WO2012042431A1

WO2012042431A1 - Node configuration mechanism for improving mesh scalability

Info

Publication number: WO2012042431A1
Application number: PCT/IB2011/054110
Authority: WO
Inventors: Theodorus Jacobus Johannes Denteneer
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-09-27
Filing date: 2011-09-20
Publication date: 2012-04-05
Also published as: TW201218810A

Abstract

The present invention relates to a method and apparatus for reconfiguring nodes of a wireless mesh network as either beaconing and participating in the formation of the mesh (mesh or AP mode) or as non-beaconing and not participating in the mesh formation (STA mode). The invention leverages the ability of modern implementations to map several wireless entities on one wireless card. Thus, it is possible to reconfigure nodes 10 without changing the hardware.

Description

NODE CONFIGURATION MECHANISM FOR IMPROVING MESH SCALABILITY

FIELD OF THE INVENTION

The present invention generally relates to an apparatus and method for configuring a network node of a wireless mesh network. BACKGROUND OF THE INVENTION

Starting from the first 802.11 standard of the Institute of Electrical and Electronics Engineers (IEEE), ad hoc networking has been specified in the independent basic service set (IBSS) mode. In this mode, stations (STAs) can connect to each other without any central coordinator like access point (AP). Moreover, there is no access or connection to the distributed system (DS). Thus, STAs are totally self-contained as an ad hoc network.

Wireless mesh networks use multi-hop routes to establish communication between the nodes in the network as well as to applications residing in the Internet. Thus, they avoid the use of costly, wired infrastructure. However, this technology still presents many challenges as both theoretical research and practical applications show that the current technology does not scale well. Therefore, the size of the meshes (in terms of number of nodes per wired gateway to the internet) remains limited and this hampers their economic feasibility.

Current standard developments that target mesh networks acknowledge this limitation of the current technology. E.g., the current mesh standardization in the IEEE (IEEE 802.11 TG s) targets a mesh size of only 32 mesh STAs, reflecting the perceived lack of scalability of mesh networks based on WiFi (Wireless Fidelity) technology.

There are currently two ways to implement mesh networks using WiFi technology: being layer-2 and layer-3 mesh networks. Here the number refers to the layer in the OSI stack, where layer 2 is the Media Access Control (MAC) layer, and layer 3 is the networking layer. In layer-2 mesh networks, routing takes place at the MAC layer. Thus, in such mesh networks, all nodes are involved in beaconing and routing. E.g. IEEE 802.11 TG s standardizes mesh networks that operate at MAC layer (layer 2).

Fig. 2 shows a schematic example of a layer-3 mesh network with nodes A to F. In such layer-3 mesh networks, routing is performed at the network layer. In this case the MAC layer serves to connect the nodes in the network that are in range of each other. A common method to implement such a layer-3 mesh network, is by using regular IEEE802.11 APs and non-AP STAs. In this case, each node includes an AP entity as well as one or more STA entities. A STA entity in the node can connect to the AP entity in a neighbour node. If a node needs to connect to multiple neighbours, it will include various STA entities, as a STA entity can associate with one AP only, according to the standardized IEEEE 802.11 protocol.

One of the main causes of this lack of scalability is the amount of broadcast messages needed to operate the mesh. E.g., in wireless mesh networks as proposed in IEEE 802.11 TG s, each mesh STA (i.e. node in the mesh network) beacons. Thus each node transmits beacons at 100 ms interval. These beacons are coded conservatively and send at low coding and modulation rates so that they take long to transmit and have a large reception range. Even if the beacon size is just around 100B, together with preambles and intra frame spacings (beacons use PIFS (Point Coordination Function (PCF) Interframe Space) access) it can still take up to 1ms to transmit the beacon, e.g. assuming that the beacon is transmitted at IMbs. Therefore, the beacons generated in a mesh network with substantial mesh node density will occupy much of the air time. This will dramatically reduce the amount of air time available for regular data traffic for which the mesh is intended.

E.g., it is not unrealistic to expect a mesh node in a dense mesh network to

"see" 25 neighbours. Typically, each of the nodes broadcasts beacons at a 100ms rate. Thus, only accounting for the beacons more than 25% of the air time is already in use for beacon frames to manage the network.

