3.2 Mesh network
Formally, a Mesh network is a type of network topology in IEEE 802.16 OFDM mode, and its physical layer is OFDM. Therefore, the differences Mesh6сети with considered modes are manifested not only and not so much on a physical level. The main difference Mesh6сети from considered still architecture "Toccata" - that if in the latter case, the speaker can only communicate with the BS, Mesh6сети interaction can take place directly between the speakers. Because network IEEE 802.16 standard is designed to work with a wide frequency channels, Mesh6сети entered standard not to create peer-to-peer local area networks - for this is the standards group IEEE 802.11. The reason given is a necessary tool for building a broadband network in which traffic can be transmitted via a chain of several stations, thereby eliminating the problem of transmission in the absence of direct visibility. Respectively, and of all the mechanisms of governance, in principle allowing you to build a decentralized distributed network, all focused on a tree-like architecture, with a dedicated base station (root node) and the dominant streams of BS-AC. In Mesh6сети all stations (nodes) are formally equivalent. However, almost always traffic throughout the Mesh network with the external environment occurs through one particular node (Fig.7). Such a node called the base station Mesh network, it is necessary to control Mesh network functions. While access control can take place either on the basis of the mechanism of distributed control or centralized way, under control of the BS. Different combinations of these methods.
A basic concept in the Mesh network are neighbors. Under the neighbors understand a particular node, all nodes that can establish a direct connection. They all form a neighborhood environment. Nodes associated with the specified node via the neighbor nodes, called neighbors of second order. Can be neighbors of the third order, etc.
In the Mesh network has no concept of ascending/descending channels. All communication is through frames. Stations transmit messages either within their allotted time intervals (in accordance with the previous channel assignment), or access channels with arbitrary (random) manner. Each node has a unique 486 bit MAC address. In addition, to identify within the Mesh network stations assigned 166 bit network identifier.
Figure 12 - example of a Mesh network
The allocation of channel resources in the Mesh network can be centralized and decentralized (distributed). In turn, the decentralized allocation is coordinated with the BS and not coordinated. The decentralized allocation of resources implies that the distribution occurs within one group of neighbors (i.e., between stations can directly communicate with each other). At coordinated decentralized distribution nodes communicate among themselves by special message control the distribution (distributed scheduling - DSCH).
Coordination is that the period of issuance of such messages each station are determined and known to her neighbors. Coordinated DSCH messages are transmitted in subcateg precedence constraints of access specified in the network descriptor intervals. Uncoordinated DSCH messages are transmitted in the subframe of data. DSCH messages are requests to receive channel resource and response messages with the provision (confirmation) of available resource (time slot per subframe data).
Resource is provided to the neighbor for a specific connection. Centralized allocation of resources implies a tree-like network topology with the BS at the top. It is implemented through two types of messages - centralized configuration CSCF and Central planning CSCH. These control messages are placed at the beginning of the subframe chart management access. Using message Central planning CSCH, each node determines the need for traffic to its child nodes (i.e., traffic from (to) BC passes through the node), and reports their needs to the parent node until the BS. After analyzing the need, the BS sends a message CSCH, informing each node on its allocated bandwidth (in bps) in the ascending and descending directions. Based on these data, each node asks himself (or assigns) the location of the packet in the subframe of data from (to) of its neighboring nodes through messages decentralized planning DSCH.
Message to centrally configure CSCF BS are formed and transmitted over the network to inform all nodes about the current state. CSCF includes information such as the number of available logical channels and their list, the list of nodes in the network indicating the number of child nodes for each of them, as well as profiles of the ascending/descending packages for each child node.