**High Throughput Path Establishment for Common Traffic in Wireless Mesh Networks**

Hassen A. Mogaibel, Mohamed Othman, Shamala Subramaniam and Nor Asilah Wati Abdul Hamid

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/48723

## **1. Introduction**

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Recently, Wireless Mesh Networks (WMNs) technology has gained a lot of attention and become popular in the wireless technology and the industry fields. This rising popularity is due to its low cost, rapid development and ability to offer broadband wireless access to the internet in places where wired infrastructure is not available or worthy to be deployed [2].

Wireless Mesh Networks (WMNs) consist of mesh routers that collect and forward the traffic generated by mesh clients. Mesh routers are typically fixed and equipped with multiple radio interfaces. Mesh clients are mobile, and data are forwarded by mesh routers to the intended destination. One or more mesh routers may have gateway functionality and provide connectivity to other networks such as internet access, as shown in Fig. 1. In the WMNs, most of the flows are between the mesh client and the gateway; this kind of traffic is called internet traffic which is the common WMNs traffic as users need to access wired resources.

Gateway discovery approaches in multihop wireless mesh network can be categorized into three categories as follows:


2 Will-be-set-by-IN-TECH 228 Wireless Mesh Networks – Effi cient Link Scheduling, Channel Assignment and Network Planning Strategies High Throughput Path Establishment for Common Traffic in Wireless Mesh Networks <sup>3</sup>

1. Static channel assignment: In a static channel assignment approach, each interface is assigned to a channel for long time durations. Static assignment can be further classified

High Throughput Path Establishment for Common Traffi c in Wireless Mesh Networks 229

(a) Common channel approach: In this approach, the radio interfaces of all nodes in the network are assigned to common channels [10]. For example, if two interfaces are used at each node, then the two interfaces are assigned to the same two channels at every

(b) Varying channel approach: In this approach, the radio interfaces in different nodes may be assigned to different channels [19, 26]. With this approach, it is possible that the length of the routes between nodes may increase, also, the network partitions may arise due to the inability of different neighbors to communicate with each other unless

2. Dynamic channel assignment: The dynamic channel assignment approach allows any interface to be assigned to any channel, and interfaces can frequently switch from one channel to another [31]. Therefore, a network using such a strategy needs some kind of synchronization mechanism to enable communication between nodes in the network. The benefit of dynamic assignment is the ability to switch an interface to any channel, thereby, offering the potential to use many channels with few interfaces. However, the key challenges are channel switching delays, and the necessity for coordination mechanisms

3. Hybrid channel assignment: In the hybrid approach, all the nodes are equipped with multi-radio interfaces in which the multiple radios are divided into two groups, fixed group and switchable group. In the fixed group, each radio interface is assigned a fixed channel for receiving packets, thereby, ensuring the network connectivity, while the

However, most of the previous research focuses on how to answer this question without

• Most of the traffic in WMNs is designated at the gateways as the users need to access the internet or wired resources. This kind of traffic can be considered as a multi-source single

• The local traffic and internet traffic must pass through the backbone nodes to reach their destination. Thus, improving the backbone performance will increase the WMN's

• Availability of multi-links between adjacent mesh routers makes the mesh routers support

The unique characteristics of WMNs motivated us to developed On-demand Channel Reservation Scheme (AODV-MRCR) with aims to establish high throughput path for the gateway traffic, reduces the interference caused by local traffic, supports full duplex node and only assigns channel to the active node. We achieve these objectives by integrated the

The reactive approach is choosing in order to establish high throughput paths for the gateway traffic and assigns channel to active node. This meaning that all nodes will statically assign common channels to their interfaces, and only the node that has gateway traffic allowed to switch some of its interfaces to the selected channels. Our contributions are as follows:

switchable group can dynamically switch among the other data channels [17].

considering the unique properties of WMNs, which include the following:

simultaneous multi-flow transmission for both kinds of the traffic.

reactive routing protocol with channel distribution.

into two types:

node.

they assign a common channel.

to switch between node channels.

destination traffic.

performance.

