AU1669701A

AU1669701A - A method of routing messages in an ad hoc network

Info

Publication number: AU1669701A
Application number: AU16697/01A
Authority: AU
Inventors: Benoit Fabre
Original assignee: Alcatel CIT SA; Alcatel SA
Current assignee: Alcatel Lucent SAS
Priority date: 2000-02-03
Filing date: 2001-01-29
Publication date: 2001-08-09
Also published as: FR2804815B1; CA2332483A1; FR2804815A1; EP1122919A1; JP2001274815A

Description

P/00/01i1 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: A method of routing messages in an ad hoc network The following statement is a full description of this invention, including the best method of performing it known to us: FHPqYlCFNATW12r(n) U2 A I 1 A METHOD OF ROUTING MESSAGES IN AN AD HOC NETWORK The present invention relates to a method of routing messages in a network whose topology is not known to its nodes. The invention relates in particular to networks referred to as ad hoc networks.

BACKGROUND OF THE INVENTION An ad hoc network is a network whose, topology (i.e.

the configuration of the connections between its elements) can change with time. This is typically the case with a network whose elements (or nodes) are mobile and connected by radio links. Because of this mobility, the topology of the network is not fixed and therefore cannot be known at all times. Consequently, routing a message in the network is a problem and this problem cannot be solved by standard routing algorithms.

A first example is that of rapid deployment networks, such as those used during emergency operations following a disaster (fire, flood, etc.) that may have rendered the usual telecommunications network unserviceable. Such occurrences can necessitate the rapid deployment of a new mobile radio network whose base transceiver stations may be on vehicles, for example, and therefore move around relative to one another.

0Another example is that of new generation mobile radio networks such as GSM networks. In existing networks the base transceiver stations are fixed. This 0oooo0 0gives rise to the problem of "shadow areas", i.e.

geographical areas which are not covered by a base transceiver station because a building or hill, for S 30 example, forms an obstacle to the propagation of radio waves. To cover these shadow areas, consideration might be given to having some or all of the mobile terminals behave as mobile base transceiver stations or at least as relay stations between the fixed base transceiver stations and other mobile terminals.

A third example is that of satellite networks, for example constellations of non-geostationary satellites with links between satellites (which can be regarded as base transceiver stations). In this case, however, although the topology of the network varies with time, the evolution is predictable, making the problem less complex.

Clearly, in a network of this kind, a path set up at time t between two nodes (terminals, base,transceiver stations, etc.) may no longer be valid, or at least may no longer be the optimum, at time t+At.

Solutions employing routing tables, for example those used in IP (Internet Protocol) type protocols, therefore cannot be used.

The article "A New Routing Protocol for the Reconfigurable Wireless Network" by Zygmunt J. Haas; ICUPC'97, San Diego, October 1997, describes a protocol for routing messages across an ad hoc network of the above kind which is usually referred to as the zone routing protocol (ZRP). The same..protocol was disclosed one month later, in November 1997, in the form of an "Internet Draft" entitled "The Zone Routing Protocol (ZRP) for Ad Hoc Networks". Its authors are Zygmunt J.

Haas and Marc R. Pearlman.

From the point of view of a node, the network is "divided into two domains, namely its vicinity and everything outside its vicinity. The vicinity is made up of all the nodes to which it knows how to route a message. The domain consisting of everything outside its vicinity is of course made up of all the nodes (other than the node in question) not in its vicinity.

30 A distance within the network is defined as the minimum number of connections between two nodes.

The radius of the vicinity is the maximum distance, expressed as a number of connections, between the node concerned (at the center of the vicinity) and nodes at the boundary of the vicinity.

The area referred to as the boundary of the vicinity is defined by the nodes situated at a distance from the node concerned equal to the radius of the vicinity.

Figure 1 illustrates these concepts and represents a network including a set of interconnected nodes N to N 34 This example is described from the point of view of node

N

17 The nodes are considered to have a vicinity of radius 2 delimited by curved line V.

The vicinity defines a set of nodes N 6

N

7

N

8

N

19

N

2 0

N

30

N

24

N

15 and N 12 which are located at the boundary.

According to the definitions previously stated, the node N 17 is aware of the existence only of nodes within the curved line V.

To route a message from a first node (N 17 to a second node (for example N 21 the ZRP first determines whether the second node is in the vicinity of the first node. If not, the message to be routed is transmitted to the nodes at the boundary of the vicinity of the first node.

Each of those nodes has its own vicinity. The method just described is reiterated for each vicinity.

The message therefore propagates across the network and normally reaches the second node in due course.

For example, the message is sent first to the nodes *oo at the boundary of the vicinity of node N 17 The nodes it reaches include node N 19 which has its own vicinity which includes node N 2 1. The required path is then the concatenation of the paths from node N 17 to node N 19 and from node N 19 to node N 21 The method used to find the path from one node to a S 30 node in its vicinity is more conventional and can be a o° o "prior art method. However, because of the general context in which the method is used, some methods are more appropriate than others.

