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gement information base (MIB) for the media access control, PHY, and management procedures to make standard for network management of the IEEE 802.16 networks.

2.6.6 IEEE standard 802.16e-2005
The revision of the IEEE standard 802.16-2004 is IEEE standard 802.16e-2005. The extension defines the standard for mobile subscribers moving at vehicular speeds. It provides handover function among BSs. Although mobile functionalities are added into the amendment, fixed SSs can function with the IEEE Std 802.16e-2005 BSs. The band used in the amendment is limited to below 6 GHz licensed bands[21].

2.7 OPERATION MODES
The two modes of operation supported by IEEE 802.16 are, Point-to-Multipoint and Mesh mode.

2.7.1 PMP mode
Figure 2.3 shows a network working in PMP mode. An IEEE 802.16 link is handled through a BS and a sectorized antenna. Multiple sectors can be handled simultaneously. The traffic in PMP mode occurs only among the BS and the SSs. The signal could be sent to or from the BS. Downlink is the direction from the base station to the SSs. Conversely, the direction from a subscriber station to the base station is uplink. In a FDD scheme, uplink and downlink signal transmissions are simultaneous. In a TDD scheme, transmission time is divided into uplink and downlink periods. The downlink is usually broadcast. The SSs which have connections to an antenna sector by means of a given frequency channel receive the same signal transmission[12]. The uplink bandwidth to the BS is shared by the SSs. Depending on the class of service utilized, the IEEE Std 802.16 defines the bandwidth allocation and request mechanisms.

2.7.2 Mesh mode
The Mesh mode has been introduced in IEEE 802.16 in addition to PMP. It allows the IEEE 802.16 nodes to create mesh networks. In mesh network a communicating node connects to other nodes. If each node in a network directly connects to every other node, it is called a “fully meshed network”. Otherwise, it is a “partial meshed network”[11]. The mesh topology is shown in Figure 2.4.

Figure 2.5 shows a network working in Mesh mode. The traffic in Mesh mode can happen from a SS to another SS or other SSs. The Mesh mode allows signal to be routed through SSs, whereas the PMP mode allows signal to be routed only from the BS or to the BS. That means a node is not only a SS, but also a BS[11]. When a message is sent from the source, if a message does not arrive at its destination, the node forwards it to another neighbor. Selecting the next node depends on every node's routing table.

2.8 SUMMARY of IEEE 802.16

2.9 PROTOCOL LAYERS
802.16 IEEE standard consists of a protocol stack with well-defined interfaces. It works on two layers Common Medium Access Control Layer (MAC) of Data Link Layer and Physical Layer[5]. MAC layer consists of three sub-layers. Service Specific Convergence Sub-layer (MAC CS), the MAC Common Part Sub-layer (MAC CPS) and the privacy sub-layer.

The Service Specific Convergence Sub-layer is the sub-layer that permits CS to communicate with higher layers and converts higher-level data services to MAC layer service flows and connections. There are two types of CS sub-layer: ATM Convergence Sub-layer which is used for ATM networks and services, and packet Convergence Sub-layer which is used for packet services like Ethernet, Point to Point protocol (PPP), IPv4,本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。