Local area network (LAN), compared with wide area network, mainly refers to the computer interconnection network in a small area. This "small scope" can be a family, a school, a company, or a government department.
The public network and external network often mentioned in BT, namely wide area network (WAN); BT usually refers to private network and intranet, that is, local area network (LAN).
Every computer (or other network device) on a WAN has one or more WAN IP addresses (or IP addresses of public networks and extranets). Generally, you can only apply for WAN IP address after paying at ISP, and WAN IP address cannot be duplicate. Each computer (or other network equipment) on the local area network has one or more local area network IP addresses (or private network and intranet IP addresses), which are distributed within the local area network, and the IP addresses of different local area networks can be repeated without affecting each other.
The data exchange between WAN (wide area network, public network, extranet) and LAN (local area network, private network, intranet) computers should be carried out through NAT (Network Address Translation) of routers or gateways. Generally speaking, routers or gateways will not block external connection requests initiated by computers in local area networks (LAN, private network and intranet), but routers or gateways will block connection requests initiated by computers in local area networks in most cases.
Complete the explanation
Local area network (LAN) refers to a network system with limited transmission distance and high transmission speed for the purpose of sharing network resources. Features:
1. The distribution range is limited.
2. High communication bandwidth and high data transmission rate.
3. Reliable data transmission and low error rate.
4. Coaxial cable or twisted pair is usually used as transmission medium.
5. The topological structure is simple and clear.
6. The control of the network is usually distributed.
7. The network is owned and used by an organization.
MAN is a large-scale high-speed network between LAN and WAN. (MAN specification is defined by IEEE 802.6 protocol) [ps: I forgot the features: p]
WAN is also called remote network. It refers to a data communication network with wide coverage and relatively low transmission rate, with data communication as its main purpose. Features:
1. It is widely distributed.
2. Low data transmission rate.
3. The reliability of data transmission varies with different transmission media.
4. The topological structure is complex.
The topological structure of the network refers to the geometric shapes of communication lines and nodes in the network, which is used to express the structural appearance of the whole network and reflect the structural relationship between nodes. It affects the design, function, reliability and communication cost of the whole network, and is a very important element in the computer network.
What is a local area network?
A local area network (LAN) is a local geographical area (such as schools, factories and offices) connecting various computers. The computer communication network composed of external devices and databases is called LAN for short. It can be connected with remote LAN, database or processing center through data communication network or special data circuit to form a large-scale information processing system.
LAN has the following characteristics:
(1) coverage is generally within a few kilometers;
(2) use special transmission media to form a network, and the transmission rate is between 1 Mbit/s and 100 Mbit/s or higher;
(3) Multiple devices (usually between tens and hundreds) share a transmission medium;
(4) The layout of the network is relatively regular, and there are generally no switching nodes and routing problems in a single LAN;
(5) Topological structures are mainly bus type and ring type.
LAN is widely used in office automation, production automation and information processing systems.
There are three main types of LAN structures: Ethernet, token ring, token bus and fiber distributed data interface (FDDI) as the backbone of these three networks. They all follow the standards set by IEEE (American Institute of Electronic and Electrical Engineers) starting with 802. At present, the standards related to LAN are 1 1, namely:
Ieee 802.1-general network concepts and bridges, etc.
IEEE 802.2- logical link control, etc.
IEEE 802.3-CSMA/ Optical Disk Access Method and Physical Layer Specification
IEEE 802.4——ARCnet bus structure and access method, physical layer specification.
IEEE 802.5-token ring access method and physical layer specification, etc.
IEEE 802.6—— Access Mode and Physical Layer Specification of MAN
IEEE 802.7- Broadband LAN
IEEE 802.8—— Fiber LAN
IEEE 802.9—— ISDN local area network
IEEE 802. 10- network security
IEEE 802. 1 1- wireless local area network
Internet, also known as Internet, is the most influential international computer network in the world. Its accurate description is that the Internet is a network of networks. It uses TCP/IP network protocol to connect various physical networks of different types, scales and geographical locations into a whole. It is also an international communication network collection, which combines modern communication technology with modern computer technology and integrates various information resources in various departments and fields, thus forming an information resource network enjoyed by online users. Its appearance is the inevitable and symbol of the world from industrialization to informationization.
Internet originated from ARPAnet established by ARPA, the predecessor of DARPA, in 1969. The original ARPANET was mainly used for military research purposes. 1972, ARPANET first met the public and became the symbol of the birth of modern computer network. Another important contribution of ARPAnet in technology is the development and use of TCP/IP protocol family. ARPAnet has laid a foundation for the existence and development of Internet, and solved a series of theoretical and technical problems of interconnection between heterogeneous computer networks.
At the same time, the emergence and development of local area network and other wide area networks have played an important role in the further development of the Internet. Among them, the National Science Foundation (NSF) has the greatest influence, which established the National Science Foundation Network (NSFnet). It completely replaced ARPAnet as the backbone of the Internet in June 1990, but NSFnet's greatest contribution to the Internet is to open the Internet to the whole society. With the rapid growth of online traffic, in September, 1990, an advanced network and science company, ANS (Advanced Network &; Science Company). Its purpose is to build a T3 backbone network nationwide, which can transmit data at a rate of 45Mb/s, equivalent to transmitting 14 00 pages of text information per second. As of 199 1, all backbone networks of NSFnet have been connected with T3 backbone networks provided by ANS.
In recent ten years, with the development of society, science and technology, culture and economy, especially the development of computer network technology and communication technology, people pay more and more attention to the development and utilization of information resources, which effectively stimulates the development of the Internet. On the Internet, there are more than 65,438+000 businesses classified according to demand, including advertising companies, airlines, agricultural production companies, arts, navigation equipment, bookstores, chemical industry, communications, computers, consulting, entertainment, finance and trade, various shops and hotels, etc. It covers all aspects of social life and is the epitome of the information society.
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