EP1817880A1

EP1817880A1 - Method and system for the dynamic adaptation of service quality metrics in an ad hoc network

Info

Publication number: EP1817880A1
Application number: EP05818916A
Authority: EP
Inventors: Yvon Gourhant; Djamal-Eddine Meddour; Laurent Reynaud
Original assignee: France Telecom SA
Current assignee: Orange SA
Priority date: 2004-12-01
Filing date: 2005-11-30
Publication date: 2007-08-15
Also published as: CN101069392B; CN101069392A; WO2006059040A1; FR2878674A1; US20090122748A1

Abstract

The invention relates to a method and system for the dynamic management of service quality metrics in an ad hoc network comprising a plurality of routing nodes (100) which are used to route data packets. The inventive system also comprises a network manager (200) which is used to determine, calculate and deploy a service quality metric to be applied at a given moment, based on the quality of service available on the network and on the quality of service required by one or more applications. Each node comprises a metric manager (111) which is used to update the routing table (1121) of the nodes as a function of the received service quality metric to be applied.

Description

METHOD AND SYSTEM FOR DYNAMIC METRIC QUALITY SERVICE ADAPTATION IN AN AD HOC NETWORK

Field of the invention and prior art

The present invention relates to the field of routing with quality of service in so-called "ad hoc" networks. Ad hoc networks are communication networks, using the radio medium. They consist of mobile and / or fixed nodes having the property of constituting automatically and dynamically a network capable of conveying packets from one point of the network to another when a radio communication is established between a node and his neighbors.

In an ad hoc network, packets are transmitted directly between the source node and the destination node if the destination node is in the connectivity area of the source node or through neighboring intermediate nodes if the destination node is out of range of the source node.

As a result, ad hoc networks enable the instant deployment of communication networks without pre-existing infrastructure or centralized management. The formation of the network is done dynamically, the set of management tasks being distributed among all the nodes of the network.

The main characteristic of ad hoc networks is that the nodes belonging to this network play, or can play, the role of routers. The nodes are therefore themselves responsible for establishing and maintaining network connectivity in a continuous manner. This is achieved through the use of specific routing protocols that allow the nodes to exchange routing information between neighboring nodes and calculate communication paths to all other nodes in the network. These routing protocols issue messages periodically to update the topology of the ad hoc network (i.e. to identify nodes and links between nodes).

There are two families of routing protocols: proactive protocols and reactive protocols. For the family of proactive protocols, each node has a vision over the entire network through a periodic exchange of routing tables. All paths are available directly through the routing table.

For the reactive protocol family, paths are only available on demand. Indeed, if a path to a destination is not available via the routing table, it launches a path search request, the result of this query to retrieve a path, if there is one.

In the context of the present invention, it is more particularly interested in proactive routing protocols including the OLSR protocol (Optimized Link State Routing).

Figure 1 shows the components of the OLSR proactive routing protocol. In this protocol, two main components can be distinguished: a maintenance component of the topology 10 comprising a topology control module 11 in conjunction with a routing node selection module 12 and a path selection component 20 comprising a module or path calculation algorithm 21. The maintenance component of the topology 10 ensures, through a periodic exchange of control messages, the construction of the topology graph of the network which will subsequently be used for calculating the paths. This mechanism also minimizes the overhead in network traffic by using a mechanism for selecting the router nodes, called Multipoint Relay Nodes (MPRs).

The path selection component 20 calculates, based on the information collected on the topology, the best routes between the nodes of the network using a path calculation algorithm on a graph (for example: Dijkstra algorithm), the criterion of choice. paths being the number of jumps.

Ad-hoc proactive routing protocols have been designed with no explicit consideration of QoS for path computation. The number of jumps is generally the criterion adopted by these protocols. It is clear that such a criterion is inadequate for real-time applications such as videoconferencing or telephony.