An additional source of traffic is due to the routing protocols. E.g. in route discovery protocols, mesh STAs broadcast route requests with the address of a target mesh node in order to discover a route to other nodes. These route requests are re-broadcast until the target node receives the packet. The target node replies via a unicast transmission, which means that the reply message is sent to a single network destination (i.e., the requesting mesh STA) identified by a unique address.

As an alternative, the mesh is equipped with a root node via which all packets are relayed. So in order to transmit a packet to a communication partner, a node sends the packet to the root node which then relays the packet to the communication partner. For this mechanism to be functional, every node must know a route to the root node, and the root node must know the route to every node in the mesh network. This is again achieved via broadcast messages. The root broadcasts a root announcement, which is then relayed via a broadcast by the nodes that receive this announcement. So that eventually all nodes in the mesh are reached. By storing the node from which the "most favourable" root announcement was received, this mechanism informs each node of a route to the root node. Nodes can reply with unicast messages to the root node via the discovered route, so that they can announce their existence in the mesh to the root node.

In some protocols, such as the IEEE 802.11 TGs, these reactive route discovery mechanisms co-exist with the proactive root announcement. Thus, each node always has a route available which can then be refined as deemed necessary. As nodes in a mesh are mobile and because the transmission medium is variable, such route discovery procedures must be repeated at some time intervals to keep the routes up to date so that nodes remain reachable. All nodes that form the mesh will be involved in these route discovery procedures and use the Wireless Medium to broadcast the control packets that are needed by the routing protocol. This again limits the amount of bandwidth available for useful data packets considerably.

Thus, excessive beaconing and broadcast traffic in mesh networks consume considerable amounts of air time and bandwidth, so that useful throughput is considerably reduced. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a flexible mechanism to improve scalability of wireless mesh networks.

This object is achieved by an apparatus according to claim 1, a method according to claim 9 and a computer program product according to claim 10.

Accordingly, the number of mesh nodes that beacon and that participate in the route discovery can be reduced, as it is possible to reconfigure network nodes via configuration control mechanisms (which may be software or hardware implemented) without changing the hardware of the network nodes. This dramatically reduces the amount of airtime used up by broadcast traffic and allows much higher useful data throughput in the mesh. In particular, it is possible to reconfigure the network nodes as either beaconing and participating in the formation of the mesh (mesh or AP mode) or as non-beaconing and not participating in the mesh formation (STA mode). Thus, the above problem is mitigated by building on top of current standards and implementations. According to a first aspect, the network node may be initially set (e.g. by the node configurator or a node configuration function) into the relaying operation mode so as to build and advertise neighborhood information deduced from observed beacons of neighboring nodes. Thus, each newly initialized network node can obtain up-to-date information about its current neighborhood.

According to a second aspect which can be combined with the above first aspect, the initial relaying operation mode may be maintained (e.g. by the node configurator or a node configuration function) until no changes have been observed in the neighborhood information for a predetermined period of time. This ensures that neighboring nodes share the same neighborhood information.

According to a third aspect which can be combined with any one of the above first and second aspects, the subset of nodes may be selected (e.g. by the node selector or a node selection function) based on the neighborhood information and an additional seniority information collected from neighboring nodes, the seniority information indicating a node with the highest address in a neighbor list. Thereby, some additional intermediary information can be included in the selection process.

According to a fourth aspect which can be combined with any one of the above first and third aspects an access point interface and either a mesh interface or at least one station interface may be set up (e.g. by the node configurator or the node configuration function), if the network node belongs to the selected subset, and a station interface may be set up only, if the network node does not belong to the selected subset. Thus, several wireless entities can be mapped on one node.

The apparatus may be implemented as a chip module, chip set, circuit or software-controlled processor, and may be provided in a network node (i.e. wireless node) or in a station management entity for the wireless mesh network.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following drawings:

Fig. 1 shows a schematic block diagram of a configuration control apparatus according to a first embodiment;

Fig. 2 shows a schematic example of an architecture of a layer-3 mesh network; and Fig. 3 shows a flow chart illustrating an exemplary configuration control method according to a second embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

According to the following embodiments, a wireless mesh network architecture can be provided, where each wireless node can run a distributed selection algorithm so that a subset of the nodes is selected to become relaying nodes (e.g. AP nodes). The remainder of the nodes become non-relaying nodes (e.g. STA nodes). Possible selection algorithms have been studied, with the algorithm described in Baker and Ephremides, "The architectural organization of a mobile radio network via a distributed algorithm", IEEE Trans. Comm. Vol 28, no 11, pp. 1694-1701, 1981 giving one possible option.

