The topological structure of LAN

Common LAN Topologies

The structure of star structure is one of the most widely used in local area network, which is used almost all in enterprise networks. Star Network is almost Ethernet (Ethernet) network dedicated, it is because the network of workstations node devices through a network of centralized devices (such as hubs or switches) connected together, each node is a star-shaped distribution named. This type of network currently uses the most transmission medium is twisted-pair, such as the common five types of lines, super five twisted pair and so on. The    basic characteristics of this topology network are as follows: (1) Easy to achieve: it is used by the transmission medium is generally used in general twisted pair, the transmission medium is relatively cheap, such as the current five types of genuine twisted-pair wire per meter is only about 1.5 yuan, and coaxial cable The cheapest also about 2.00 yuan a meter, fiber optic cable that is not to mention. This topology is mainly used in the IEEE 802.2, IEEE 802.3 standard Ethernet LAN, (2) node expansion, Mobile Convenience: node expansion only need to pull a line from a centralized device such as a hub or switch, and to move a node only need to transfer the corresponding node device to a new node, And will not be like the ring-type network "to take one of the global"; (3) easy to maintain; a node failure will not affect the connection of other nodes, can arbitrarily remove the fault node, (4) The use of broadcast information transmission mode: Any node send information in the entire network node can be received, which in the network has some hidden danger, However, this has little effect on the local area network; (5) Fast data transmission: This can be seen from the current 1000Mbps to 10G Ethernet access speed. In fact, its main characteristics far more than these, but because the latter we also want to specifically talk about various types of network access equipment, and the characteristics of the network is mainly subject to the characteristics of these devices to restrict, so other aspects of the characteristics of the corresponding network equipment in the later we will add.

ring-type structure of the network form of this structure is mainly used in the token network, the network structure of the devices are directly connected through the cable, and finally form a closed loop, the entire network sends the information is in this ring, usually referred to this kind of network as "Token Ring network." In     fact, in most cases, this topology of the network will not be all computers are really connected to the physical ring type, generally, the two ends of the ring is through an impedance match to achieve the ring closed, because in the actual network process due to geographical constraints inconvenient really do the two ends of the ring physical connection. The topology of the network has the following characteristics: (1) This network structure is generally only applicable to the IEEE 802.5 token network (Token Ring network), in such a network, "token" is transmitted in the ring-type connection in turn. The transmission medium used is generally coaxial cable. (2) This kind of network realization is also very simple, the investment is minimal. It can be seen from its network structure that the network, in addition to the workstations is the transmission medium-coaxial cable, as well as some connection equipment, there is no expensive node-focused equipment, such as hubs and switches. But also because of this, so this network can achieve the most simple function, only as a general file service mode, (3) faster transmission: In the token network allows 16Mbps transmission speed, it is much faster than ordinary 10Mbps ethernet. Of course, with the wide application of Ethernet and the development of Ethernet technology, the speed of Ethernet has also been greatly improved, the current generally can provide 100Mbps speed, far higher than 16Mbps. (4) Maintenance difficulties: From its network structure can be seen, the entire network of nodes are directly connected, so that any one node failure will cause the entire network interruption, paralysis, maintenance is very inconvenient. On the other hand because the coaxial cable is the use of pin-type contact, it is very easy to cause poor contact, network interruption, and this is very difficult to find, this is believed to maintain the network of people will have deep experience. (5) Poor expansion performance: It is also because of its ring structure, decided that its expansion performance is far better than the star structure, if you want to add or move nodes, you must interrupt the entire network, at both ends of the ring as a good connector to connect.

3. Total line structure all the devices in this network topology are directly connected to the bus, the medium used is also coaxial cable (including coarse and thin cable), but now also use the optical cable as the total line transmission medium, such as the following we will talk about the ATM network, Cable The network used in modem is the total linear network structure.     This structure has the following aspects of the characteristics: (1) Low-cost network: From the structure can not need additional interconnection equipment, is directly connected through a bus, so the network cost is low; (2) This kind of networks because each node is common bus bandwidth, Therefore, the transmission speed will decrease with the increase of the number of users of the Access network; (3) network user expansion is more flexible: need to expand the user only need to add a connector, but the amount of users can connect limited; (4) Easy to maintain: failure of a single node does not affect the normal communication of the whole network. However, if the bus is broken, the entire network or the corresponding backbone segment is broken. (5) The disadvantage of this network topology is that only one end user can send the data at a time, and the other end users must wait to get the right to send.

 
 4.    Hybrid topology    This network topology is a network structure which is combined with the network of the star structure and the total linetype structure, which can satisfy the expansion of the large network, and solve the limitation of the Star-type network in the transmission distance. At the same time, it solves the limit of the number of connected users in the total Linetype network.    This network topology also takes into account the advantages of the star network and the total Linetype network, which has been compensated for in some shortcomings. This network topology is mainly used in large-size local area networks, if a unit has several geographically distributed farther (of course, the same cell), if the whole company's local area network by the Star-type network, because the star-type network transmission medium-twisted pair of single-segment transmission distance (100m) is difficult to succeed , it is very difficult to take the company's computer network scale if the total linear structure is used for wiring. In combination with these two topologies, we adopt twisted-pair star structure on the same floor, and we adopt the total linear structure of coaxial cable on different floors, and we must adopt bus type between building and building, and the transmission medium depends on the distance between the building and the building. If the distance is closer (within 500m) we can use coarse coaxial cable as transmission medium, if a thin coaxial cable can be used as transmission medium within 180m. However, if more than 500m we only use optical cable or thick cable and repeater to meet. This type of cabling is our common cabling method. The main features of this topology are as follows: (1) The application is quite extensive: this is mainly because it solves the shortage of the star and the general linear topological structure, satisfies the actual demand of the large company network, and (2) the extension is quite flexible: this is mainly the advantage of inheriting the star topology structure. However, due to the use of broadcast messaging, the length of the bus and the number of nodes will also be limited, but there is no big problem in the local area network, (3) the network rate with the same total linetype networks will decrease with the increase of the user's weakness; (4) difficult to maintain, This is mainly constrained by the topological structure of the general linear network, if the bus is broken, the entire network will be paralyzed, but if the branch network segment has failed, it still does not affect the normal operation of the entire network. Another whole network is very complex, maintenance is not easy, (5) faster: Because its backbone of the use of high-speed coaxial cable or optical cable, so the entire network in the speed should not be too much restrictions. 

In general, enterprises to build a LAN using star structure, if the enterprise floor and floor need to build LAN, then you have to adopt a hybrid topology (star structure and the total line structure).

The topological structure of LAN