Shulou(Shulou.com)06/02 Report--

Today, I will talk to you about the topology of the computer network, which may not be well understood by many people. in order to make you understand better, the editor has summarized the following for you. I hope you can get something according to this article.

According to the topological structure, the computer network is divided into star topology, bus topology, ring topology, tree topology, hybrid topology, network topology and switching power supply topology. Among them, the star network topology is the most widely used network topology.

Correlation

The topological structure of computer network refers to the physical composition mode of nodes and lines formed by computers or devices on the network and transmission media. There are two types of nodes in the network: one is the transfer node that converts and exchanges information, including node switches, hubs and terminal controllers, and the other is access nodes, including computer hosts and terminals. Lines represent a variety of transmission media, both tangible and invisible.

Specific types:

Star topology

The star topology consists of a central node and each site connected to the central node through a point-to-point communication link. The central node implements the centralized communication control strategy, so the central node is very complex, and the communication processing burden of each site is very small. The switching methods adopted in star networks are circuit switching and message switching, especially circuit switching. Once a channel connection is established, this structure can transfer data between two connected sites without delay. The popular private exchange PBX (Private Branch exchange) is a typical example of a star topology.

Advantages of star topology

The main results are as follows: (1) it has the advantages of simple structure, convenient connection, relatively easy management and maintenance, and strong expansibility.

(2) the network delay time is small and the transmission error is low.

(3) multiple transmission media are supported in the same network segment, and the network will not be paralyzed easily unless the central node fails.

(4) each node is directly connected to the central node, the fault is easy to detect and isolate, and the faulty node can be eliminated easily.

Therefore, the star network topology is the most widely used network topology.

Shortcomings of star topology

(1) the cost of installation and maintenance is high

(2) the ability to share resources is poor.

(3) A communication line is only used by the central node and edge node on the line, and the utilization rate of the communication line is not high.

(4) the demand for the central node is quite high. Once the central node fails, the whole network will be paralyzed.

Star topology is widely used in the situation where the intelligence of the network is concentrated in the central node. From the trend, the development of computers has developed from centralized host systems to a large number of powerful microcomputers and workstations. In this situation, the use of traditional star topology will be reduced.

Bus topology

The bus topology uses a channel as the transmission medium, and all stations are directly connected to this common transmission medium through the corresponding hardware interface, which is called the bus. The signal sent by any station propagates along the transmission medium and can be received by all other stations.

Because all stations share a common transmission channel, only one device can transmit signals at a time. When a distributed control strategy is usually used to determine which station can send o, the sending station divides the message into packets, and then sends these packets one by one, sometimes alternately transmitting on the media with the packets from other stations. When the packet passes through each station, the destination station will identify the destination address carried by the packet, and then copy the contents of these packets.

Advantages of bus topology

The main results are as follows: (1) the bus structure requires a small number of cables, short cable length, and easy to wiring and maintenance.

(2) the bus structure is simple, and it works as a meta-source, so it has high reliability. The transmission rate is high and can reach 1~100Mbps.

(3) it is easy to expand, it is convenient to increase or decrease the number of users, the structure is simple, the networking is easy, and the network expansion is convenient.

(4) multiple nodes share one transmission channel, and the channel utilization is high.

Disadvantages of bus topology

The main results are as follows: (1) the transmission distance of the bus is limited and the communication range is limited.

(2) it is difficult to diagnose and isolate faults.

(3) the distributed protocol can not guarantee the timely transmission of information and does not have real-time function. The site must be intelligent and have media access control capabilities, thus increasing the hardware and software overhead of the site.

Ring topology

In the ring topology, each node is connected to an end-to-end closed loop communication line through the loop interface, and any node on the loop can request to send information. Once the request is approved, a message can be sent to the loop. Data in a ring network can be transmitted either unidirectionally or bidirectionally. Because the loop is common, the information sent by a node must pass through all the loop interfaces in the loop. when the destination address in the information flow matches the address of a node on the ring, the information is received by the node's loop interface, and then the information continues to flow to the next loop interface, all the way back to the loop interface node that sent the information.

Advantages of ring topology

(1) the cable length is short. The cable length required by a ring topology network is similar to that of a bus topology network, but much shorter than that of a star topology network.

(2) when adding or decreasing workstations, only a simple connection operation is needed.

(3) Optical fiber can be used. The transmission rate of optical fiber is very high, so it is very suitable for unidirectional transmission of ring topology.

Disadvantages of ring topology

(1) the failure of nodes will cause the failure of the whole network. This is because the data on the ring is transmitted through every node connected to the ring, and once a node in the ring fails, it will cause the failure of the whole network.

(2) it is difficult to detect faults. This is similar to the bus topology, because it is not centralized control, fault detection needs to be carried out in each node on the network, so it is not very easy.

(3) the media access control protocols of ring topology adopt the way of token passing, and when the load is very light, the channel utilization is relatively low.

