The local area network is different from the TCP/IP protocol system used for external communication. It is a network distribution based on the traditional Ethernet (Ethernet) structure. In addition to using the TCP/IP protocol, it also involves many protocols.
In the local area network, the computers to find each other are not through IP, but through the MAC address of the network card. It is a set of unique identification numbers that are solidified during production. According to the protocol specification, when one computer needs to find another computer Time.
It must broadcast the IP of the target computer through the ARP protocol (Address Resolution Protocol) on the physical network. "Broadcast" is a data sending method that allows any computer to receive the data. After the computer receives the data, it will Determine if this message is sent to yourself, and if it is, it will return a response, where it will return its own address.
When the source computer receives a valid response, it knows the MAC address of the target computer and saves the result in the system's address buffer pool. The next time it transmits data, there is no need to send the broadcast again. This address buffer pool will Refresh and rebuild regularly to avoid data redundancy.
In fact, the sharing protocol stipulates that every computer in the local area network with file and printer sharing services must actively broadcast its own IP and corresponding MAC address to the network segment when it is started, and then a computer (usually a local area network) The first computer started in a working group within) assumes the role of receiving and storing these data.
This computer is called the "browsing master server". It is an extremely important computer in the working group. It is responsible for maintaining the browsing list in this working group and designating the master server list of other working groups. Computers and other computers visiting this workgroup provide browsing services, and its logo contains the \_MSBROWSE_ name field.
This is why we can see other computers in the network neighborhood. It is actually a browse list. Users can use "nbtstat -r" to view the list of NetBIOS names that have declared themselves on the browse master server.
The browse list records the resource description of the computers opened in the entire local area network. When we want to access the shared resources of another computer, the system actually sends a broadcast query to browse the main control server, and then browse the browse list provided by the main control server To "discover" the shared resources of the target computer.
But only knowing each other's addresses is not enough. A connected data link must be established between computers to work properly, which requires another basic protocol.
The NetBIOS (Network Basic Input Output System) protocol is a command set developed by IBM to provide network and other special functions to the local area network. Almost every local area network must work on this protocol. NetBIOS is equivalent to TCP/IP on the intranet. protocol.
The NetBEUI protocol (NetBIOS User Extended Interface Protocol) introduced later is an extension of the former. These protocols are the basic requirements to form a local area network. Finally, in order to establish a connection, the local area network also needs the TCP/IP protocol.
【definition】
In order to give a complete definition of LAN, two methods must be used: one is functional definition, and the other is technical definition. The former defines a LAN as a group of desktop computers and other devices that are not far apart from each other in physical addresses, and are interconnected in a way that allows users to communicate with each other and share computing resources such as printers and storage devices. This definition applies to LANs used in office environments, factories and research institutions. As far as the technical definition of LAN is concerned, it is defined as a computer interconnected by specific types of transmission media (such as cables, optical cables, and wireless media) and network adapters (also known as network cards) and monitored by a network operating system system.
The difference between the functional and technical definitions is obvious. The functional definition emphasizes external behavior and services; the technical definition emphasizes the material foundation and method of forming the LAN. The name of the local area network (LAN) itself implies the locality of the geographical scope of the network. Due to the limitations of a small geographic area, LANs generally have much higher transmission rates than wide area networks (WANs). For example, the transmission rate of LAN is 10Mb/s, the transmission rate of FDDI is 100Mb/s, while the backbone rate of WAN is only 64kbps or 2.048Mbps in China, and the upper limit rate for end users is usually 14.4kbps.
The topological structure of LAN is commonly used in bus type and ring, which is determined by the limited geographic range, and these two structures are rarely used in the wide area network environment. LAN also has a variety of features such as high reliability, easy expansion and contraction, easy management, and security. The local area network is generally owned by a department or unit. It is easy to construct, maintain, and expand, and the system is highly flexible. Its main features are:
The geographic coverage is relatively small, only in a relatively independent local area, such as a cluster of buildings.
Use specially laid transmission media for networking, high data transmission rate (10Mb/s～10Gb/s)
Short communication delay time and high reliability
The local area network can support multiple transmission media
There are many types of local area networks. If classified according to the transmission media used by the network, they can be divided into wired networks and wireless networks;
If classified according to the network topology, it can be divided into bus type, star type, ring type, tree type, mixed type, etc.;
If classified according to the access control method used by the transmission medium, it can be further divided into Ethernet, token ring network, FDDI network and wireless local area network.
Among them, Ethernet is currently the most commonly used local area network technology.
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