Fig. 1 shows a schematic block diagram of a wireless node 10 with a configuration functionality which may be implemented as a hardware circuit or as a software routine which controls a processor responsible for node configuration. An operation processor (OP) 104 is adapted to control the operation of the wireless node or several wireless interfaces thereof to enable, among others, beaconing and route discovery. To achieve this, the operation processor 104 controls a beacon generator (BG) or beacon generation functionality 106 to supply beacon information to a radio unit 108 with a transceiver for broadcasting the beacon information via an antenna. Additionally, the operation processor 104 receives and transmits routing information via a route discovery unit or functionality (RD) 107. In Fig. 1, the beacon generation functionality 106, the route discovery unit 107 and optionally the operation processor 104 are shown in a dashed box which indicates a wireless entity controlled by the node configurator 102. It is noted that the wireless node 10 may comprise a plurality of such wireless entities to obtain a plurality of wireless interfaces. As an alternative, a single operation processor 104 may be provided, which is adapted to control a plurality of wireless entities. Based on the selected configuration, wireless entities (interfaces) or their functionality can be activated or deactivated.

A detailed description of the beaconing and route discovery operations is omitted here for brevity reasons. These operations may correspond to the standard operations defined in the corresponding IEEE 802.11 protocols.

Additionally, according to the embodiments, a node configurator or node configuration functionality (NC) 102 is provided, which is responsible for selecting a node configuration of the wireless node 10 or the wireless interfaces thereof and for supplying corresponding control information which indicates the selected configuration to the operation processor 104. Additionally, the node configurator 102 supplies beacon control information to the beacon generator 106 and receives advertised beacon information throught the radio unit 108 from other wireless nodes.

As an alternative, the functionality of the node configurator 102 may be provided or integrated as an additional functionality or routine of the operation processor 104. E.g., the node configurator 102 and the operating processor 104 could be implemented by a software-controlled central processing unit (CPU) and lower MAC processing and radio unit 108 could be implemented on a radio chip.

More specifically, the node configurator 102 comprises at least a neighbour detection unit or functionality 1021 which is adapted to control the beacon generator 106 to advertise neighbourhood information (e.g. a neighborhood list) and to store received neighbourhood information. Additionally, the node configurator 102 comprises a relay node selector or selection function (RS) 1022 for selecting a subset of wireless nodes of the wireless network at least based on the stored neighbourhood information.

To enable the selection procedure, the neighbour detection unit 1021 of the wireless node 10 includes in a first phase of the selection algorithm in its beacons the neighbourhood information, e.g. a list of its neighbour nodes, as can be deduced from observed beacons received via the radio unit 108. These neighbours can be uniquely identified by the MAC address of the beaconing node. From the received beacon, each node can derive the set of neighbours for each of its neighbours. The neighbour detection unit 1021 of the wireless node 10 may continue to built and beacon this neighbourhood information until it does not observe any changes for a predefined period of time. To transmit this information, the nodes may use a predetermined information element specifically designed for this purpose. Modern open source implementations allow the beacons to carry such information elements that must not be defined in the standard.

This first phase of the selection process could be followed by a second phase of the algorithm, in which the relay node selector 1022 of the wireless node 10 also includes some intermediary information on the selection process. E.g., if the algorithm by Baker and Ephremides is followed, the relay node selector 1022 controls the beacon generator 106 to additionally include in its beacons whether they are seniors, i.e. have the highest identifying address in their own neighbour list or in the neighbour list of any of their own neighbours. This identifying address can be based on the MAC address of a node, but can also be based on another characteristic or be a randomly generated number of sufficient length. Alternatively, each node can be controlled to broadcast its own senior, along with a list of seniors for each of its neighbouring nodes. Based on this information, the relay node selector 1022 can then complete the implemented relay node selection process or algorithm. After the two phases of the above node subset selection algorithm, the node configurator 102 reconfigures the wireless node 10, if the relay node selector 1022 has selected the node 10 itself as relay node (e.g. as a AP-STA combo node), whereas a node that has not selected itself as a relay node will reconfigure itself as a STA node only. A node that is configured as an AP-STA combo established an AP interface as well as several STA interfaces and a STA node will only establish a STA interface. As only the AP interface is involved in beaconing and route discovery, only a subset of the nodes is involved in beaconing and route selection.