The consideration of the quality of service in the routing protocol passes through the predefinition, at the time of its design, at the level of the path selection process, new criteria, called quality of service metrics. In this case, as illustrated in FIG. 1, the path selection component 20 also comprises a quality of service metrics management module 22 associated with the path calculation algorithm. metrics are the metrics of delay, bandwidth, jitter, etc. Information about QoS metrics is injected into the topology graph. A new graph enriched by this quality of service information is therefore reconstructed and the computation of the paths is done taking these metrics into account.

According to the known art, the decision concerning the choice of quality of service metrics, which serves as a criterion for selecting paths, is programmed statically. As a result, it is impossible to change these criteria once the routing protocol is implemented.

We also observe that the known solutions recommend the use of a single metric or a combination of predefined metrics for the sake of optimization for a given case (bandwidth or delay, reliability, energy, etc.). However, we quickly notice the limitations that result from such static management of these metrics. Indeed, when one or more applications running in an ad hoc network are used together with a route determination based on a routing algorithm using an inadequate metric, the quality of service rendered to these applications is not the same. better. This is all the more true as the constraints of applications in terms of quality metrics are generally different from each other.

In order to overcome these limitations, one solution is to implement a selection of multi-metric (or multi-criteria) paths, which implies the definition of an algorithm capable of finding the best paths for all the possible metrics. However, to implement such an algorithm is impossible and corresponds to the situation called "NP-Complete problem" in theory of the complexity of the problems of decision in computer science (a problem is said NP-Complete if it is in the class of the problems of decision for which the answer yes can be decided by a non-deterministic algorithm in a polynomial time by relative to the size of the instance, and if any NP-Complete problem can be rewritten using a polynomial algorithm as an instance subset of this problem). Calculation approximation techniques (based on heuristics) exist, but they are limited to a predefined number of metrics and their implementation is otherwise static. Consequently, the same limitations as those mentioned in the first situation will be present.

Object and brief description of the invention

The present invention aims to remedy the aforementioned drawbacks and to propose a technical solution for adapting a particularly proactive routing protocol (such as OLSR) so as to allow a dynamic change and implementation of the quality of service metrics used to the calculation of paths in ad hoc networks, taking into account the characteristics of the network and / or the resources required for the applications used.

This goal is achieved through a method of dynamically adapting the quality of service metric that includes the following steps: a) determining at least one quality of service metric to be applied at a given time based on the quality of service available on the network and / or on the quality of service required by one or more applications, b) transmitting to at least a portion of the network nodes of the instantaneous quality of service metrics to be applied, which includes the calculation modules and inserting quality of service metrics at the routing protocol control packet level, and c) updating the node routing table based on the instantaneous quality of service quality metrics to be applied received.

Thus, this method makes it possible to dynamically apply, at the level of the routing protocol, the quality of service metric that best corresponds at the same time to the constraints of the environment (number of nodes, density, degree of mobility, etc.) and / or the state of the network (available resources and / or running applications). By dynamically applying the most relevant quality of service metrics at a given time, the implementation of the mechanisms described in the present invention makes it possible to respond effectively to the inherently dynamic behavior of the ad hoc networks.

For this purpose, in step a), two alternatives are possible. In the first, each node analyzes the exchanges with its neighbors and decides by itself the choice of metrics, in the manner of self-organized networks. In the second, a network manager is used which supervises the state of the resources of each node and / or the resources requested by the current applications on the network. It decides and implements the necessary modules for the management of adequate quality of service metrics.

In step b), the quality of service metrics to be applied are inserted into control messages of the routing protocol. In this way, any new quality of service metrics to be applied is propagated in the network via generic control messages, the data relating to this metric being extracted at each node through a metric manager. This avoids having to rewrite the routing protocol at each change in quality of service metrics.

In step c), the computation of the path and the update of the routing table according to the quality of service metrics received can be done directly from the routing protocol calculation module or from the routing protocol module. a path calculation module external to the protocol. In the latter case, the method further comprises a dynamic deployment step, for example by downloading, a path calculation module. The module is then said to be re-programmable.

