Design and Analysis of a Novel Hybrid Wireless Mesh Network Routing Protocol

1. Introduction

Wireless Mesh Networks (WMNs) or Mobile Ad hoc Networks (MANETs) are widely used networks in disaster management, security surveillance and emergency situations, since they have capability to manage and configure themselves without any external support. Generally WMNs are deployed using IEEE 802.11 standard devices and hardware infrastructures. In WMNs mesh nodes are connected wirelessly in multi-hop connectivity. Some of these are Mesh Routers that provide backbone infrastructure while Mesh Clients communicate in mobile ad-hoc mode having diverse node positions. Recently WMNs became very cost effective as there is no need of wired medium and can easily be deployed in longer distance without too much ground support. Most WMNs are applicable in emergency situations, intelligent transportation, military and community networks. For more mobility with optimal communication having minimal resource utilization and better QoS, many routing protocols are developed and deployed. Some of these are reactive (demand driven) and some are proactive (table driven).

MANETs have issues in routing and optimal solutions for minimizing delays and packet loss, which is a challenging task because of high mobility. Ad-hoc nodes can cause more link breakages and delay the transmission. In earlier schemes these issues were partially addressed, some of these were eliminated but few of them still are creating problems. In this research work we have strongly focused on hybrid WMN in which both infrastructure and mobile ad-hoc modes are involved. There are few protocols that are capable to operate in both modes simultaneously while most of these still have performance issues related to routing overheads.

The most widely used protocols in WMNs are AODV, which is reactive in nature, and DSDV, which is proactive. WMNs are divided into three basic types: infrastructure, client mesh and hybrid mesh. In this paper we will discuss the hybrid mesh networks. Hybrid Wireless Mesh Network (HWMN) is the combination of two modes of communications (Akyildiz, 2005): infrastructure (backbone) and ad-hoc (Client). In infrastructure mode Mesh Routers are involved in routing, however mesh clients are not directly involved in forwarding and routing packets as they get access to other nodes through mesh routers. In ad-hoc (Client Mesh) mode client nodes are independent. Hybrid mesh is the combination of both infrastructure and ad-hoc modes.

Normally, in reactive AODV routing protocol, a RREQ (Route Request) packet is generated from the source node for route discovery to destination. Source node broadcasts RREQ to all the neighbor nodes until the destination is found or an intermediate node knows the route to destination. Then a RREP (Route Reply) packet is generated and unicast back to the source, otherwise RREQ is rebroadcast and forwarded to next nodes. A TTL (Time To Live) parameter is incremented each time a RREQ is broadcast. If this timer gets expired and destination not found or link breakage occurs, RERR (Route Error) message is sent back to source node and AODV performs a local route repair. This process is explained in Figure 1.

Figure 1.

AODV route discovery