The method chosen is used both to route the message to the destination node when it is in the vicinity of an intermediate node and also to route the message from an intermediate node to the nodes at the boundary of its vicinity.

The message can be a path-seeking message, meaning that it is used to establish a path between the first and second nodes. On receiving a path-seeking message of this kind, the second node (the destination of the message) sends a response to the first node which therefore acquires knowledge of the path used for the message. To this end, the message contains a list of the nodes it has passed through.

The first node is therefore in a position to send new messages to the second node using a communications protocol enabling calls in connected mode, meaning that all the messages belonging to the same call will use the same path as determined in this way.

For example, the path can be indicated in the header of the message, or each node on the path can store the path for correct routing of messages requiring to use it.

The message could also be a message conveying information addressed to the second node for a purpose other than setting up a path. For example, it could be a call in non-connected mode, i.e. in which each message sent requires the path connecting the sender to the receiver to be redetermined.

S" According to the ZRP, as disclosed in the aforementioned documents, the number of messages is minimized by avoiding the same intermediate node sending the same message more than once.

Figure 1 attempts to clarify this mechanism.

Initially the message is sent to nodes which include 30 nodes N 8 and N 19 at the boundary of the vicinity of node

N

17 On receiving this message, node Ns (for example) also considers its own vicinity and forwards the message to the nodes at its boundary, and therefore to node N 19 (it can be shown that nodes N 8 and are a distance 2 apart). Consequently, node N 8 sends the message to node

N

19 which therefore receives it twice.

Using the same reasoning, it can be shown that the same node can in fact receive the same message several times, which leads to overloading of the ad hoc network and catastrophic deterioration of its performance.

To solve this problem, information on messages sent and received is stored in each node. Thus when a message is received, the node can look up this information to determine if an identical message (same content, same destination, etc) has already been received. If so, the received message is not forwarded again.

The applicant does not concede that the prior art discussed in the specification forms part of the common general knowledge in the art at the priority date of this application.

Summary of the invention The above-proposed solution to the problem of minimising the number of messages transmitted leaves a deal to be desired. An object of the present invention is therefore to reduce further the number of messages transmitted within the network.

In a first aspect, the invention provides a method of routing a message from a first node to a second node via a set of intermediate nodes. Each node is aware only of nodes in its vicinity. The first node and each of the intermediate nodes implement the following steps: testing if the second node is part of the vicinity, and if it is not o* sending the message to a set of nodes at the boundary of the vicinity via a set of adjoining nodes.

In the method, the set of adjoining nodes is determined by a list of node identifiers in the message and before sending the message the intermediate node adds to the list the identifiers SO of the nodes of the set of adjoining nodes.

The set of nodes to which the message is sent is therefore reduced by using this list of the identifiers of the nodes to which the message is sent. This reduction indirectly reduces the number of messages in the network, which improves the performance of the network.

The invention also provides a telecommunications network node including: means for receiving a message addressed to a destination node, means for testing if the destination node is in its vicinity, and means for sending the message to a set of nodes at the boundary of the vicinity via a set of adjoining nodes.

The node further includes means for adding the identifiers of the nodes of the set of adjoining nodes to a list in the message before it is sent.

BRIEF DESCRIPTION OF THE DRAWINGS The invention and other advantages of the invention will be better understood on reading the following description, which is given with reference to the accompanying drawings.

Figure 1, already commented on, represents a network in which the method of the invention can be used.

Figure 2 shows a trivial application of the method of the invention and demonstrates one advantage thereof.

Figure 3 is a schematic representation of one step S"of the method of the invention.

MORE DETAILED DESCRIPTION "When a node receives a message to be routed, and if that node is not the final destination of the message, it first tests if the final destination is in its vicinity.

If so, it is sufficient to forward the message to the final destination. If not, the method of the invention sends the message to a set of nodes at the 30 boundary of the vicinity of the node. To this end, and as in the prior art, the node first transmits the message to a set of adjoining nodes, specifying in the message the nodes that it has to reach.

There are many prior art methods of routing a message from a first node to a second node when the network connecting them is known.

The invention can use any of these prior art methods.

A standard method is described in the article "A New Routing Protocol for the Reconfigurable Wireless Network" by Zygmunt J. Haas, previously cited.

That method is based on seeking the shortest path expressed as a number of hops the number of connections between nodes that the message must use).

The performance of the method can be significantly improved by using routing criteria such as: The size of the queues. To determine the size of the queues of the nodes in its vicinity, a node can send them update messages, as described in the document by Zygmunt J. Haas previously cited.

The energy of the nodes. In an ad hoc network, the problem of the autonomy of the nodes often arises. It is beneficial to give priority to the nodes having the greatest available energy.

The stability of the nodes. The less a node moves around geographically, the less the topology which links it to the other nodes changes in the short-term. Also, to minimize control message overloads if a link is down, it is preferable to give the most stable nodes priority over those moving quickly.

