Internet DRAFT - draft-sethom-adhoc-gateway-selection
draft-sethom-adhoc-gateway-selection
Internet Draft Kaouthar Sethom
INT-France
Hossam Afifi
Document: draft-sethom-adhoc-gateway- INT-France
selection-01.txt Frank Y. Li
Expires: June 2006 UniK, Norway
Andreas Hafslund
Thales,Norway
January 2006
Gateway Selection in Multi-homed Ad Hoc Networks
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Gateway Selection in Multi-homed Ad Hoc Networks January 2006
Abstract
When an ad hoc network is connected to the Internet, it is important
for the mobile nodes to detect available gateways providing access to
the Internet. Therefore, a gateway discovery and selection mechanism
is required. Current ad hoc routing protocols have been extended to
support gateway discovery. However, the selection process is based on
the default gateway configuration. We here describe an extension to
MANET protocols to enable the gateway selection according to users’
requirements, especially in the case where multiple gateways co-
exist.
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 RFC-2119.
Table of Contents
1. Introduction...................................................2
2. Terminology ...................................................4
3. Protocol overview..............................................4
3.1 GNA Message Format.........................................5
4. Addressing and auto-configuration considerations .............7
5. IPv6 Considerations............................................8
6.Security Considerations.........................................8
References........................................................8
Authors’ Addresses................................................9
1. Introduction
An ad hoc network is a highly dynamical wireless network without the
use of any existing network infrastructure or centralised
administration. An ad hoc network can operate either in a stand-alone
mode or as a subnetwork to the global Internet. In the latter case,
an ad hoc user does not only demand for Internet connectivity but
also a certain level of QoS. To provide this connectivity, some ad
hoc nodes act as “gateways” which can be used by mobile terminals to
seamlessly communicate with other nodes in external networks.
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Gateway Selection in Multi-homed Ad Hoc Networks January 2006
Therefore, a user – even inside an ad hoc network - must be able to
discover the gateway, and/or to select an optimal gateway in the
presence of multiple gateways, according to its application
requirements.
In a simpler case where there is only one gateway available, the
problem is simply how to discover the gateway and configure a
globally valid address to the mobile node for incoming and outgoing
traffic. In a more complicated case where several gateways co-exist,
i.e., for multi-homed ad hoc networks, the availability of multiple
gateways provides the network with higher robustness and more
flexibility for global Internet connectivity. Therefore, it is
important, especially for a multi-homed network, to discover and
select a gateway that is the ‘optimal’ one among all available
gateways, according to certain criteria.
Methods for Internet gateway discovery include reactive [1],
proactive [2], or hybrid [3] approach. For multi-homed ad hoc
networks, one specific problem is related to which gateway(s) a node
should use. The challenge stems from the need to inform ad hoc nodes
about available gateways and their associated capabilities in an
infrastructure-less and extremely dynamic environment. A
straightforward solution for gateway selection is to select the
gateway that has the shortest number of hops to the mobile node as
the ‘working’ gateway. This means that when a mobile node is closer
to a new gateway than the previous one, the mobile node will usually
switch to the second gateway for the global connectivity. If the
mobile node already has a data connection up and running, this can
impose problems. This is especially true when the gateways have
deployed NAT or some specific security mechanisms. Mechanisms for
gateway connection in multi-homed proactive ad hoc networks were
discussed in [4]. Generally speaking, selecting a gateway based on
only the shortest number of hops does not appear to be good enough.
Another alternative is to consider both the distance in number of
hops between mobile nodes and gateways and the traffic load of
available gateways. The one that has the minimum weighted sum of
Euclidean distance for these two factors will be selected as the
gateway [5]. Other considerations for gateway selecting include load
and congestion status in the gateways, delay for certain types of
traffic flow, session continuity when shifting gateways etc.
In this draft, we present a gateway selection protocol for multi-
homed ad hoc networks. Other issues related to multi-homing for a
MANET, such as addressing and auto-configuration, NAT deployed on the
gateways, the use of Mobile IP, and security mechanisms, are not
addressed in this draft.
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2. Terminology
Multi-homed ad hoc network
An ad-hoc network which has more than one gateway connecting it to
the global Internet.
3. Protocol overview
When a node wishes to offer Internet connectivity to other nodes in a
MANET, it sends (or disseminates) Gateway and Network Association
(GNA) messages. In the case of a proactive routing protocol this is
done periodically. A selected set of nodes that received a GNA
packet shall forward it to their neighbours. GNA message is in this
way flooded onto the entire ad hoc network. Duplicate retransmissions
will be eliminated locally (i.e., each node maintains a duplicate
table to prevent transmitting the same message twice). However, in
the case of a reactive protocol the generation of GNA message is
generally in response to some previous gateway discovery request
message. The GNA message follows then down the reverse path of the
associated request to reach the querying node.
At each node in the network, all received GNA packets are registered
in the gateway table. This information repository is re-freshed
periodically. This means that entries are deleted as soon as their
validity time expires.
GNA routing is done hop-by-hop. This means that when A (Figure 1)
receives from B a GNA announcing connectivity to the Internet. It
adds a route in its gateway table with the next-hop on the route to
the gateway i.e B as the actual gateway and a route metric equal to
2.
A --- B --- G ------ Internet
Figure 1: GNA routing
When a GNA message is received, the node updates its gateway table
either by updating an existing entry, or if no entry exists for the
gateway address, creating a new entry.
All nodes in the ad hoc network must support GNA processing and route
calculation for the actual GNA routing to work. If a node routes
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Gateway Selection in Multi-homed Ad Hoc Networks January 2006
Internet traffic to an intermediate neighbor based on GNA
information, the intermediate neighbor must also have set up an
Internet route for the traffic to be routed. Therefore, in the
general case, the neighbor must support GNA functioning.
