Network Topology

Topology this noun borrowed from geometry. Network topology is network shapes, or is it in physical connectivity. Constitute the topology of the network has a lot of kinds. Network topology structure refers to various equipment with transmission media interconnection of physical layout, is in what manner put the computer on the network equipment joined up. Situs given network server and workstations network configuration and mutual connection, its structure is mainly have star structure, the annular structure, bus structure, distributed structure, tree structure, mesh structure, cellular structure, etc.

Star topology structure

Star structure is one of the oldest connection mode, everybody everyday usage of telephone belongs to this structure. Star structure is to point to each workstations to star way connected into the nets. The network has a central node, other nodes (workstation, server) are directly connected with the central node, the structure with the central node is the center, so called star topology structure is one of the oldest connection mode, everybody everyday usage of telephone belongs to this structure. Star structure is to point to each workstations to star way connected into the nets. The network has a central node, other nodes (workstation, server) are directly connected with the central node, the structure with the central node is the center, so called centralized network. Star topology structure facilitates concentration control, because the communication between the end users must pass formulates. Because this one characteristic, also brought easy maintenance and safety, etc. End users equipment for failure when stop also will not affect the other end users communications. Meanwhile star topology of network delay time is lesser, transmission error is relatively low. But this kind of structure is very adverse point is the center system must have high reliability, because center system once damaged, the whole system tends paralysis. This center system usually adopt dual machine thermal back-up, in order to improve the system reliability.

In star topology structure, network of each node through point-to-point way connected to a central node (also called the central transfer station, general is a hub or switch on, by the central node to destination node transmit information. The central node execution centralized control strategy, hence the central communication nodes are quite complex and burden much heavier than each node. In any two nodes in star nets should undertake communication must pass the central node control.

Existing data processing and voice communication of information WangDa used more star nets, currently popular PBX PBX (Branch Exchange), namely to telephone switchboard is star nets topological structure of typical examples. It was in a units inside for comprehensive voice and data exchange information channel, the workstation can also provide voice mail and telephone meetings and other business, is an important branch of LAN.

In any two nodes in star nets should undertake communication must pass the central node control. Therefore, the main function of central node has 3: when asked to communication site issued communication request, controller to check whether central transfer station have free access, called the equipment is free, to decide whether to establish both physical connections, At least two equipment communication process to maintain this pathway, When communicating finished or not success requirements, the central station take out stitches can be dismantled the above connecting passage.

The central node with multi-motor connection, the line more, for facilitates concentration attachment, and currently used more a become hubs (on) or exchange equipment hardware as a central node. At present general network environment has been designed to star topology. Star net is currently extensively and preferred the use of network topology design one. 

Centralized network

This structure facilitates concentration control, because the communication between the end users must pass formulates. Because this one characteristic, also brought easy maintenance and safety, etc. End users equipment for failure when stop also will not affect the other end users communications. At the same time it network delay time is lesser, transmission error is relatively low. But this kind of structure is very adverse point is the center system must have high reliability, because center system once damaged, the whole system tends paralysis. This center system usually adopt dual machine thermal back-up, in order to improve the system reliability.

The annular network topology

The annular structure in LAN used in more. This structure of transmission media from one end users to another end users, until all the end users connect annulus. Data in one direction only in PLL transmission between each node, information from one node to another node. This structure is obvious eliminates end users while communicating to center system dependence.

Round structure features are: each end users with two neighboring end users connected, thus exist point-to-point link, but always with unidirectional way, so they have operating the upstream end users and downstream end users said, Information flow in the net is along the fixed direction of flow of, only two nodes on a path that is simplified the routing control; Loop at each node is bootstrap control, so the control software simple; Because information serially in PLL is through each node, when ring node overmuch, certainly will influence the information network transmission rate, make the response time of the extension, If the loop is closed, do not facilitate expansion, Reliability is low, a node fault, which will result in hyper paralysis, Maintenance of branch node difficult, fault locating more difficult. 

Bus-control topological structure

The bus is usually much information transmission using baseband form serial transmission, every node on the network interface board hardware have received or sent function, receiver bus serial information and translated into parallel information to PC workstation, Transmitter is to convert serial parallel information information broadcast to the bus, the bus to send information to the destination address of the nodal interface autogeneration timeliness, this node of the receiver will receive messages. As a result of each node is passed between cable directly connection, so bus-control topological structure required by a cable length is the smallest, but the bus only certain load ability, because this bus length and have certain restriction, a bus connect only a certain number of nodes.

