Analysis of Wireless Mesh Network Routing

Xiaolong Tan1, Jia Zhou

1, Wenbin Wang a,1

1Yalong River Hydropower Development Company LTD, Chengdu, 610051, China

aemail: wangwenbin@ylhdc.com.cn

Keywords: Mesh Network, Routing Overhead, Network Topology

Abstract: Since the wireless mesh network topology dynamics and the radio channels instable, the

design of wireless mesh network routing protocol become one of the key factors to determine the

performance. This paper mainly studied the existing several kinds of typical three-layer mesh

network routing protocol (DSDV and AODV), aimed at the defects of three-layer routing limited to

the network topology changes, the paper proposed a network model based on two-layer routing.

Forwarding the packet, establishing and maintaining the communication links are accomplished on

the Mac layer. Simulation tests showed that two-layer routing has a big improvement on the

efficiency of packet forwarding, and it effectively reduced the routing overhead and end-to-end

delay simultaneously.

Introduction

Wireless mesh network (WMN) is a dynamic self-organizing, self-configuring network. WMN

is mainly composed of mesh routers and mesh clients. All the nodes in a mesh network

automatically establish a dynamic network and maintain network connectivity [1] . Wireless mesh

network become one of the hot spots in current research due to its wide range of applications and

network flexibility, low cost, easy to expand and so on. WMN routing algorithm must be based on

the characteristics of multi-hop wireless networks to satisfy requirements.

Routing protocol analysis

DSDV protocol is a distance vector protocol. The design idea is to maintain a monotonically

increasing sequence number of the destination node for each route. In the case of don't need to

collaborate with adjacent nodes, contrast the serial number of nodes to prevent appearing routing

loops [2] . DSDV protocol stipulates that the destination node serial number stored in the routing

table entry of each network node. By joining in packet destination node domain, the destination

node distance information exchanged mutually in the adjacent nodes with each routing updates. In

this way, each node using the distance vector received from the neighbor node to update their

routing table, to make sure the current routing is latest and best.

But in the condition of network topology changes frequently and high-speed mobile nodes, the

convergence performance of DSDV protocol will worsen sharply. Whether the node needs to send

data or not, it requires broadcasting updating information to the adjacent nodes periodically. So, the

more nodes join in the network, the larger the network traffic density, and the capacity, cost of the

routing table and bandwidth increasing will increase network load [3] . Limited network scale is the

main drawback of DSDV protocol.

AODV is a typical on-demand routing protocol. It is proposed based on the DS-DV algorithm

and combined the on-demand routing mechanism of DSR algorithm.

Design of routing scheme

In fact, the performance of the variety three-layer routing protocols are different in the specific

different networks, the complexity of the network topology has a lot to the conditionality of

marketable by the performance of the agreement, The complexity of the network topology has a lot

conditionality to the performance of the protocol.

Advanced Materials Research Vols. 989-994 (2014) pp 4629-4632 Submitted: 25.05.2014Online available since 2014/Jul/16 at www.scientific.net Accepted: 29.05.2014© (2014) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.989-994.4629

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 141.117.125.1, Ryerson University Lib, Toronto-03/12/14,07:12:35)

Two-layer routing protocol is the proactive routing protocols based on node topology. It can be

implemented by either centralized or distributed strategies. The differences between two-layer

routing protocols and traditional protocols are: the two-layer protocols address by the MAC address

and forward through two layers [4] . The upper layer protocol stack do not need for additional

splitting and encapsulation. Neighbors, topology built and maintained in MAC layer, requires no

additional sending notice, updating routing messages to create and maintain the routing. This can

reduce the system overhead brought by the routing protocol, save bandwidth, and reduce the

delay [5] . Especially suitable for the multi-hop networks with high real-time demand of data

transmission, large number of nodes and complicated network structure.