The steps of the method described above are executed by a computing device, in this case at least one node of the network, under the control of software instructions. Therefore, the invention also relates to a computer program or software module for storage in or transmitted by a data carrier comprising software instructions for executing the method by a computing device. The data carrier may be a hardware storage medium, for example a CD-ROM, a magnetic diskette or a hard disk, or a transmissible medium such as an electrical signal, optical or radio.

The invention also relates to a system for dynamic management of the quality of service metric in an ad hoc network, the system comprising a plurality of nodes for forming a routing infrastructure for the routing of data packets, characterized in that it further comprises a network manager for determining the quality of service metrics to be applied at a given time based on the quality of service available on the network and the quality of service requested by one or more applications, and means to broadcast the quality of service metric to be applied to the nodes of the network and that each node includes a metrics manager for updating the routing table of the nodes according to the quality of service quality metric to be applied received.

Thus, the system of the invention comprises means to ensure the supervision (monitoring) of the network to have at all times a consistent view of its state, namely the rate of available resources and the resources required by applications that are running. From this data, the quality of service metric to be applied is determined and deployed at the routing protocol level through a periodic exchange of information concerning quality of service metrics between the nodes of the network. This periodic exchange is achieved by means of control messages of the routing protocol in which the metric to be taken into account.

The network manager can be integrated with one or more nodes of the network, or be implemented in a specific mobile or wired terminal having a connection to the network.

The computation of the routes at the nodes according to the broadcast quality of service metrics can be carried out by the path calculation module specific to the routing protocol or be managed externally by a re-programmable external module for calculating the routing. shared path between several applications with the same quality of service requirements or outsourced in applications so that each application can select the most relevant paths vis-à-vis its quality of service constraints. The subject of the invention is also a mobile or fixed terminal intended to form a node in an ad hoc network, characterized in that it comprises a metric manager for updating the routing table of said node as a function of a metric instant quality of service to apply. Such a terminal may also comprise means for periodically taking into account any change in quality of service metrics determined as a function of events occurring in the network and at the level of the applications.

Brief description of the drawings

Other features and advantages of the invention will include the following description of particular embodiments of the invention, given by way of non-limiting examples, with reference to the accompanying drawings, in which:

FIG. 1 schematically represents the components of the OLSR proactive routing protocol;

FIG. 2 represents an embodiment of an architecture according to the invention;

FIG. 3 illustrates an example of an ad hoc network topology used to test the method of the invention;

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

The present invention is intended to allow the extemalization of the management of quality of service metrics to the routing protocol in an ad hoc network and, moreover, the determination, the diffusion and the taking into account of any type of quality of service metrics. . For this purpose, the invention proposes a technical solution that implements two main components, one at the network level (network manager) and the other at the node level (metric manager), as well as an extension of the Routing protocol control packets.

The invention uses and adapts (ie addition of extension) a proactive routing protocol and in particular one of the most well-known proactive routing protocols; the OLSR protocol. This protocol is notably referenced and described under the name OLSR RFC3626 (Request for Comments) (see in particular the "Optimized Link State Routing Protocol (OLSR)", Network Working Group, T. Clausen et al., October 2003) of the Manet Working Group (for Mobile Ad hoc Networks) of the Internet Engineering Task Force (FIET).

To enable the deployment and application of any type of quality of service metrics at the routing protocol level without having to redefine the protocol at each metric change, the present invention proposes to reuse the existing messages of the routing protocol and not to define new messages. The messages used are preferably messages exchanged periodically between the nodes of the network such as the Topology Control (TC) control messages in the OLSR protocol. However, new messages can also be used for transporting quality of service metrics.

Thus, in accordance with the invention, generic control messages are used to carry any quality of service metrics as well as a processing function which constructs at each node a graph on the network topology; each element of the graph is represented by an n-tuplet of the form <source-address, destination-addresses, metric, metric2, ..., metric N>. This topology will be used later by the route calculation. Broadcasting any quality of service metrics to network nodes is done through such messages.

