3.2 details sub-IP link model for MANET.
2. Terminology
Node a device that implements IP.
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-layer (or higher-
layer) "tunnels", such as tunnels over IPv4 or IPv6 itself.
non-broadcast multi-access (NBMA) a link to which more than two
interfaces can attach, but that does not support a native form of
multicast or broadcast (e.g., X.25, ATM, frame relay, etc.).
shared media a link that allows direct communication among a number
of nodes, but attached nodes are configured in such a way that
they do not have complete prefix information for all on-link
destinations. That is, at the IP level, nodes on the same link
may not know that they are neighbors; by default, they communicate
through a router.
Router a node that forwards IP packets not explicitly addressed to
itself.
MANET Router A router that participates in MANET routing protocols
such As [AODV],[OLSR].
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Subnet generally refer to a topological area that uses the same
address prefix, where that prefix is not further subdivided except
into individual addresses.
3. IP Link Model for MANET
This section provides detail of link model for MANET as seen by the
IP. Two possible models have been explained: multi-access link model
and sub-IP link model. Multi access link model is commonly assumed
by the MANET community while designing and implementing MANET
protocols. The sub-IP link model came into discussion multiple times
in the Autoconf WG as an alternative approach.
3.1. Multi-access Link Model
In this model there are forwarding nodes called MANET Routers which
participate in the MANET routing protocol e.g. [AODV],[OLSR]. There
may be non-MANET nodes (clients or routers) attached to non- MANET
interface e.g., via wired Ethernet. Collection of these MANET
routers constitute a Mobile Ad Hoc Network (MANET). MANET is bounded
by the MANET Border Router and is considered as a site with multiple
subnets where subnet is a topological area that uses the same address
prefix. From the IP perspective, MANET is a cloud of links where
link is considered as a topological area bounded by routers that
decrement IPv4 TTL or IPv6 Hop Limit when forwarding IP packets.
MANET nodes are often wireless and mobile. Besides, nodes may join,
leave and form network in an ah hoc manner. The set of all the nodes
on the same link receive the link-local messages and are able to
communicate with each other at the link layer. This implies that the
MANET links have the same properties as shared media [SH-MEDIA].
Moreover, asymmetric and non-transitive wireless media
characteristics result in dynamic link i.e. the set of nodes on a
particular link as well as the number of links changes with time.
Here, set of one hop neighbors and on-link nodes are not equivalent
because some nodes in a one hop neighbor set may not be able to
directly communicate due to non transitive physical link
characteristics. Hence the set of on-link nodes is always subset of
one hop neighbor set.
In MANET, some of the protocols may require MANET wide communication,
For example Duplicate Address Detection. Since multi access link
model does not consider whole MANET as one link, the protocol
developer or designer has to provide some solution for MANET wide
communication. How to perform site scoped multicast communication is
out of scope of this document and should be considered during the
solution space discussion.
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As discussed before, in this model set of on-link nodes may not be
same as set of neighbor nodes. To have these two sets equivalent,
either underlying physical link can be enhanced for transitiveness
through abstraction layer or all the on-link nodes should have the
same neighbor cache entries.
Also, issues with the shared media and asymmetric reachanbility needs
to be considered while designing any solution with this model
assumption.
3.2. Sub-IP Link Model
In this model, MANET is a multi hop network bounded by MANET routers
and from the IP perspective considered as a single link. With this
link model MANET may be considered as NBMA network and may be used to
emulate the services provided to the IPv6 layer by conventional
broadcast media such as Ethernet. Since link is considered as a
topological area bounded by routers that decrement IPv4 TTL or IPv6
Hop Limit when forwarding IP packets, therefore in order for IP to
see MANET as single link, the forwarding plane needs to work below IP
and MANET routers are required to be configured to operate at the sub
IP layer.
MANET nodes are often wireless and mobile but these characteristics
does not change the set of nodes seen by IP on a particular link.
IEEE 802.11s is an example of sub-IP model where multi-hop forwarding
is done at L2. However this approach does not address the scenario
where MANET consists of heterogeneous access technologies i.e. this
approach is suitable only for network with homogeneous link
technology. Besides, this model may have performance issues if IP
protocols make heavy use of link local multicasting.
This model could also be realized by providing sub-IP abstraction
layer such that IP is unaware of Ad-hoc, wireless and mobile
characteristics of MANET. One possible concern with this approach is
loss of end to end transparency due to link enhancement provided by
IP sub layer.
4. Security Considerations
TBD
5. Normative References
[ADDRCONF]
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Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862", Sep 2007.
[DHCP] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6), RFC 3315", July 2003.
[AODV] Perkins, C., Belding Royer, E., and S. Das, "Ad hoc On-
Demand Distance Vector (AODV) Routing, RFC 3561",
July 2003.
[OLSR] Clausen, T. and P. Jacquet, "RFC 3626 - Optimized Link
State Routing Protocol (OLSR), RFC 3626", Oct 2003.
[NDP] Narten, T., "Neighbor Discovery for IP version 6 (IPv6),
RFC 4861", Sep 2007.
[MANET-Arch]
Chakeres, I. and J. Macker, "Mobile Ad hoc Network
Architecture", IETF Draft", Dec 2007.
[SH-MEDIA]
Barden, B., Postel, J., and Y. Rekhter, "Internet
Architecture Extensions for Shared Media", RFC 1620",
May 1994.
Authors' Addresses
Shubhranshu Singh
Samssung India
Bangalore,
India
Email: Shubranshu@gmail.com
Ashutosh Bhatia
Samsung India
Bangalore,
India
Email: Ashutosh.bhatia.iisc@gmail.com
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