**Figure 1.** Multi-radio wireless mesh networks.

RREQ\_I, it unicasts back a Route Reply (RREP) message with an "I" flag (RREP\_I), which, among other things, contains the IP address of the gateway [5, 13, 36]. The advantage of this approach is that the control messages are only generated when a mesh node needs information about a reachable gateway. However, this approach may increase the packet end-to-end delay since the external path is not always available.

3. Hybrid approach: To consider the advantages of the proactive and reactive approaches, they can be combined into a hybrid proactive/reactive method for gateway discovery. For mesh router nodes in a certain range around a gateway, the proactive gateway discovery is used while the mesh router nodes residing outside this range use the reactive gateway discovery to obtain information about the gateway [18, 27, 39]. The approach provides good network connectivity while reducing the overhead. However, the main issue is the optimal value of the advertisement zone.

WMN capacity is reduced by interference from concurrent transmissions. There are two types of interference that affect the throughput of WMN, intra-flow and inter-flow interferences. The intra-flow interference refers to the interference between intermediate nodes sharing the same flow path, whereas, inter-flow interference refers to the interference between neighboring nodes competing on the same busy channel. These come from the half duplex of the radio and the broadcast nature of the wireless medium [21, 35].

Several approaches have been proposed to improve the WMN capacity. One approach is that each mesh router uses a single radio interface that dynamically switches to a wireless channel with a different frequency band to communicate with different nodes [4, 31]. However, this approach increases the routing overhead due to a switching delay. A more practical approach uses multiple radio interfaces that are dedicated to non-overlapping channels [1, 19, 32].

The IEEE 802.11 b/g and IEEE 802.11a standards define three and twelve non-overlapping channels (frequencies) [1, 8, 17]. One of the most important issues for the design of multi-radio multi-channel networks is how to bind the radio interface to a channel in a way that maintains network connectivity. Three approaches have been proposed t solve the channel assignment problem in multi-radio multi-channel WMNs which can be described as flowing:

1. Static channel assignment: In a static channel assignment approach, each interface is assigned to a channel for long time durations. Static assignment can be further classified into two types:

2 Will-be-set-by-IN-TECH

Internet

Mesh Router

RREQ\_I, it unicasts back a Route Reply (RREP) message with an "I" flag (RREP\_I), which, among other things, contains the IP address of the gateway [5, 13, 36]. The advantage of this approach is that the control messages are only generated when a mesh node needs information about a reachable gateway. However, this approach may increase the packet

3. Hybrid approach: To consider the advantages of the proactive and reactive approaches, they can be combined into a hybrid proactive/reactive method for gateway discovery. For mesh router nodes in a certain range around a gateway, the proactive gateway discovery is used while the mesh router nodes residing outside this range use the reactive gateway discovery to obtain information about the gateway [18, 27, 39]. The approach provides good network connectivity while reducing the overhead. However, the main issue is the

WMN capacity is reduced by interference from concurrent transmissions. There are two types of interference that affect the throughput of WMN, intra-flow and inter-flow interferences. The intra-flow interference refers to the interference between intermediate nodes sharing the same flow path, whereas, inter-flow interference refers to the interference between neighboring nodes competing on the same busy channel. These come from the half duplex of

Several approaches have been proposed to improve the WMN capacity. One approach is that each mesh router uses a single radio interface that dynamically switches to a wireless channel with a different frequency band to communicate with different nodes [4, 31]. However, this approach increases the routing overhead due to a switching delay. A more practical approach uses multiple radio interfaces that are dedicated to non-overlapping channels [1, 19, 32].

The IEEE 802.11 b/g and IEEE 802.11a standards define three and twelve non-overlapping channels (frequencies) [1, 8, 17]. One of the most important issues for the design of multi-radio multi-channel networks is how to bind the radio interface to a channel in a way that maintains network connectivity. Three approaches have been proposed t solve the channel assignment

problem in multi-radio multi-channel WMNs which can be described as flowing:

Mesh Client

optimal value of the advertisement zone.

**Figure 1.** Multi-radio wireless mesh networks.

Mesh Router

Mesh Router With Gateway

end-to-end delay since the external path is not always available.

the radio and the broadcast nature of the wireless medium [21, 35].