Because of all the node sharing a common transmission lines, so one can only by a equipment transmission. Need some form of access control strategy, to decide which one standing next may send. Usually taken distributed control strategy. Send a message when transmitting station will be divided into groups. Then one at a time in order to send these groupings. Sometimes must with other standing to the grouping of alternately in medium transmission. When the group after stations, objective stand will identify packet address. Then copy these grouping content. This topology lightened the burden of network communication processing, it is just a passive transmission medium, and communication in various stations handle distribution.

In the bus ends are connected with the knot device (or terminal verifier), mainly with bus impedance matching, maximum absorption sender department of energy to avoid signal reflected back to bus to produce needless interference.

Bus structure is using the same medium or cable connection all end users a way, that is to say, the physical media connected end users by all equipment sharing, each workstation equal status, no central node control, public bus information more using baseband form serial transmission, its delivery direction always from send information node began to spread ends, as radio emission the same information, so say again AnBoShi computer network. Each node in accept information were address checked to see if with their own workstation autogeneration, conform to the information on the net is receiving.

Use this construction must solve a problem is to ensure that end users use media while sending data cannot appear conflict. In point-to-point link configuration, this is quite simple. If this road links are half-duplex operation, simply use very simple mechanism and can ensure the two end users work by turns. In a little to multi-point manner, the line of access to determine the inquire based on controlling. However, in LAN conditions, due to all data stations are equal, cannot take the mechanism. To this, studied in a bus sharing type network media used access methods: with collision detection of protected reliably against detective multi-channel access, carrier English abbreviated to CSMA/CD.

This structure with low cost, data end users access flexible, site or a end users failure does not affect other sites or end user communication advantages. Defect is one can only one end users send data, the other end users must wait to get send power; Media access access mechanism is relatively complicated, Maintain difficult, branch node troubleshooting difficult. Despite such some shortcomings, but because wiring requirement is simple, expansion of easy, end users invalidation, add do not affect hyper work, so is LAN technology in the most common use of a.

Distributed topological structure

The distributed structure of the network is distributed in different locations computer through circuit interconnecting a web form. The distributed structure of the network has the following characteristics: due to the distributed control, even if the whole network of some local malfunction, also won't affect entire network operation, thus has the very high reliability, Nets choice of path shortest path algorithm, so online delay time less, transmission rate is high, but controlling complex. Each node all can be established directly between data link, information flow is the shortest, Facilitate network-wide security resources sharing. Faults for connection with cable length, cost is high, Network management software complex. Message packet switching, route choice, flow control complex. In general LAN not use this structure.

Tree topology structure

Tree structure is the hierarchical centrally controlled type network, and star than its total length of short communication lines, low cost, easy to extend node, looking for the path is more convenient, but besides leaf nodes and its connected lines, any node or its connected line fault will make the system affected.

Mesh topology structure

Mesh topology mainly refers to the Internet through each node connected transmission line, and each node with at least two other nodes connected. Mesh topology structure has higher reliability, but its structure is complex, realize rise higher cost, not easy to maintain and manage, not often used in LAN!

Multiple subnet or more network connecting up reticular topologies. In a subnet, hubs, Repeaters, will more device connected, and a bridge, routers and gateways will connected subnet. According to the network hardware is different, there are three main mesh topology:

Mesh network: in a large area, with radio communications links a large network, mesh network is the best topological structure. Through the routers and routers connected, can let the quickest route choice a network data transmission, as shown in figure 5-4 shows.

Backbone: through a bridge and router make different subnet or LAN connect to form a single bus or ring type topology, the nets usually adopts the fiber main lines.

Stellate connected network: use some called super hub equipment will network connection rise, because star structure characteristics, any place in network fault can be easy to find and repair

Cellular topological structure

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

Mixed topologies

The two or several network topology structure of mixed together constitute a network topology is called the mixed mode topology structure (also some called heterozygous type structure).

This kind of network topology structure consists of star structure and bus-control structure of network together in the network structure, such topology structure which can better satisfy large network development, solve star network in the transmission distance on limitations, and at the same time to solve the bus-control network in connecting the number of users limit. This kind of network topology for both the star nets and bus-control the advantage of network, in faults got certain remedy.

