**3. Quality of service in WiMAX networks**

WiMAX has been developed with QoS in mind. Five different service classes have been introduced for different applications and packets from different service classes and are being handled on the basis of their QoS constraints. However, this mechanism can only be used in the PMP (Point-to-Multipoint) mode. In the Mesh mode, QoS is maintained on a message-bymessage basis.

geographical mobility. The system will always know which jumps are required for the request of a customer at any point in the network so that it can reach the Internet in the most efficient

The growing interest in multimedia applications in mesh networks is accompanied by challenges that make the provision of QoS and group communication (multicasting) a more complex task. This complexity is the result, among other factors such as high mobility of the stations, which implies that there is a need to manage their locations and the environment and cope with the limitations of the devices involved, such as transmission quality in a wireless

Mesh networks have good prospects of being the solution to a series of problems in the provision of access services, since they are flexible, dynamic and potentially low cost [9]. However, for this to become effective there is much that needs to be improved and developed. Besides routing, the major problems in mesh networks are scalability and security. The first can be defined as the level of acceptable service packages in the presence of a large number of nodes in the network. An important factor is the potential reduction in performance when there are an increased number of nodes. Hence, any protocol layers involved should be scalable. The security schemes proposed for ad hoc networks can be adopted for mesh networks, although most of these solutions have not been studied in depth and there are still

problems that prevent them from providing authentication and reliability to clients.

quality of service using resource reservation and QoS for the data link layer.

key area of research of comparable importance to algorithms.

**3. Quality of service in WiMAX networks**

Today the provision of QoS to any network is mandatory. When the mesh networks follow these steps, with the growth of multimedia applications, the services often seek a guaranteed bandwidth and QoS requirements, as a result of the growth of multimedia applications [2] [10]. In addition, they know that choosing the best path routing is an important decision for the WMNs to enable them to provide a wide range of services to different client types, each with their own peculiar characteristics. Provisioning QoS in mesh networks is not devoted to a single task layer. It requires the joint effort of all the layers, and specific strategies for signaling

Owing to this and a number of other problems, when compared with other wireless network models, the mesh networks pose a special challenge, because the wireless environment is shared by adjacent nodes and the topology may change dynamically in the same way as the mobility of the nodes and input / output in the same network. As a result, QoS has become a

WiMAX has been developed with QoS in mind. Five different service classes have been introduced for different applications and packets from different service classes and are being handled on the basis of their QoS constraints. However, this mechanism can only be used in

manner possible.

66 Selected Topics in WiMAX

**2.2. Challenges and problems**

environment, bandwidth scarcity, etc.

In PMP mode, the WiMAX MAC layer uses a scheduling service to deliver and handle SDUs (Service Data Units) and MAC PDUs (Protocol Data Units) with different QoS requirements. A scheduling service uniquely determines the mechanism the network uses to allocate UL (UpLink) and DL (DownLink) transmission opportunities for the PDUs. WiMAX defines five scheduling services:


Classifiers are also present in the MAC layer of both the Base Station and Subscriber Station, whose goal is classify and map service flow into a particular connection for transmission between the MAC peers. The mapping process associates a data packet with a connection, which also creates a link with the service flow characteristics of this connection [11].

In this architecture there are schedulers in both the Base Station (BS) and Subscriber Station (SS), whose goal is to determine the burst profile and the transmission periods for each connection, while taking into account the QoS parameters associated with the service flow, the bandwidth requirements of the subscriber stations and the parameters for coding and modulation. Figure 4 illustrates the WiMAX QoS Architecture in PMP mode.

into a number of transmission opportunities. The data subframe is similarly divided into a

A Mobile WiMAX Mesh Network with Routing Techniques and Quality of Service Mechanisms

http://dx.doi.org/10.5772/55863

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There are two types of control subframes depending on their function. The first type of control subframe is the scheduling subframe in which nodes transmit scheduling messages. The second is the network configuration subframe in which nodes broadcast network configura‐ tion packets containing topology information, network provisioning information, and network

The IEEE 802.16 mesh standard uses a combination of a 16-bit mesh node identifier (node ID) and a 16-bit connection identifier (CID) to identify the source and destination of every transmission. The CID in mesh mode is a combination of an 8-bit link ID and an 8-bit QoS description for the connection. All the communications occur in the context of a link, which is established between two nodes. One link will be used for all the data transmissions between two nodes. QoS is provisioned over links on a message-by-message basis. No services or QoS parameter are associated with a link, but each unicast message has service parameters in the header. Figure 6 shows the Mesh connection identifier (CID) construction which contains these

The 8-bit QoS in the CID contains three definable fields: Reliability, Priority/Class, and Drop Precedence. Reliability refers to retransmit or not (0 indicates no retransmit while 1 indicates

number of minislots.

management messages.

**Figure 5.** Mesh frame structure

service parameter fields.

**Figure 6.** QoS bits in the mesh CID

**Figure 4.** Architecture for IEEE 802.16 QoS