At each node, a metric manager specific to the invention is connected to the routing protocol. More specifically, as illustrated in FIG. 2, a node 100 comprises a first layer 110 which, in a known manner, corresponds to the layer of the routing protocol 110 which notably uses a routing table 1121 and a path calculation module or algorithm 1122. The routing table 1121 is maintained (ie updated) locally in each node using the path calculation module 1122. It is the routing table that gives the address of the neighboring node to which it must be transmitted. the packets or the frame so that they reach their destination according to the defined quality of service metrics. According to the invention, a metric manager 111 is added to the layer 110 which transmits the metric (or the combination of metrics) to be applied to the network to the routing protocol 112. The path calculation is then carried out from this metric using a path search algorithm in a graph, such as, for example, the Dijkstra algorithm where the values (or weights) associated with the edges are then given by the values of the metrics selected.

The metric manager is a component distributed to all nodes of the network. It implements, at the node level, the quality of service metric chosen by the network manager. For this purpose, the metric manager installs into a layer 120 the components 121 necessary for the insertion of the quality of service metric in the path calculation process. The metric manager 111 also makes it possible to indicate the existence of the external computation modules of path 131 to the routing protocol 112. The routing protocol can thus transfer to the external modules of path calculation a topological view of the network containing the metrics on which will carry the specific path calculation to the plugin.

This transfer can be done directly or via a specific component as described in detail in the patent application filed under the number FR 03 12869 and entitled "Method of notification of changes in the state of resources of a network destined to less an application, computer program and state change notification system for the implementation of the method ". Two modes are possible however:

- the push mode: The routing protocol periodically sends a topology view to the modules concerned.

- the pull mode: only at the initiative of the interested modules for the routing protocol to transfer the topology data to them.

These quality of service metrics components, which can be dynamically deployed or deployed on each node as it enters the network, are used by the metrics manager to adapt the value of the instantaneous metric for the direct neighborhood. Furthermore, the system of the invention comprises means for determining the quality of service metric (s) that must be taken into account by the nodes for the routing. The network manager 200 is an entity that can be integrated with one or more nodes of the network, or be implemented in a specific mobile or wired terminal having a connection to the network.

As illustrated in FIG. 2, a network manager 200 includes a quality of service metrics determination module 210 in connection with a supervision module 220 whose function is to supervise the state of the resources of the network vis-à-vis events that occur (disappearance / occurrence node, decrease / increase bandwidth capacity, power, etc.) and resources required by current applications. To do this, any new application must register with the network manager with its QoS requirement (eg an IP voice application registers with a maximum delay of 250 msec). The manager thus has a vision on all the application requirements. The information concerning the state of the network resources is reported to the module 220 through probes installed at each node (i.e. each user terminal). An information exchange rule base can be defined at the supervision module level to enable it to process the events being reported.

The determination module 210 integrates the decision logic of the metric to be applied in the network according to the state of the resources of the network and / or the requirements of the applications indicated by the supervision module 220. Indeed, on receipt of a new notification of the supervision module, the determination module is invoked, and quality of service metrics to be deployed will be determined.

The QoS metrics decision, once taken, will be communicated by the network manager to the metrics managers of all nodes in the network for implementation. However, an exchange protocol ensuring the transmission of configuration orders from the network manager to the metric manager is defined. This exchange is done through mechanisms of reliable and atomic transmission. This protocol includes the following functions:

- DeployerMetriqueQoS (metric): it makes it possible to deploy a quality of service (QoS) metrics given on the network, namely the modules of calculation and insertion at the level of the control packets.

- DeleteMetriqueQoS (metric): the invocation of this function makes it possible to no longer consider the metric in question.

- DeployerPath (module): allows to implement an external path calculation module

- DeletePath (Module): Disables a path calculation module previously implemented.

In order not to affect the good functioning of the network, considering that an ad hoc network is a network with variable resources in time, tolerance thresholds can be fixed at the level of the nodes of the network (minimum energy level, level maximum charge, etc.).

