Wimax standards and Security The Wimax

FIGURE 3.3
Overview of dynamic service flow.
IEEE 802.16 also supports dynamic service changes in which service flow parameters are renegotiated. Like dynamic service flow establishment, ser- vice flow changes also follow a similar three-way handshaking protocol. Service flows may be created, changed, or deleted. This is accomplished through a series of MAC management messages referred to as DSA, DSC, and dynamic service delete (DSD). The DSA messages create a new service flow, the DSC messages change an existing service flow, and the DSD messages delete an existing service flow (Figure 3.3).
In general, service flows in IEEE 802.16 are preprovisioned and setup of the service flows is initiated by the BS during SS initialization. However, service flows can also be dynamically established and immediately activated by either the BS or the SS. The SS typically initiates service flows only if there is a dynamically signaled connection, such as a switched virtual connection (SVC) from an ATM network. The establishment of service flows is performed through a three-way handshaking protocol in which the request for service flow establishment is responded to and the response acknowledged.

2. 
   MAC Functions for the Mesh Topology
   

In this section, we will focus on features and functions provided by the MAC layer protocol to support WiMAX mesh networks. Although the mesh topology has its distinct characteristics, some basic functions provided by the MAC protocol for the PMP topology are applicable in the mesh topology. This section will provide a general overview on the MAC protocol support to the mesh topology.

1. 
   Addressing and Connections
   

For addressing nodes in the local neighborhood, 8-bit link identifiers (link IDs) shall be used. Each node shall assign an ID for each link it has established with its neighbors. The link IDs are communicated during the link establishment process as neighboring nodes establish new links. The link ID is transmitted as part of the CID in the generic MAC header in unicast messages. The link

IDs shall be used in distributed scheduling to identify resource requests and grants. Since these messages are broadcast, the receiver nodes can determine the schedule using the transmitter’s node ID in the mesh subheader, and the link ID in the payload of the mesh mode schedule with distributed schedul- ing (MSH-DSCH) message. The connection ID in mesh mode is specified to convey broadcast/unicast, service parameters, and the link identification.

2.