Network Architecture And Critical Design Factors

Published Date: 02 Nov 2017

Introduction

Wireless mesh networks (WMNs) are dynamically self-organized

and self-configured, with the nodes in the network automatically

establishing an ad hoc network and maintaining the

mesh connectivity. WMNs are comprised of two types of

nodes: mesh routers and mesh clients. Other than the routing

capability for gateway/bridge functions as in a conventional

wireless router, a mesh router contains additional routing

functions to support mesh networking. Through multi-hop

communications, the same coverage can be achieved by a

mesh router with much lower transmission power. To further

improve the flexibility of mesh networking, a mesh router is

usually equipped with multiple wireless interfaces built on

either the same or different wireless access technologies. In

spite of all these differences, mesh and conventional wireless

routers are usually built based on a similar hardware platform.

Mesh routers have minimal mobility and form the mesh

backbone for mesh clients. Thus, although mesh clients can

also work as a router for mesh networking, the hardware platform

and software for them can be much simpler than those

for mesh routers. For example, communication protocols for

mesh clients can be light-weight, gateway or bridge functions

do not exist in mesh clients, only a single wireless interface is

needed in a mesh client, and so on.

In addition to mesh networking among mesh routers and

mesh clients, the gateway/bridge functionalities in mesh

routers enable the integration of WMNs with various other

networks. Conventional nodes equipped with wireless network

interface cards (NICs) can connect directly to WMNs through

wireless mesh routers. Customers without wireless NICs can

access WMNs by connecting to wireless mesh routers through,

for example, Ethernet. Thus, WMNs will greatly help users to

be always-on-line anywhere, anytime.

Consequently, instead of being another type of ad-hoc networking,

WMNs diversify the capabilities of ad-hoc networks.

This feature brings many advantages to WMNs, such as low

up-front cost, easy network maintenance, robustness, reliable

service coverage, etc. Therefore, in addition to being widely

accepted in the traditional application sectors of ad hoc networks,

WMNs are undergoing rapid commercialization in

many other application scenarios such as broadband home networking,

community networking, building automation, highspeed

metropolitan area networks, and enterprise networking.

To date, several companies have already realized the

potential of this technology and offer wireless mesh networking

products. A few testbeds have been established in university

research labs. However, for a WMN to be all it can be,

considerable research efforts are still needed. For example,

the available MAC and routing protocols are not scalable;

throughput drops significantly as the number of nodes or hops

in WMNs increases. Thus, existing protocols need to be

enhanced or re-invented for WMNs. Researchers have started

to revisit the protocol design of existing wireless networks,

especially of IEEE 802.11 networks, ad hoc networks, and

wireless sensor networks, from the perspective of wireless

mesh networking. Industrial standards groups, such as IEEE

802.11, IEEE 802.15, and IEEE 802.16, are all actively working

on new specifications for WMNs.

In this article we present a survey of recent advances in

protocols and algorithms for WMNs. Our aim is to provide a

better understanding of research challenges of this emerging

technology. The rest of this article is organized as follows. The

network architectures of WMNs are first presented, with an

objective to highlight the characteristics of WMNs and the

critical factors influencing protocol design. A detailed study

on recent advances of WMNs is then carried out, with an

emphasis on open research issues. The article concludes with

final remarks.

Network Architecture and Critical Design Factors

Network Architecture

The architecture of WMNs can be classified into three types:

Infrastructure/Backbone WMNs. In this architecture, mesh

routers form an infrastructure for clients, as shown in Fig. 1,

where dashed and solid lines indicate wireless and wired links,

respectively. The WMN infrastructure/backbone can be built

using various types of radio technologies, in addition to the

mostly used IEEE 802.11 technologies. The mesh routers

form a mesh of self-configuring, self-healing links among

themselves. With gateway functionality, mesh routers can be

connected to the Internet. This approach, also referred to as

infrastructure meshing, provides a backbone for conventional

clients and enables integration of WMNs with existing wireless

networks, through gateway/bridge functionalities in mesh

routers. Conventional clients with an Ethernet interface can

be connected to mesh routers via Ethernet links. For conventional

clients with the same radio technologies as mesh

routers, they can directly communicate with mesh routers. If

different radio technologies are used, clients must communicate

with their base stations that have Ethernet connections to

mesh routers.

Client WMNs. Client meshing provides peer-to-peer networks

among client devices. In this type of architecture, client

nodes constitute the actual network to perform routing and

configuration functionalities as well as providing end-user

applications to customers. Hence, a mesh router is not

required for these types of networks. Client WMNs are usually

Abstract

Wireless mesh networks (WMNs) have emerged as a key

technology for next-generation wireless networking. Because

of their advantages over other wireless networks, WMNs are

undergoing rapid progress and inspiring numerous applications.

However, many technical issues still exist in this field. In

order to provide a better understanding of the research challenges

of WMNs, this article presents a detailed investigation

of current state-of-the-art protocols and algorithms for

WMNs. Open research issues in all protocol layers are also