According to an alternative embodiment, it is possible to have an external management of the routing process via a path calculation module 131 which is deployed dynamically in a layer 130. In this case, the existing routing protocol 112 uses the module path calculation 131 instead of its internal module 1122. The routing protocol 112 transmits to the module 131 the topology graph enriched by the quality of service information provided by the metrics calculation module 132 at each node. Applications must be modified to take into account this new module, which can be either specific to each application or shared by several applications. In the second case, the module is transparent to the application since the result of the calculation of metrics is reinjected into the routing protocol with which the application communicates. In both cases, this new route calculation does not impose or very little modification on the initial routing protocol. In addition, this plug-in is re-programmable at any time, which allows it to integrate new metrics dynamically on initiative of the metrics manager. External management of service quality and calculation metrics is achieved. path. This makes it possible to manage the routing topology with QoS metrics at the application level so that they can apply the most optimal path calculation to their service quality requirements.

In what follows, the interactions between the components of FIG. 2 are first described by a fictitious example. A second example is then described which illustrates a possible implementation of the present invention.

Description of the interactions:

For example, consider a spontaneous ad hoc network forming in an area devoid of infrastructure. By default, the topology discovery protocol included in the routing protocol 130 does not include any specific quality of service metrics. When a node in the network is requested by a Voice over IP (VoIP) application that requires constant bit rate (CBR) traffic characteristics, a new metric must be exchanged between the nodes and a specific path calculation based on this metric set up to define an optimized path for the VoIP application. A first step is to choose the metric available in the network that is closest to that expected by the application. This can be for example jitter, delay or default the number of jumps. This decision may be local to the node that will propagate it to the other nodes (according to the well-known approach of "self-organized" networks) or global by the network manager 200 which will transmit it to the nodes via a control message specific as previously described. The external computation module 131 associated with the chosen metric, for example the delay, is then activated on each node or possibly deployed dynamically from the network manager. The chosen metric, here the delay, is then also added in the control messages exchanged between the nodes by the routing protocol to discover and maintain the topology. When the VoIP application tries to establish a call, it invokes the external path computation module specific to the chosen metric, in this case the delay. This module can be present on all nodes or dynamically deployed. This module retrieves from the routing protocol the topology graph having the delay metric (the metric information is computed by the metric calculation module at each node and carried by the routing protocol control packets) . In addition, the other applications use the default path calculation module, namely the number of jumps. The VoIP application then has routes adapted to its delay constraint, while other applications have paths that may be shorter but may also be more loaded. This is not a problem for example for a data exchange application.

Example of implementation:

A particular example of implementation of the invention is described in connection with FIG. 3 which presents an example of an ad hoc network topology with a configuration that makes it possible to show the limitations of the current solutions based on fixed metrics and the advantages of the invention in terms of dynamic adaptation to changes in quality of service conditions in the network environment (network state and applications). The network illustrated in FIG. 3 comprises seven nodes formed by seven terminals of two types: three high-capacity terminals (PC computers) Tm, T _H2 and T _H3 , on the one hand, forming a first route R1 and on the other hand , four terminals with low capacity (PDA assistant) Ts, TFi, TF ₂ , T _D , terminals TFi and TF ₂ forming a second route R2 between a source node and a destination node respectively formed by the terminals T _s and T ₀ .

All nodes use 802.11b wireless interfaces with a bit rate of 11 Mb / s. The Rl route is made up of three PCs, which promotes better routing if the "delay" metric is used while the R2 route consisting of two PDAs helps a routing based on the "bandwidth" metric.

In this particular example, we consider two applications involving two different types of traffic, each with different requirements: the first application runs on TCP (Transfer Control Protocol) and requires bandwidth (eg file transfer, http, etc.). ), the second on UDP (User Datagram Protocol), rather real time, and which favors the delay (eg multimedia transmission).

The "failover" rules of the metrics for this test network are furthermore defined according to the following algorithm:

beginning

If (Event = Alteration of the resources nodes_low_capacities) then metric = Nodes reliable.

