an efficient wireless mesh network a new architecture 指導教授：許子衡 教授...

An Efficient Wireless Mesh Network A New Architecture

指導教授：許子衡 教授學生：王志嘉

Introduction (i)

WMN is composed of Wireless Mesh Routers (WMR), which offer connectivity to clients by acting as APs, forming at the same time a self-organized wireless backbone.

The gateway/bridge functionalities in mesh routers enable the integration of WMNs with various other networks.

Introduction (ii)

We use ad hoc networking protocol for WMN in order to route discovery, table maintenance.

One can use ad hoc networking protocol for WMN those are defined for ad hoc network only where all participating node are totally mobile.

That is if you use current ad hoc network protocol for WMN it will not be able to take advantages of some fixed node

Existing Architecture of WMN – Overview (i)

Wireless mesh network is a mesh of networks.

It is a network which gives the flexibility to communicate between different types of networks like Sensor Network, Wi-Fi Network, and Wi-Max Network etc. It consists of two types of nodes: Mesh routers and Mesh Clients.

Existing Architecture of WMN – Mesh router

It is similar to the conventional router and has the same routing functions of the conventional router.

It also includes gateway or bridge or repeater functions to communicate with different types of network like Sensor Network,Wi-Fi Network, and Wi-Max Network.

Mesh routers are minimal mobile. They construct the backbone of the network for the mesh clients. They are self-configured, self-healed.

Existing Architecture of WMN – Mesh client

It is similar to the conventional client but it is mobile.It additionally includes routing capabilities to support mesh network.

It doesn't include gateway or bridge or repeater functions for the support of communication with different network.

Existing Architecture of WMN--Architecture

Three types of architectures exist for WMN. They are ： Infrastructure / Backbone WMN,client WMN,and hybrid WMN.

Infrastructure / Backbone WMN (i)

These mesh routers form a backbone or infrastructure for the mesh clients, as shown in Fig 1.

This backbone supports the access to different types of network like Sensor Network, Wi-Fi Network,Wi-Max Network and the Internet

Fig.1

Infrastructure / Backbone WMN (ii)

Mesh routers can be connected directly to the Internet. But to communicate with other networks it must be connected through the access point or base station of them.

Clients of other networks should connect to the mesh router through their base station or access point.

Client WMN

This network is built only with mesh clients. No mesh routers are involved here as shown in Fig 2.

They will communicate with same radio technology. Their communication is peer-to-peer.

Hybrid WMN

This network is built by meshing the mesh routers and the mesh clients as shown in Fig 3.

Here mesh routers form the backbone for clients exactly as in Infrastructure WMN.

The mesh clients have the advantage to be connected to the internet through the mesh router. They can also communicate the clients of other types of networks such as Sensor, Wi-Fl, and Wi-Max etc through mesh routers.

Fig.3

Proposed Architecture of WMN--Overview

Our proposed architecture is almost same as hybrid WMN. But here we consider an extra special purpose mesh router that called master mesh router. The proposed architecture is shown in Fig. 4.

Fig.4

Proposed Architecture of WMN--Mesh Router

Mesh router maintains three types of table such as client table, routing table and cache table. Client table contains the information of mesh client.

The routing table contains the best path of this router to other mesh routers including master mesh router.

The cache table contains the recent visited paths to mesh client via this router.

Connectivity Ensure Using Hello Message

Mesh routers send Hello message within specified time period to ensure connectivity. But all mesh routers don't send Hello message. Particular mesh routers only send and check the connectivity

To determine the router head, mesh routers execute an algorithm 'Router Head Selection Algorithm'.

Connectivity Ensure Using Hello Message

The basic function of that algorithm is as follows ：1. It fast selects a mesh router as a router head whose ma

ximum number of adjacent mesh router and constructs a cell with its adjacent routers as shown in Fig.5

2. Select a gateway router among the adjacent of router head whose maximum number of adjacent and minimum number of adjacent is member of existing cell.

Fig.5

Connectivity Ensure Using Hello Message

3. Now the gateway router selects a adjacent router as router head whose maximum number of adjacent and minimum number of adjacent is member of existing cell.

4. If an adjacent of gateway has no adjacent and is not member of any cell then gateway takes special care of that router.

Connectivity Ensure Using Hello Message

After selecting router head and gateway router, only router heads send Hello message to its neighbor.

If a mesh router is shutdown then router head detects it or if a router head is shutdown then gateway router detects it. So connectivity is ensured here.

Tables Maintenance

The routing table holds the information of other mesh router includes master mesh router.

The format of routing table is shown in Fig.6. Two type of path to access a mesh router are store

in the routing table. Strong Path is only use the strong link. On the other hand the weak path uses either strong link or weak link or combination of both.

Fig.7. is shown the strong path and weak path.

Fig.6

Fig.7

Reduce network traffic

To ensure connectivity router head and gateway router only send Hello message within specified time period. But other mesh routers don't send Hello message. Using this technique the amount of network traffic can be reduced.

When mesh router want to use that link but it's not valid it just update its routing table and uses strong path.

Drawbacks

The disadvantage of having a router head scheme is that frequent router head changes can adversely affect routing performance since mesh router are busy in router head selection rather than packet relaying.

Mesh Client

The mesh clients are the end user in the network. A mesh client stores information about its

neighbor in this table. Mesh clients stay on the common zone of one

more mesh router. In this circumstance, it stores only one mesh router's information that is how to access that mesh router.

Route Maintenance

A client wants t o join this network. It fast broadcasts the Update message.

Mesh router receives Update message and send unicast Update message to master router that a mesh client join.

The other mesh clients receive Update message and update their neighbor table. If a mesh client is down or changes its position then mesh router and mesh client will detect that by using Hello message and they will change their corresponding table.

Route Maintenance

Now a client of a mesh router wants to access another client. The wanted client may stay its neighbor or the same mesh router but not neighbor or different mesh router.

Otherwise it sends Route Request to mesh router. If not available then mesh router send Route Request to master mesh router. Master mesh router also check its client table if the require client is available then it sent to mesh router Route Reply.

Conclusion

According to our proposal this new architecture of WMN is efficient one. It has reduced overhead caused by route maintenance, route discovery.

Network traffic reduces dramatically than current status.

We can get relive from using ad hoc network routing protocol that is used now a day for WMN