**2.1. Operation**

another in different ways. Mesh type networks have the advantage of being low cost, easy to

In another analogy, a wireless mesh network can be regarded as a set of antennas, which are spaced a certain distance from each other so that each covers a portion or area of a goal or region. A first antenna covers an area, the second antenna covers a continuous area after the first and so on, as if it were a tissue cell, or a spider web that interconnects various points and wireless clients. What is inside these cells and covers the span of the antennas, can take advantage of the network services, provided that the client has a wireless card with the

Mesh networks are networks with a dynamic topology that show a variable and constant change with growth or decline, and consist of nodes whose communication at the physical level occurs through variants of the IEEE 802.11 and IEEE 802.16 standard, and whose routing is dynamic. The image below (Figure 2) shows an example of a mesh network. In mesh

To achieve these goals, WiMAX networks can be structured into two operating modes: PMP (Point-to-Multipoint) and mesh networks, and the second is the focus of this chapter. Mesh mode is a type of operation that can interconnect multiple mobile clients together with many WiMAX base stations (nodes) and form a network of connections so as to provide a wide coverage area for mobile clients. All the clients can communicate with each other and there is no need for an intermediate node to act as the mediator of the network. In this mode, the IEEE

networks, the access point / base stations area is usually fixed.

deploy and reasonably fault tolerant.

interface technology.

64 Selected Topics in WiMAX

**Figure 2.** Mesh network

The most effective way to discover the operation of the mesh network is the routing protocol, which scans the different possible routes / paths of data flow, on the basis of a pivot table where devices such as BS select the most efficient route to follow to reach a goal, while taking into account that the greater the speed, the packet loss, or the faster the access to the Internet (and others). This scan is carried out several times per second and is transparent to the user, even when it occurs at re-routing access gateways, which are the nodes that have direct access to the internet.

An important feature of mesh networks is the concept of roaming, also known as a transparent handoff mobility scheme offering fast handoff in wireless networks. This makes it feasible for users to become mobile clients who can move around between network nodes without losing the connection at the time of exchange. The practical consequence is that the system allows 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 manner possible.

the PMP (Point-to-Multipoint) mode. In the Mesh mode, QoS is maintained on a message-by-

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

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

67

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

**1.** Unsolicited grant service (UGS): This is designed for the real-time constant bit rate (CBR) applications such as T1/E1 and VoIP. Unsolicited data grants are allocated to eliminate the overhead and latency of the request/grant process. During the connection establish‐ ment phase, maximum sustained traffic rate is declared and BS assigns fixed bandwidth

**2.** Real-time polling service (rtPS): This is designed to support real-time services that generate variable-size data packets on a periodic basis, such as MPEG (Motion Pictures Experts Group) video. In this scheduling service, the BS provides unicast polling oppor‐ tunities for the MS to request bandwidth. The unicast polling opportunities are frequent

**3.** Extended real-time polling service (ertPS): This scheduling service combines features from UGS and rtPS service classes. An initial ensured bandwidth allocation is carried out as in UGS and then this allocated bandwidth can be decreased or increased as in the case of

**4.** Non-real-time polling service (nrtPS): This scheduling service is the most appropriate for the delay tolerant applications. As in rtPS, dedicated periodic slots are used for the bandwidth request opportunity, but with much longer periods. In nrtPS, it is allowable to have unicast polling opportunities, but the average duration between two such opportunities is in the order of a few seconds, which is large compared to rtPS. All the MSs belonging to the group can also request resources during the contention-based

polling opportunity, which can often result in collisions and additional attempts.

opportunities as long as there is space available [1] [2].

**5.** Best effort (BE): This provides very little QoS support and is applicable only for services that do not have strict QoS requirements. It is for the traffic with no minimum level of service requirements. Like in nrtPS, contention slots are used for bandwidth request

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,

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

which also creates a link with the service flow characteristics of this connection [11].

enough to ensure that latency requirements of real-time services are met.

message basis.

scheduling services:

rtPS.

grants in each frame accordingly.