This kind of network topology is mainly used for larger LAN, if a unit owns several geographically distribution is more far (certainly is in the same village), if the pure with star nets to group the whole company LAN, and by star network transmission medium - twisted-pair single segment the transmission distance (100m) limit to succeed, If simple adopts bus-control structure to wiring is hard to bear the company's computer network size needs. Combining the two topology, in the same building floor we adopt twisted-pair star/structure, and different floor we over coaxial cable bus-control structure, and in between building and building we must also adopts bus-control, transmission medium of course should inspect the distance between the building and building, if closer distances (within 500m) we can use thick coaxial cable for transmission medium, if in 180m within still can use thin coaxial cable for transmission medium. But if more than 500m we only through the cable or thick cable add Repeaters to meet. This wiring way is our common integrated wiring way.

The radio communication topological structure

Transmission system except coaxial cable, optical fiber twisted-pair, and outside, still have a kind of means is don't use wire, it is the radio communication, wireless communication using electromagnetic wave or light to transmit information, use it without laying cable can put the network connecting. The radio communication include two unique network: mobile Internet and wireless LAN network. Using LAN nets, machine can be connected through a transmitter and receiver, Using YiDongWang, the machines can through cellular communication system, the communication system connected by radio communication departments to provide.

The structure of the Ethernet network can be from the server, physical, routers, workstations, operating terminal through hub star formation structure constitute LAN.

Internet cafe network topology structure

Internet cafe network topology structure: net cafe USES is the star topology of network.

Use features

Internet bar the burgeoning industry, leading many business development, Internet cafes router as the key access devices, Internet cafes must be very suitable for Internet cafe using the features as follows:

General net cafe machine number little criterion more than 100 sets, too much is hundreds of ramps, and operators to access bandwidth in many places are not big, need cost-effective use. Internet cafe internal use have game, browse, chatting, video, download, etc. One online game and the real-time chat program packets are small, compare in network congestion conditions must have priority through permissions, will not lag.

Different toll partition using different network speed. Now basically points in several different net cafe charges, this time should not only in price, service content on different in network access speed is due also different. So will a access line was partitioned into several levels are reasonable.

The P2P software restricted or banned. The P2P software became network bandwidth of cutthroat, not only take up large bandwidth, and consumed a lot of access thread. Should the access layer directly on of this software to restrict or prohibit.

Intelligent management. Internet cafes such service industry, and emphasize the humanized service. While in network service structure

On, intelligent management is humanization embodiment. For instance in network not busy circumstance, should cancel on client using the network bandwidth limitations, achieve network bandwidth maximize. While in network busy cases, and should start limits, thus make sure everyone can use to the largest network bandwidth. And of course more humanized service functions. Network security requires high, Since each machine operator often changes, therefore, in some attack is inevitable, access devices have a strong ability to fight dozen, meanwhile needs data isolation function.

Need to compare strong management and monitoring of the function. Can find out from many machines not healthy. From the sea in the same packet inside out a specified object. Internet is not fixed, have problems troubleshooting, rather than by frequent restart your device way. Equipment real-time network management and monitoring function to healthy and stable operation is very important.

Throughput, handling ability and stability requirement high, Internet cafe is a commercial operation environment, these are the basic requirements.

Many lines access and expand bandwidth. Because the bandwidth limitations, ADSL Internet cafes in some areas that require multiple lines access, so also needs to have balanced load and line redundancy backup ability.

Details of the implementation

1, the setting of the packet level of network game, prioritizing the packet forwarding!

2, according to procedures for bandwidth delaminated management, such as QQ program can only be occupied by the bandwidth for 2M bandwidth, IE browser can only occupy 3M bandwidth.

3, on each machine the bandwidth and thread count limit, if the network not busy is no limit.

4, the computer for ordinary Internet network occupy limit, each machine machine bandwidth point with no more than 30KBps/s. 5, to the P2P software total bandwidth limitations, P2P total bandwidth cannot exceed 100KBps/s. And single P2P process cannot exceed 20.

6, for different partitions the Vlan Settings.

7, caused by using the two-lane access, set the objectives tactics routing, according to the customer visit target automatic selection access routes. And limit the hot backup, if a certain line abnormal disconnect, then all data forwarding to another line. Until returned to normal.

8 and all machine a ARP binding. Eliminate the connection ARP deception.

9, configure a firewall, can resist general network attack.

10 and opens the current connection state list, can view all machines with which currently in target connection.

11, if the customer visit designated website, will go directly to the Internet cafe internal web site. Or prohibit visit those designated website.

12 and other common Settings and customer requirements set