Alternatively, using the IEEE 802.11s amendment, nodes selected as relay nodes are configured to establish a mesh interface and an AP interface, whereas the nodes selected as non-relay nodes are configured to establish a STA interface, with similar advantages as above, but now being able to leverage the improvements brought by the IEEE 802.11s mesh amendments. The nodes that establish the STA interface only can still be reached within the mesh network by using a proxy protocol defined in the mesh standard.

The node configurator 102 may thus bring (multiple) wireless entities (i.e. dashed box in Fig. 1) up and down, and communicate with them. Each of these wireless entities may then communicate via one (and the same) radio unit 108. These entities may differ among themselves with respect to beaconing and routing (as well as some other optional details which are omitted here and not necessary to understand the present invention). It is therefore noted that Fig. 2 is a simplified block diagram, as the node configurator 102 may control several beaconing and route discovery functionalities or unities and also other node functionalities - not only beaconing and route discovery.

Fig. 3 shows a flow diagram of a selection procedure according to a second embodiment, which is executed by the wireless nodes participating in the mesh formation.

In an initial step SI 00, the node is configured as an AP and may thus beacon its neighbourhood information in step S101, which includes a list of neighbours and neighbour neighbours. In step SI 02, it is checked at the node, whether the transmitted and received beacons converge in their neighbourhood information. If not, the beaconing in step S101 is continued until convergence is detected. If the neighbourhood information is determined to converge in step SI 04, it is checked in step SI 05 whether the node itself has been selected as relay node, i.e., belongs to the selected subset of relay nodes. If so, the node is configured in step SI 06 as relay node (e.g. AP-STA combo) and can now operate in step SI 07 as AP-STA combo which issues beacons and performs route discovery. In step S 108 it is checked whether a start-up or reconfiguration operation of the node is required. If not, the procedure continues with step SI 07. Otherwise, if start up or reconfiguration is determined in step SI 08, the procedure jumps back to step SI 00 and starts again.

If it is determined in step SI 05 that the node has not been selected as relay node, the node is configured in step SI 09 as simple STA node and now operates in step SI 10 as simple STA no which does not issue any beacons and does not perform any route discovery. In step Si l l it is checked whether a start-up or reconfiguration operation of the node is required. If not, the procedure continues with step SI 10. Otherwise, if start up or reconfiguration is determined in step S 111 , the procedure jumps back to step S 100 and starts again.

The above described procedure may be implemented as a software routine. The steps may be performed by software code portions of a computer program product for a computer when the product is run on the computer.

The proposed embodiments can be implemented on an operation system platform (e.g. Linux platforms) and thus leverages the ability of such implementations to map several wireless entities on one wireless card. Moreover, it utilizes the ability of such implementations to bring up and down the run time of such interfaces. Thus, it is possible to reconfigure nodes via software operations without changing the hardware. In particular, it is possible to reconfigure the nodes as either beaconing and participating in the formation of the mesh (mesh or AP mode) or as non-beaconing and not participating in the mesh formation (STA mode).

As a third embodiment, it is also possible to include these operations within the standard. For this, the standard already provides the functionality to bring up and bring down various wireless entities. However, the station management entity (SME) cannot currently derive from the MAC layer Management Entity (MLME) the information to run an algorithm that selects nodes as either forming the mesh (i.e. beaconing and participating in the route establishment) or being proxied by the mesh (i.e. not beaconing and not participating in the route establishment).

To enable this, some information elements can be defined, that allow the wireless nodes to derive the needed data structures to run a subset selection algorithm. E.g., the information element to be used in the first phase of the selection algorithm could be a list of neighbours, and the information element to be used in the second phase of the selection algorithm could be some senior information, as indicated above. The information can then be utilized by the MAC layer. In a specific example, the information may be passed via an MLME-SME interface to the SME e.g. providing the SME with a list of neighbours and, for each neighbour, its senior and a list of its neighbours. In this case, the node configurator of Fig. 1 is provided at the SME.