The above criteria, and others, can be used separately or in combination to optimize the routing of a message in the vicinity of the sending node.

Figure 2 illustrates a trivial application of the mechanism according to the invention, consisting in 30 adding to a list contained in the message the identifiers of the nodes to which the message is to be sent.

This example uses three nodes D, C and A. Despite its simplicity, the example illustrates the mechanisms of the invention and its advantages over the prior art.

It is assumed that node D transmits a message mDA to node A and a message mDC to node C.

According to the invention, the identifiers of nodes 8 C and A are added to a list of node identifiers in the messages before the messages are sent. Thus each of the two destination nodes A and C receives a message containing those identifiers.

Nodes A and C are connected to each other and constitute adjoining nodes. Each of them could be caused to send a message to the other using a prior art algorithm. Node A could send a message mAC to node C and, reciprocally, node C could send a message mCA to node A.

However, to determine the set of nodes to which the message is to be sent, the invention tests if those nodes are included in the list in the received message. If so, no message is exchanged between nodes A and C.

Compared to the prior art solution, this saves sending two messages (mAc and mcA).

Figure 3 shows the method according to the invention implemented in a very small network and illustrates the mechanisms of the invention. Figure 2, already commented i on, is in fact an extract from Figure 3.

Assume that node G wishes to route a message to node K and that the nodes have vicinities of radius 2.

The vicinity of node G comprises nodes D, I, C, A and H. The nodes at the boundary of that vicinity are S" nodes C, A and H.

These three nodes C, A and H can be reached via node D or node I and it is immaterial which of those nodes is **used.

The list of node identifiers in the message is empty at this stage.

30 There are various methods of choosing a routing within a vicinity, as previously explained. In this example it is assumed that the message is sent to node D.

The invention therefore sends the message to node D after adding its identifier to the list of identifiers in the message.

The nodes at the boundary of the vicinity of node D are nodes F, B and H.

Because node E is not in its vicinity, node D is unaware that nodes F and B are connected via node E. The adjoining nodes to which it can send a message are nodes C and A. Only node C can reach node F and only node A can reach node H.

As neither the identifier of node C nor that of node A is in the list in the message received by node D, the latter: adds the identifiers of nodes C and A to the list in question, and then sends the message containing the modified list to nodes C and A.

Node C therefore receives a message from node D.

The nodes at the boundary of the vicinity of node C are nodes G, I, H and E. To reach those nodes, it would have to send messages via the adjoining nodes F, A and D.

Nodes A and D are in the list in the message received .ee* from node D. Node C therefore adds the identifier of :2 node F to the list and then sends the message containing the modified list to node F.

In parallel with this, node A receives a message from node D. The nodes at the boundary of the vicinity of node A are nodes G, I, F and E. To reach those nodes, it would have to send messages via the adjoining nodes D, H, B, C. Node D is in the list contained in the message received from node D. Node A therefore adds the identifier of node B and then sends messages containing the modified list to nodes B and H.

In turn, node F receives a message from node C.

30 Node K, the final destination of the message, is in the vicinity of node F.

At this stage, a method of routing in a vicinity as previously explained can be used to route the message to its final destination.

An additional feature of the invention, intended to prevent a message sent in the wrong direction continuing to propagate, is that it stops sending a message if a particular criterion is reached. The criterion can be a time limit (number of minutes), for example, or a number of "hops", i.e. the number of times it has been sent.

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Claims

1. A method of routing a message from a first node to a second node via a set of intermediate nodes wherein each node is aware only of nodes in its vicinity and said first node and each of said intermediate nodes implement the following steps: testing if said second node is part of said vicinity, and if it is not sending said message to a set of nodes at the boundary of said vicinity via a set of adjoining nodes, wherein said set of adjoining nodes is determined by a list of node identifiers in said message and wherein before sending said message said intermediate node adds to said list the identifiers of the nodes of said set of adjoining nodes.

2. A method according to the preceding claim, wherein said message is a path-seeking message used to create a path between said first node and said second node. 20

3. A method according to either preceding claim, in which a message is not sent if a particular criterion is reached.

4. A telecommunications network node including: means for receiving a message addressed to a destination node, means for testing if said destination node is in its vicinity, and means for sending said message to a set of nodes at the boundary of said vicinity via a set of adjoining nodes, said node further including means for adding the identifiers of the nodes of said set of adjoining nodes to a list in said message before it is sent.

A computer program including instructions adapted to implement a method according to any of claims 1 to 3 when said computer program is executed on a computer.

6. A storage medium containing instructions adapted to implement a method according to any of claims 1 to 3 when said instructions are executed on a computer.

7. A method of routing a message substantially as herein described with reference to the accompanying drawings.

8. A telecommunications network node substantially as herein described with reference to the accompanying drawings. Dated this 29th day of January 2001 ALCATEL by its attorneys Freehills Carter Smith Beadle *l