Tree topology

The tree topology can be thought of as a multi-level star structure, but this multi-level star structure is distributed in a triangle from top to bottom, just like a tree, with fewer branches at the top, more in the middle, and the most at the bottom. The lowest end of the tree is equivalent to the edge layer of the network, the middle part of the tree is equivalent to the aggregation layer of the network, and the top of the tree is equivalent to the core layer of the network. It adopts hierarchical centralized control mode, its transmission medium can have multiple branches, but does not form a closed loop, and each communication line must support two-way transmission.

Advantages of tree topology

(1) easy to expand. This structure can extend many branches and sub-branches, and these new nodes and branches can be easily added to the network.

(2) Fault isolation is easy. If the node or line of a branch fails, it is easy to isolate the fault branch from the whole system.

Disadvantages of tree topology

Each node is too dependent on the root, if the root fails, the whole network can not work properly. From this point of view, the reliability of the tree topology is somewhat similar to that of the star topology.

Hybrid topology

Hybrid topology is a topology that combines two single topologies and takes their advantages.

One is the "star-ring" topology formed by the mixture of star topology and ring topology, and the other is the "star-total" topology which is composed of star topology and bus topology.

The two hybrid structures have something in common, and if the two endpoints of the bus topology are connected together, it becomes a ring topology.

In the hybrid topology, the aggregation layer devices form a ring or bus topology, and the aggregation layer devices and access layer devices form a star topology.

Advantages of hybrid topology

(1) it is convenient for fault diagnosis and isolation. Once the network fails, as long as it is diagnosed which network device is faulty, the network device can be isolated from the whole network.

(2) easy to expand. When you want to expand users, you can add new network devices, or you can leave some spare interfaces in each network device that can be plugged into the new site at design time.

(3) easy to install. The main link of the network only needs to connect the aggregation layer devices, and then connect the aggregation layer devices and access layer devices through the branch link.

Disadvantages of hybrid topology

The main contents are as follows: (1) it is necessary to select intelligent network equipment to realize automatic network fault diagnosis and fault node isolation, and the cost of network construction is relatively high.

(2) like the star topology, the cable installation length from the aggregation layer equipment to the access layer equipment will increase more.

Network topology

Network topology. This structure has been widely used in the wide area network, and its advantage is that it is not affected by bottleneck and failure problems. Because there are many paths connected between nodes, we can choose the appropriate route for the transmission of data flow, so as to bypass the failed components or overbusy nodes. Although this structure is complex, the cost is high, and the network protocol that provides the above functions is also complex, it is still welcomed by users because of its high reliability.

One application of network topology is in the BGP protocol. In order to ensure the connectivity between IBGP peers, it is necessary to establish a fully connected relationship between IBGP peers, that is, mesh networks. Assuming that there are n routers inside an AS, the number of IBGP connections that should be established is n (NMUI 1) / 2.

Advantages of network topology

The main results are as follows: (1) there are many paths between nodes, and the collision and blocking are reduced.

(2) the local failure does not affect the whole network and has high reliability.

Disadvantages of network topology

The main results are as follows: (1) the network relationship is complex, it is difficult to build the network and it is not easy to expand.

(2) the network control mechanism is complex, so routing algorithm and flow control mechanism must be adopted.

Switching power supply topology

With the continuous development and improvement of PWM technology, switching power supply has been widely used because of its high cost performance. There are many circuit topologies of switching power supply, and the commonly used circuit topologies are push-pull, full-bridge, half-bridge, single-ended forward and single-ended flyback. Among them, in the half-bridge circuit, the primary transformer flows through the current in the whole cycle, the magnetic core is fully utilized, and there is no problem of magnetic bias, the voltage resistance of the power switch used is low, and the saturation voltage drop of the switch tube is reduced to a minimum. the requirement for input filter capacitor voltage is also low. Due to the above reasons, the half-bridge converter is widely used in the design of high-frequency switching power supply.

There are about 14 basic topologies commonly used in switching power supplies.

Each topology has its own characteristics and applicable situations. Some topologies are suitable for off-line (grid-powered) AC/DC converters. Some of them are suitable for low power output (~ 200V) or multiple groups (more than 4 to 5 groups); some use fewer devices at the same output power or have a good compromise between the number of devices and reliability. Small input / output ripple and noise are also often considered in topology selection.

Some topologies are more suitable for DC/DC converters. The choice also depends on high power or low power, high voltage output or low voltage output, and whether to require as few devices as possible, and so on. In addition, some topologies have their own defects and require complex circuits that are difficult to quantitatively analyze in order to work.

Therefore, in order to choose the topology properly, it is very important to be familiar with the advantages and disadvantages and the scope of application of different topologies. The wrong choice will make the power design doomed to failure in the first place.

Common topologies of switching power supplies:

Buck switching regulator topology, boost switching regulator topology, reverse polarity switching regulator topology, push-pull topology, forward converter topology, double-ended forward converter topology, interleaving forward converter topology, half-bridge converter topology, full-bridge converter topology, flyback converter topology, current-mode topology and current-fed topology, SCR resonant topology, CUK converter topology

A summary of various topologies of switching power supply first gives six basic DC/DC converter topologies

Buck,boost,buck-boost,cuk,zeta,sepic converter in turn

Disadvantages of tree topology:

Each node is too dependent on the root.

After reading the above, do you have any further understanding of the topology of the computer network? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.