Wired Link Wireless Link

Mesh Client

Mesh Client

Mesh Router


However, most of the previous research focuses on how to answer this question without considering the unique properties of WMNs, which include the following:


The unique characteristics of WMNs motivated us to developed On-demand Channel Reservation Scheme (AODV-MRCR) with aims to establish high throughput path for the gateway traffic, reduces the interference caused by local traffic, supports full duplex node and only assigns channel to the active node. We achieve these objectives by integrated the reactive routing protocol with channel distribution.

The reactive approach is choosing in order to establish high throughput paths for the gateway traffic and assigns channel to active node. This meaning that all nodes will statically assign common channels to their interfaces, and only the node that has gateway traffic allowed to switch some of its interfaces to the selected channels. Our contributions are as follows:

(i) Enhance the capability of the node to receive and transmit concurrently by ensure that distinct channel should be reserved for the reverse and forward routing entry for each node involve in path establish process during the gateway discovery process.

the algorithm to update the gateway tables. Based on the new tables, it recalculates the link ranking and channel assignment. However, in general, the centralized approach causes a high computation overhead at the centric node and it is unwieldy in use due to the need for gathering network information. Moreover, most of them are static assignment which is not optimally utilizing the limited number of available non-overlapping channels. In contrast, our approach is a more dynamic approach, which is performed during the real-time networking;

High Throughput Path Establishment for Common Traffi c in Wireless Mesh Networks 231

Other studies assume that the traffic profile of each mesh router is not known, and usually consider channel assignment and routing separately. The authors of [25] assumed that the traffic from the Internet gateway to clients is dominant, and thus proposed distributed channel assignment based on spanning tree topology, where the gateway is the root of the spanning tree. The protocol dedicates one interface channel for communication with its parent node on the tree, and the other interfaces are configured as children for communication with their child nodes. Hence, the protocol divides the node interfaces into two subsets - downlink and uplink interfaces. The uplink interfaces are used to connect the node with its parent node while the downlink is used to connect the node with its child nodes. The node can only switch its child. For channel assignment, the channel assignment strategy starts from the root of the tree. Each node switches its parent interfaces to the parent node child interface and selects a new channel for its child interfaces. One drawback of this protocol is that it only considers the common traffic where data are transmitted from the source to gateway and vice versa.

Multi-channel routing protocol (MCR) [17] the peer-to-peer traffic was assumed to be dominant in the network. The authors first constructed a k-connected backbone from the original network topology, and then assigned channels on the constructed topology. The MCR classified the node interfaces into fixed or switchable interfaces. The protocol assigns a fixed channel to the fixed interface for communication between neighbors, and the remaining interfaces are considered as switchable interfaces. When a node wants to communicate with others, it looks in its table to find the destination's fixed channel and switches one of the switchable interfaces to that channel. To exchange fixed channels between neighbors, MCR uses a "hello" message to carry the fixed channel information. However, this protocol may not work well in a multi-flow transmission because of high switching interfaces and because it does not utilize all the non-overlapping channels as the static channel assignment uses.

Although there are many distributed solutions proposed in literature [7, 9, 16, 23, 25, 38]. In [16], the authors proposed the Local Channel Assignment (LCA) algorithm, which adopts a tree-based routing protocol for common traffic similar to Hyacinth. The LCA algorithm solved the Hyacinth interface-channel assignment conflict problem which is caused when a parent switches to the least load channel that may be in use by one of its children. The interface-channel assignment problem may cause recursive channel switching and delays. LCA solved this problem by dividing the non-overlapping channel into groups and making each parent interface belong to one group different from its child interface group. The paper of [7] proposed a distributed joint channel assignment and routing protocol for multi-radio multi-channel ad hoc network. The scheme dedicates one interface for the control message and another interface for data transmission. The control interface is assigned to a common channel while the data interfaces could work as a fixed or switchable interface based on the receiving call direction. However, in this approach, the control interface becomes the

In the paper of [9], the authors proposed a hybrid multi-channel multi-radio wireless mesh network architecture, which combines the advantages of both static and dynamic channel

in addition, no prior knowledge of the traffic profile is needed.

bottleneck, especially in high-density networks.


The remainder of the chapter is organized as follows. Section two discusses relevant work. The AODV-MRCR protocol is explained in section three. In section four, we provide the details of our simulation environment. Simulation results and their analysis are presented in section five, with concluding remarks in section six.
