Computer Network Accessories for Commercial Internet Project YH00

Network interconnection refers to connecting more than two communication networks with one or more network communication devices through a certain method to form a larger network system. The purpose of network interconnection is to realize that users in different networks can communicate with each other, share software and data, etc.
The types of network interconnection mainly include:
Lan and LAN
Local area network and wide area network
Local area network and wide area network and local area network
Wan and wan
Open system interconnect edit that mechanical properties of the physical lay of the OSI ( open system inter connection ) open system interconnect network interconnect: the shape of the interface, the size, the number of pins, and the arrangement. Electrical performance: voltage, current, impedance, waveform, speed and balance characteristics of interface specified signals. Engineering specification: meaning, characteristics and standards of interface pins. How it works: determines how the data bit stream is transmitted, such as simplex, half duplex, or full duplex. Physical layer protocols are: RS232, RS 422, RS 423, RS 485 of EIA; International telegraph and telephone advisory Committee ( CCITT ) x 25, x 21, etc.; The data unit of the physical layer is bit, and the typical device is a hub hub. The physical characteristics of the transmission medium are shielded by the link layer of the network interconnection link layer to ensure reliable data transmission. Content includes media access control, connection control, sequence control, flow control, error control, arbitration protocol, etc. Link layer protocols are: character oriented communication protocol ( PPP ) and bit oriented communication protocol ( HDLC ). Arbitration protocol: 802.3, 802.4, 802.5, i.e., csma / CD ( carriersensultipleadwithwitheventaction ), token bus, token ring link layer data unit is a frame, to achieve access to MAC address, the typical device is switch. The network lay of that network interconnect layer manage the connection and routing. Connection: virtual circuits and datagram services. A virtual circuit is a connection - oriented data communication route established through a session. Datagrams are not connected - oriented, and each datagram has routing capabilities. The network layer's data units are packets, using IP addresses, and the typical device is router. This layer allows for flow control, but more flow control uses a second layer or a fourth layer. The network interconnect transport layer provides end-to-end service. Flow control and load balan can be realized. Transport layer information contains ports, control words, and checksums. The transport layer protocols are mainly TCP and UDP. The transport layer is located at the fourth layer of OSI, which uses the host itself. The main content of that session lay of the internet session layer is to authenticate, manage and determine the mode of communication through session. Once a connection is established, the task of the session layer is to manage the session. The presentation lay of that internet presentation layer mainly explain the meaning of communication data, such as code conversion, format conversion and so on, so that different terminals can express. It also includes encryption and decryption, compression and decompression, etc. The application layer of network interconnection application layer should be a direct user-oriented program or service, including system program and user program, such as www, FTP, DNS, pop 3 and SMTP are application layer services. Data is a process of packaging data from the application layer to the physical layer when sending, and a process of unpacking data from the physical layer to the application layer when receiving, which can be divided into three groups from the functional point of view, layer 1 and layer 2 solve the network channel problem, layer 3 and layer 4 solve the transmission problem, and layer 5, layer 6 and layer 7 deal with the access to the application process. From the control point of view can be divided into two groups, layer 1, 2, 3 is the communication subnet layer, layer 4, 5, 6, 7 is the host control layer.