Introduction Of Wireless Mesh Networks

Published Date: 02 Nov 2017

Wireless mesh networks (WMNs) are dynamically self-organize and self-configured. WMNs are constructed of two types of nodes: first is mesh router and second is mesh client. Other than the routing capability for gateway/bridge functions as in a normal wireless router, a mesh router contains extra routing functions to support networking in mesh. Although multi-hop communications, the same coverage can be achieved by a mesh router with much lower transmission power.

A router in wireless mesh networks is usually equipped with multiple wireless interfaces built on either the same or different wireless access technologies. Besides of all these differences, mesh and wireless routers are usually built based on a same hardware platform.

Mesh routers have minimum 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 WMNs, 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.

Characteristics of a WMN

■ WMN‘s are considered to be a subclass of ad hoc networking

--> Routing nodes are stationary (unlike in Mobile Ad Hoc Networks, MANET‘s)

■ WMN‘s have properties of an autonomic system:

- Self-Configuration

- Self-Healing (redundant, decentralized, no central point of failure)

- Self-Managment

- Self-Optimization

--> Challenging tasks for a good system design

â–  High overall capacity:

- Spatial diversity

- Power management

Important constraints:

- Shared bandwidth & interference

- Number and location of nodes

The type of WMNs can be classified into three types:

Backbone WMNs: In backbone WMN, mesh routers form an infrastructure for clients, where dashed and solid lines indicate wireless and wired links, respectively. The WMN backbone can be built using various types of radio technologies. The mesh routers make a mesh of self-configuring, self-healing links among themselves .With the help of gateway , mesh routers can be connected to the Internet. This is 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. Clients with an Ethernet interface can be connected to mesh routers via Ethernet links. For clients with the same radio technologies as mesh routers, they can directly communicate with mesh routers. If other radio technologies are used, clients must communicate with their base stations that have Ethernet connections to mesh routers.

Client WMNs. Client WMNs provides peer-to-peer networks among client nodes. In client WMNs, 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.

Design Factors

The design factors for the performance of WMNs are given as follows.

Radio Techniques in WMN: Many research work have been done to increase capacity of wireless systems in past years. Examples include directional and smart antennas, multiple input multiple output (MIMO) systems, and multi-radio/multi-channel systems. To further improve the performance of a wireless radio and control by higher layer protocols, more advanced radio technologies, such as reconfigurable radios, frequency agile/cognitive radios, and even software radios, have been used for wireless communication. Although these radio technologies are still in their infancy, they are expected to be the future platform for wireless networks due to their dynamic control capability. These advanced wireless radio technologies all require a revolutionary design in higher-layer protocols, especially MAC and routing protocols.

Scalability. Without support of this feature, the network performance degrades significantly as the network size increases. For example, routing protocols may not be able to find a reliable routing path, transport protocols may lose connections, and MAC protocols may experience significant throughput reduction. To ensure the scalability in WMNs, all protocols from the MAC layer to the application layer need to be scalable.

Mesh Connectivity. To ensure reliable mesh connectivity, network self-organization and topology control algorithms are needed. Topology-aware MAC and routing protocols can significantly improve the performance of WMNs[5].

Broadband and (QUALITY OF SERVICE) QoS. Different from classical ad hoc networks, most applications of WMNs are broadband services with heterogeneous QoS requirements. Thus, in addition to end-to-end transmission delay and fairness, more performance metrics, such as delay jitter, aggregate and per-node through- put, and packet loss ratios, must be considered by communication Protocols [3].

Security. Although many security schemes have been proposed for wireless LANs in recent years, they are still not fully applicable for WMNs. For instance, there is no centralized trusted authority to distribute a public key in a WMN due to the distributed system architecture. The existing security schemes proposed for ad hoc networks can be adopted for WMNs. However, most of the security solutions for ad hoc networks are still not mature enough to be implemented practically. Moreover, the different network architectures between WMNs and ad hoc networks usually render a solution for ad hoc networks ineffective in WMNs.

Ease of Use. Protocols must be designed to enable the network to be as autonomous as possible. In addition, network management tools need to be developed to efficiently maintain the operation, monitor the performance, and configure the parameters of WMNs. These tools, together with the autonomous mechanisms in networking protocols, enable rapid deployment of WMNs.

Compatibility and Inter-operability. In WMNs it is a default requirement to support network access for both conventional and mesh clients. Therefore, WMNs need to be backward compatible with conventional client nodes. This demands that mesh routers need to be capable of integrating heterogeneous wireless networks.[2]

Advances and Research Challenges

The distinct features and critical design factors of WMNs bring many challenging issues to communication protocols, ranging from the physical layer to the application layer. Despite recent advances in the research and development in WMNs, many challenging problems still remain:[1] the theoretical network capacity is still unknown, protocols in various layers need to be improved, new schemes are required for network management, and the network still lacks security.

WIRELESS MESH Network Management

Many management functions are needed to maintain the appropriate operation of WMNs. Mobility Management. A distributed mobility management scheme is needed for WMNs. However, because of the existence of a backbone network, a distributed scheme for WMNs can be simpler than that for mobile ad hoc networks. How to take advantage of the network backbone to design a lightweight distributed mobility management scheme for WMNs needs further investigation. Mobility management is closely related to multiple layers of network protocols, so developing multi-layer mobility management schemes is another interesting research topic. Location service is a desired feature by WMNs. Location information can enhance the performance of MAC and routing protocols, and it can help to develop promising location related applications. Proposing accurate or efficient algorithms for location service is still an open research topic.

Power Management

The goal of power management in WMNs varies with network nodes. Usually, mesh routers do not have a constraint on power consumption; power management aims to control connectivity, interference, spectrum spatial- reuse, and topology. In contrast to mesh routers, mesh clients may expect protocols to be power-efficient. Thus, it is quite possible that WMNs require power management to optimize both power efficiency and connectivity, which results in a complicated problem.

Network Monitoring. Many functions are performed in a network management protocol. The statistics in the management information base (MIB) of mesh nodes especially mesh routers; need to be reported to one or several servers in order to continuously monitor network performance. In addition, data processing algorithms in the performance monitoring software on the server analyze these statistical data and determine potential abnormalities. Based on the statistical information collected from the MIB, data processing algorithms can also accomplish many other functions such as network topology monitoring.