TOPOLOGY

TOPOLOGY is an independent research and the size and distance of the geometry characteristic method. Network topology is by the network node equipment and communication media constitute network structure. In choosing topology structure, main consideration factors are relatively difficult installation easy degree, the degree of difficulty to reconfigure the relative, maintenance degree of difficulty, communication medium is at fault, affected equipment.

A basic terms.

1. The node

Node is network units. Network unit is network system in various data processing equipment, data communication control equipment and data terminal equipment.

Node is divided into: transfer nodes, its role is to support network connection, it through the communication lines connecting and transmit information;

Visit node, it is the exchange of information source point and goals.

2. Link

Link is attachment between two nodes. Link points "physical link" and "logical link" two kinds, the former refers to the actual existence of communication, the latter refers to the attachment in logic of network access role. Link capacity refers to each link in unit time can accept the biggest information.

3. Pathways

Access the node to send information from the receiving the information of a string of nodes between nodes and link. In other words, it is a series of cross communication network and the node to establish the link node.

2. Common network topology structure

1. Star structure

The advantages of star structure is simple in structure, easy, control relatively simple arrangement. Its defect is of centralized control, main node too heavy a load, reliability is low, utilization rate is low to communications lines. A star LAN can be hidden in another star LAN and form a tree or hierarchical network topology structure. Relative to other network topology for installation is more difficult, than any other network topology use. The cable Easy to reconfigure, need to remove, add or change the connection, a port hub for network reconfigured. Because all data on star network the center equipment, and in the center equipment pooling, star topology maintenance be easy. The fault influence equipment less, better able to deal with.

2. The bus structure

Bus structure is more widely adopted a way that it will all access computers have access to a communications line, to prevent signal reflection, general at both ends even have an end device bus line impedance matching, bus structure is the advantage of channel utilization, simple structure, high price is relatively cheap. Defect is the same time can only have two network node mutual communication, network extensions distance is limited, network limited number for node. On a bus as long as there is one point linking problem, it will affect appear normal operation of the whole network. Currently in LAN used more such structure.

Bus topology network usually short cables (branch cable) with cable joint connected to a long cable (main) up. Bus topology network is usually use T BNC connector will computer connected to coaxial cable directly trunk. The backbone to an end device matching ends even line impedance. Bus topology network is relatively easy to install, just laying main cable, than other topological structure of the cable to use less. Configuration is simple, easy to add or delete node, but when acceptable branch points to limit, it must to laying main cable. Relatively maintenance difficulties, because in the exclusion of medium fault, will isolate to a certain segment of the mistake. The fault of the large range of influence equipment. Star on a node is the center of structure of the processing system, various types of access machine with the center node has both physical link directly connected.

3. The annular structure

The annular structure is the platform of computer networking with various communication lines connected into a closed loop.

In the annular structure networks, according to information flow, or fixed direction clockwise or anti-clockwise direction. The advantages of annular structure is a communication and information in the biggest transmission network transmission delay is fixed; Each online node with other two node has only physical link direct interconnection, therefore, transmission control mechanism is simple, and strong real-time property. Defect is a node malfunction may terminate hyper poor run, so reliability. In order to overcome poor reliability problems, some network using a self-healing function is? Structure, once a node does not work, automatic switch to another loop work. At this time, the network topology and should be hyper adjust access control mechanism, and therefore is more complicated. The annular topology is a point-to-point ring type structure. Each device are directly connected to ring, or through an interface equipment and branch cable connected to ring. After initial installation, the annular topology network is simple. With online node, reconfiguring the increase the difficulty of to ring, also increased the maximum length and ring equipment limited is the total number. Can easily find fault point of cable. The fault influence in the range, equipment of monocylic system appear on any error, can affect all online equipment.

4. Tree structure

Tree structure is actually a kind of star structure with original deformation, it will link directly connected node alone by multi-level processing host was graded connection.

This structure and star structure of the lower than the cost communication lines, but increased network complexity. Network the lowest layer node and its attachment outside, any node or cords are where the fault affecting its normal work. The branch network

5. Reticulation

Mesh structure is divided into full connection mesh and incomplete connection mesh two forms. The connection, each node reticular and net other nodes are links. Not completely connected nets, two nodes is not necessarily direct links, the communication between them, relying on other nodes through. This is the advantage of network path between the nodes, collision and jams can decrease greatly, partial failure will not affect the whole network of normal work, high reliability; Network expansion and host access more flexible, simple. But this network, set up the complex relationship is not easy, network control mechanism complex. Wan generally exhaustless whole connection network structures.

6. Honeycomb topologies

Cellular topology structure is used in the structure of the wireless local area network. It with wireless transmission medium (microwave, satellite, infrared, etc.) for point-to-point and multicast characteristic, is a kind of wireless networks, suitable for urban nets, campus network, enterprise nets.