The present document is presented with IPv4 addresses. Considerations
regarding IPv6 are given in section 5.
3.1 GNA Message Format
A GNA message contains triplets of (router interface characteristic,
network address, netmask).
The proposed format of an GNA-message is (omitting IP and UDP
headers):
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Message Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | Vtime | Time To Live | Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Interface Type| Cost | Throughput |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Netmask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Interface Type| Cost | Throughput |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Netmask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
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Length The length (in bytes) of the packet
Sequence Number The Message Sequence Number MUST be incremented
by one each time a new GNA message is
transmitted. A separate Packet Sequence Number
is maintained for each interface such that
packets transmitted over an interface are
sequentially enumerated.
Message Type Set to GNA_MESSAGE
Vtime This field indicates for how long time after
reception a node MUST consider the information
contained in the message as valid, unless a
more recent update to the information is
received.
TTL field May be set from 1 to 255.
Hop Count This field contains the number of hops a message
has attained. It’s particularly interesting to
have this information in the case of an adhoc
network; to know how far the gateway is.
Initially, this is set to '0' by the originator
of the message
Originator Address This field contains the address of the node,
which has originally generated the GNA
message i.e the gateway. This field SHOULD NOT
be confused with the source address from the IP
header, which is changed each time to the
address of the intermediate interface which is
re-transmitting this message. The Originator
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Address field MUST *NEVER* be changed in
retransmissions
Interface Type This field indicates the technology used by the
gateway Egress interface. Example Bluetooth,
802.11, Ethernet, UMTS …
Type values can be encoded as follows:
0x00 Ethernet (default)
0x01 Bluetooth
0x10 UMTS
0x11 802.16
…
Cost This field indicates the communication cost
associated with the use of the interface
described in the interface Type field. This
parameter can be a combination of different
metrics such as offered QoS, security issues,
price and possibly other preferences.
Throughput This field indicates the throughput associated
with the gateway egress interface i.e. nominal
bandwidth/capacity/datarate.
Network Address The network address associated with the egress
interface described in the interface Type field.
Netmask The netmask, corresponding to the network
address immediately above.
4. Addressing and auto-configuration considerations
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When a mobile node has discovered a gateway, it will need to
configure an address related to this gateway. Many suggestions assume
that the mobile node will need to configure an address from the
gateway’s network prefix. In this way, the node will be in an address
subnetwork of that gateway. This new address must then be inserted
into the ad hoc routing so the node is reachable on this address. The
mobile node should also be reachable on other temporary addresses,
and its home address. This imposes several more problems for the ad
hoc routing. There exist several Internet-Drafts, e.g., [6][7], on
addressing and auto-configuration in MANETs. Therefore, these issues,
although closely associated with the gateway selection problems, are
not discussed in this draft.
5. IPv6 Considerations
All the operations and parameters described in this document used by
GNA for IP version 4 are the same as those used by GNA for IP version
6. To operate with IP version 6, the only required change is to
replace the IPv4 addresses with IPv6 addresses.
6. Security Considerations
This memo does not specify any security considerations.
References
[1] J. Jonsson, F. Alriksson, T. Larsson, P. Johansson, and G.
Maguire, “MIPMANET – Mobile IP for Mobile Ad Hoc Networks”,
Proceedings of the first ACM Annual Workshop on Mobile Ad Hoc
Networking and Computing (MobiHoc), 2000.
[2] T. Clausen, and P. Jacquet, “Optimized Link State Routing
Protocol”, RFC 3626, IETF, October 2003.
[3] P. Ratanchandani, and R. Kravets, “A Hybrid Approach to
Internet Connectivity for Mobile Ad Hoc Networks”, Proceedings
of IEEE Wireless Communications and Networking Conference
(WCNC), March 2003.
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[4] P. Engelstad, A. Tønnesen, A. Hafslund, and G. Egeland,
”Internet Connectivity for Multi-Homed Proactive Ad Hoc
Networks”, Proceedings of the IEEE Int. Conf. on
Communications (ICC), June 2004.
[5] H. Ammari and H. El-Rewini, “Using Hybrid Selection Schemes
to Support QoS when Providing Multihop Wireless Internet
Access to Mobile Ad Hoc Networks”, Proceedings of the First
IEEE Int. Conf.on Quality of Service in Heterogeneous
Wired/Wireless Networks (QSHINE), Oct. 2004.
[6] C. Adjih, S. Boudjit, P. Jacquet, A. Laouiti, and P.
Muhlethaler, “Address autoconfiguration in Optimized Link
State Routing Protocol”, Internet-Draft (draft-laouiti-manet-
olsr-address-autoconf-00.txt), work-in-progress, Feb. 2005.
[7] T. Clausen, and E. Baccelli, “Simple MANET Address
Autoconfiguration”, Internet-Draft (draft-clausen-manet-
address-autoconf-00.txt), work-in-progress, Jan. 2005.
Authors’ Addresses
Kaouthar Sethom
INT-France
9 rue charles fourrier 91011 evry cedex France
Email: kaouthar.sethom@int-evry.fr
Hossam Afifi
INT-France
9 rue charles fourrier 91011 evry cedex France
Email: hossam.afifi@int-evry.fr
Frank Y. Li
UniK – University Graduate Center
N-2027 Kjeller
Norway
Email: frank.li@unik.no
Andreas Hafslund
Thales Norway AS
P.O Box 22 Økern
N-0508 Oslo, Norway
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Email: andreha@unik.no
Copyright (C) The Internet Society (2006)
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