Here discussed the mesh node routing, assume a neighbor relationship table:

1 2 3 4 5

1 0 1 0 0 0

2 1 0 1 1 1

3 0 1 0 1 1

4 0 1 1 0 1

5 0 0 1 1 0

Node 1 as an example to describe the process of routing path discovery:

(1) The neighbor of node 1 (level 1) is node 2, record the arrival path:

1－＞2

(2) The neighbor of node 2 (level 2) is node 3, 4, record the arrival path:

1－＞2－＞3

1－＞2－＞4

(3) The neighbor of node 3 (level 3) is node 2, 4, 5, the arrived is no longer record:

1－＞2－＞3－＞5

Now found that all nodes have finished traversal, so the final routing information of node 1 is

as follows:

1－＞2

1－＞2－＞3

1－＞2－＞4

1－＞2－＞3－＞5

Routing addressing and data forwarding

Packet routing mainly involves the following several modules: Mac Layer, Mesh Route and

IPFM. The protocol stack is shown in figure 1:

(1)MAC Layer mainly responsible for the allocation of resources, time slot and conflict

avoiding and maintain network topology table topo_table and the neighbor table neighbour_table;

(2) Mesh Route is mainly responsible for network topology table obtained from the MAC

Layer, and calculates the two-layer routing and selects the path.

(3) IPFM forwarding management for IP, The main function is the forwarding of host routing

and the maintenance of host routing table host_table.

4630 Materials Science, Computer and Information Technology

Fig.1 Protocol stack model

In order to reduce the processing delay, we can use the mixed two-layer and three-layer mode

to forward. Increase the target node identification in forwarding data. If the destination node is not

itself after the receiver receives the data, then check the next-hop node of the target node by Mesh

Route, forwarding on the second layer and don’t need to check routing; If the destination node is

itself, then send to IPFM routing module to discover route and forward.

Test result

In this paper, we use NS2 software to simulate under the Linux operating system.

1000m×1000m simulation area uniformly distributed 50 wireless Mesh nodes. The distance

between each test nodes is larger than 100 m, and the maximum rate of mobile node is 25 m/s.

Under the same simulation scenario, by changing the movement speed of test node, we compare the

routing overhead and the average delay of typical three-layer AODV and two-layer routing

algorithm, and simulated the network throughput under different network topology.

Routing overhead refers to the amount of the average control group used to transmit a group

successfully. The selection of routing algorithm greatly influences the routing overhead.

Fig. 2 Routing overhead Fig.3 Average end-to-end delay

As shown in figure 2, two-layer routing has obvious more advantages in routing overhead than

AODV routing. The increase of node speed leads to greater risk of link disconnected, at this

moment need more system overhead to repair links. Since the stability of the node topology built

and maintained on MAC layer in the two-layer routing scheme, requires no additional sending

notice, updating routing messages to create and maintain the routing, improving the efficiency of

the routing and packet delivery success rate, also lower the number of the fixed link simultaneously,

thus largely reduces the network routing overhead.

The end-to-end delay is the time difference value of data packets from the source node to

destination node. It can effectively measure the time efficiency of the routing algorithm. The delay

jitter is particularly important for voice video stream demanding high real-time requirements.

As shown from the figure 3, with the change of node location and increase of speed, the

possibility of the routing path breakage increases and needs more extra time for topology stability

and routing reconstruction. So the end-to-end delay also increases accordingly. While the two-layer

routing forward the packet on the Mac layer. On the one hand, it reduced the encapsulation and

Advanced Materials Research Vols. 989-994 4631

splitting of protocol, and forward faster. On the other hand, maintain the link stability on Mac layer

is more quickly and efficiently than on the IP layer, so obviously reduces the end-to-end delay.

Conclusions

This paper studied and analyzed the characteristics and defects of the existing typical Ad Hoc

network/Mesh structure routing protocols, proposed the scheme design based on the two-layer

routing to forward the packet and establish and maintain communication links on the Mac layer.

Simulation tests show that packet forwarding on the second layer improving the efficiency of the

system delay and forwarding efficiency, especially suitable for complicated multi-hop networks.

References

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[4]. R. Draves, J. Padhye and B. Zill, "Routing in Multi-Radio, Multi-Hop Wireless Mesh

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4632 Materials Science, Computer and Information Technology

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