In summary, a method and apparatus have been described for reconfiguring nodes of a wireless mesh network as either beaconing and participating in the formation of the mesh (mesh or AP mode) or as non-beaconing and not participating in the mesh formation (STA mode). The invention leverages the ability of modern implementations to map several wireless entities on one wireless card. Thus, it is possible to reconfigure nodes without changing the hardware.

The above embodiments can be based on the IEEE 802.11 standard and can be implemented without changes to the currently available IEEE standard. Also, the proposed selection and configuration procedure can be used in conjunction with the forthcoming IEEE 802.1 Is amendment to this standard, without altering this amendment.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments and can be used for all kinds of ad hoc networks or wireless mesh networks. Such mesh networks may include outdoor mesh networks for example, where lamp poles contain radio nodes that interconnect to form a mesh for lamp management. For this application, little bandwidth is needed and 802.11 technology appears to be too heavy and expensive, and cheaper IEEE 15.4 technology can be used. However, in more future outdoor scenarios, more bandwidth intensive applications could be envisaged, e.g. as flexible means to deploy security cameras, or run a variety of other services over the network. One can also imagine these outdoor meshes to be part of the connectivity infrastructure to support the smart grid, or enable the lamp poles to become themselves part of the smart grid. The above embodiments enable such outdoor mesh networks. They provide a building block to design such outdoor meshes with scalability that considerably improves upon the current state of the art.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality of elements or steps. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

1. An apparatus comprising:

a node configurator (102) for selectively setting said network node (10) into a relaying operation mode, in which said network node (10) is controlled to beacon and participate in a formation of said mesh network, and into a non-relaying operation mode, in which said network node (10) is controlled not to beacon and not to participate in the formation of said mesh network; and

a node selector (1022) for selecting a subset of nodes of said mesh network as relaying nodes based on a neighborhood information collected from neighboring nodes;

wherein said node configurator (102) is adapted to set said network node (10) into said relaying operation mode if said network node (10) belongs to said subset of nodes and into said non-relaying operation mode if said network node (10) does not belong to said subset of nodes.

2. The apparatus according to claim 1, wherein said node configurator (102) is adapted to initially set said network node (10) into said relaying operation mode so as to build and advertise neighborhood information deduced from observed beacons of neighboring nodes.

3. The apparatus according to claim 1, wherein said node configurator (102) comprises a neighbor detection unit (1021) for collecting said neighborhood information from beacons received from neighboring nodes.

4. The apparatus according to claim 2, wherein said node configurator (102) is adapted to maintain said initial relaying operation mode until it has not observed any changes in said neighborhood information for a predetermined period of time.

5. The apparatus according to claim 1, wherein said node selector (1022) is configured to select said subset of nodes based on said neighborhood information and an additional seniority information collected from neighboring nodes, said seniority information indicating a node with the highest address in a neighbor list.

6. The apparatus according to claim 1, wherein said node configurator (102) is adapted to set up an access point interface and either a mesh interface or at least one station interface, if said network node (10) belongs to said selected subset, and to set up a station interface only, if said network node (10) does not belong to said selected subset.

7. A wireless node for a wireless mesh network, said wireless node comprising an apparatus according to any one of claims 1 to 6.

8. A station management entity for a wireless mesh network, said station management entity comprising an apparatus according to any one of claims 1 to 6, wherein said apparatus comprises a Media Access Control (MAC) layer interface for providing said neighborhood information.

9. A method of controlling a network node (10) of a wireless mesh network, said method comprising the steps of:

selecting a subset of nodes of said mesh network as relaying nodes based on a neighborhood information collected at said network node (10) from neighboring nodes; and

setting said network node (10) into a relaying operation mode, in which said network node (10) is controlled to beacon and participate in a formation of said mesh network, if said network node (10) belongs to said subset of nodes, setting said network node (10) into a non-relaying operation mode, in which said network node (10) is controlled not to beacon and not to participate in the formation of said mesh network, if said network node (10) does not belong to said subset of nodes.

10. A computer program product comprising code portions for performing the steps of a method according to claim 9 when said product is run on a computer device.