Otherwise (other events)

If (no conflict between applications) then metric = default metric of applications. / * same metric for all applications * /

If not metric = delay. / * preferred metric * / End.

This data makes it possible to choose the metric to be applied in the network according to the rules defined in the network manager. Depending on the decision, the data will be routed either via route Rl (metric delay) or route R2 (metric bandwidth).

The following table shows the behavior of the approach according to the invention. Specifically, it describes the metrics to be applied in the network based on events that arise in the network.

In view of these results, it is clear that the choice of the metric applied in the ad hoc network has a paramount influence on the quality of service provided to the application, according to these requirements.

At the level of the results, we note that the application of the bandwidth metric makes it possible to obtain good performance at the bandwidth level, to the detriment of the delay which increases very significantly. This is advantageous for applications that require significant bandwidth, however time-sensitive applications are heavily penalized. One can observe the complementary phenomenon for the delay metric: the delay is lower but the bandwidth is lower than that obtained with the metric of the bandwidth.

Nevertheless, innovation provides the best compromise to apply the instant metric that best meets the needs of applications given the constraints of the environment.

The results obtained on this example demonstrate the efficiency of a dynamic management of the quality of service metric. Unlike a rigid, fixed-metric approach, this dynamic QoS metrics management provides enough flexibility to best meet the QoS policies defined in the network.

Claims

A method of dynamically adapting the quality of service metric for routing in an ad hoc network comprising a plurality of routing nodes (100) for optimal routing of data packets between these nodes according to the network topology to a given instant, said method comprising the following steps: a) determining at least one quality of service metric to be applied at a given instant based on the quality of service available on the network and / or on the quality of service requested by a or more than one application, b) transmission to at least a portion of the network nodes of the quality of service metric to be applied, c) updating of the routing table (1121) of the nodes according to the instantaneous quality metric of service to be applied received.

Method according to claim 1, characterized in that, in step a), a re-programmable network manager (200) supervises the state of the resources of each node (100) on the basis of the quality metrics. applicable at any given time, as well as the resources requested by the applications running on the network.

3. Method according to claim 1 or 2, characterized in that, in step b), the quality of service metric to be applied is inserted into control messages of the routing protocol.

4. Method according to one of claims 1 to 3, characterized in that it further comprises a step of external management quality of service metrics and path calculation by modules managed by a given application or modules re-programmable (131) shared by several applications.

A computer program comprising instructions for performing the method according to one of claims 1 to 4.

Recording medium on which the program according to claim 5 is stored.

A system for dynamic management of the quality of service metrics in an ad hoc network, the system comprising a plurality of routing nodes (100) for routing data packets, characterized in that it further comprises a network manager (200) for determining and calculating a quality of service metric to be applied at a given instant based on the quality of service available on the network and the quality of service requested by one or more applications and means for broadcasting the metric the quality of service to be applied to the nodes of the network and that each node includes a metrics manager (111) for updating the routing table (1121) of the nodes according to the quality of service quality metric to be applied received.

8. System according to claim 7, characterized in that the network manager comprises means (220) for monitoring the state of the resources of each node and the resources requested by the current applications on the network.

9. System according to claim 7 or 8, characterized in that it comprises means for calculating and inserting the quality of service metric in control messages of the routing protocol.

10. System according to any one of claims 7 to 9, characterized in that the network manager (200) is integrated with at least one node of the network or in that the system further comprises a mobile or wired terminal connected to the network and integrating the network manager.

11. System according to any one of claims 7 to 10, characterized in that it further comprises means for transmitting to the network nodes re-programmable software modules for calculating path and quality of service metric management (131, 132).

System according to any one of claims 7 to 10, characterized in that it further comprises means for managing the routing topology with quality of service metrics at the application level so that they can apply the most optimal path calculation with respect to their need for quality of service.

13. Mobile or fixed terminal intended to form a node (100) in an ad hoc network, characterized in that it comprises a metric manager (111) for updating the routing table (1121) of said node as a function of a quality of service metric transmitted in the network.