SP? Column = news & key = computer target = _bLANkclass = qqx_gjz> computer networks are often composed of many different types of network interconnection connection is made. Only if the number of computer networks are physically connected together, and can not communicate between them, then this "interconnection" has no practical significance. So often talk about "interconnect", he had already implied that these interconnected computers can communicate, that is, from functional and logic point of view, these computer networks have formed a large computer network, or known as the Internet, also referred to as the Internet, the Internet. The network connected to each other using some intermediate device (or intermediate systems), ISO terminology called relay (relay) system. Relay system according to the level where you can relay the following five systems: 1. The physical layer (that is often said that the first layer, the layer L1) relay system, the transponder (repeater). 2. Data link layer (the second layer, layer L2), the bridge or the bridge (bridge). 3. Network layer (third layer, the layer L3) relay system, the router (router). 4. Bridges and routers, a mixture of bridge device (brouter) both bridge and router functions. 5. In the network layer above the relay system, the gateway (gateway). When the relay system is the transponder, generally does not call it networking, since it is expanded to a network, but this is still a network. More complex high-level gateway, currently used less. Therefore, when a general discussion of the interconnection of networks that are interconnected with the switches and routers for the network. This article discusses the difference between switches and routers and. 2 switches and routers "Exchange" is the highest frequency of the network today, a word from the bridge to the route to the ATM until the phone system, no matter what occasion can be applied, not quite sure what is true in the end exchange. In fact, the word first appeared in the telephone exchange system, especially as to achieve two different voice signals between the telephone exchange, the completion of the work is telephone switching equipment. So, speaking from the intention to exchange only a technical concept that signals the completion of the entrance to the exit from the device forwarding. Therefore, and consistent with the definition as long as all equipment can be referred to as switching equipment. This shows that the "exchange" is a broad term meaning, when it is used to describe the second layer of data network equipment, the actual refers to a bridge device; and when it is used to describe the third layer of data network The device also refers to a routing device. We often say the Ethernet switch is actually a bridge technology, based on the second layer of multi-port network equipment, it is the data frames from one port to another arbitrary port forwarding to provide a low delay low-overhead acce ss. Thus, the switch should be an internal core of a switch fabric for communication between any two ports provide access to, or a rapid exchange of the bus, so that any port to receive data from the frames sent from other ports . In actual devices, switching matrix functions often by specialized chip (ASIC) to complete. In addition, the Ethernet switch to thinking in the design of an important assumption, namely, the core rate of exchange is very fast, which is usually a large flow of data is not to produce congestion, in other words, the ability to exchange information relative to the transfer infinite volume (to the contrary, ATM switches in the design idea is that the exchange capacity is relatively limited in terms of the amount of information transfer). Although the Ethernet switch is based on the second layer developed from the multi-port bridge, but after all, the exchange has richer features, so that not only the best way to get more bandwidth, but also to the netwo rk more manageable. The router is a network layer OSI protocol model of packet switching devices (or Network Layer relay equipment), the router's basic function is to data (IP packets) sent to the correct network, including: 1.IP packet forwarding, including datagram routing and delivery; 2. Subnet isolation, suppression broadcast storms; 3. To maintain routing tables with other routers to exchange routing information, which is the basis for forwarding IP packets. 4.IP data reported error handling and simple congestion control; 5. To realize the IP packet filtering and accounting. To scale for different networks, the focus of the role of the router is different. The trunk line, the router's main function is routing. Internet backbone routers, the network must know the path of the lower reach of all. This need to maintain large routing tables, and the connection state changes to the response as quickly as possible. Router failure will lead to serious problems of information t ransmission. In regional networks, the router's primary role is to network connectivity and routing, that is, the various grassroots network connecting the lower unit - campus network, also responsible for forwarding data between the lower network. Within the campus network, the router's main role is to separate the subnet. Early grass-roots Internet is LAN (LAN), in which all hosts in the same logical network. With the continuous expansion of network size, evolved into a high-speed LAN backbone and router connected to multiple subnets composed of campus. In which office a subnet logically independent, and the router is the only way to separate their devices, it is responsible for forwarding packets across subnets and broadcast isolation, on the border routers are responsible for the upper network. 3 second difference between switches and routers Traditional switches evolved from the bridge belongs to the second layer of the OSI data link layer device. It is based on MAC add ress address, select the routing table through the station, station for the establishment and maintenance of the switch automatically. Router belonging to the third layer of the OSI network layer device that IP address based addressing, routing protocols generated by the routing table. The greatest advantage is the quick switch, the switch only identify frames as MAC address, MAC address generated directly from the forwarding port selection algorithm is simple, easy ASIC implementation, therefore a high forward speed. However, the working mechanism of the switch has also brought problems.
access point vs router
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