1. Computer network structure
Large-scale modern computer network: network edge, access network and network core
1. Network edge : All end systems connected to the network (for example: computers, servers, smartphones, etc. connected to the network) constitute the network edge.
2. Access network : the network that realizes the connection and access between the edge of the network and the core of the network
For large-scale and complex network end systems that are far apart, the network connection and communication between these end systems require data relay and forwarding by the network core. Generally, the core of the network is an ISP network operated by an operator, etc., which cannot directly extend to the user area. For example, at home, the user needs to use the access network to connect to the ISP.
Common network access technologies : telephone dial-up access (using modems), asymmetric digital subscriber line ADSL (common, using frequency division multiplexing technology), hybrid fiber coaxial cable HFC access network (cable modem, Using frequency division multiplexing technology, exclusive access), local area network (Ethernet, WIFi), mobile access network (personal device access to the network. For example: 2G/3G/4G)
3. Network core : a network composed of packet switching equipment interconnected by communication links, whose role is to realize data relay and forwarding between hosts on the edge of the network
Typical packet switching equipment: switches, routers
2. Data Exchange Technology
1. The purpose of computer network : to realize mutual data transmission and information exchange between hosts on the edge of the network
2. Data exchange network : The intermediate network does not need to care about the content of the transmitted data, but only provides data relay and exchange functions for the data from one node to another until it reaches the destination .
Switching node: the nodes that make up the switching network
Communication subnet: a collection of switching nodes and transmission media, that is, the core of the network.
3. Data exchange is the technical basis for realizing data transmission on the core of a large-scale network.
Common data exchange technology:
① Circuit switching : The telephone network is the earliest and largest circuit switching network. (For example: telephone dialing process)
Circuit switching includes three stages: establishing a circuit, transmitting data, and removing the circuit. ,
Disadvantages: waste of channel capacity and effective time
②Message exchange : The sender adds the information to be sent to the address of the sending/receiving host and other control information to form a complete message, and then store-forward between each node of the switching network in the unit of message To the destination host.
Disadvantages: Can not meet real-time communication speed requirements, node storage space is not enough, output link is occupied and cannot forward messages in time, causing messages to be discarded.
③ Packet switching : At present, a widely used technology. Packet switching divides the message into smaller data blocks . The data block plus address, serial number and other control information form data packets. Each packet is transmitted to the destination independently, and the destination divides the packet. Reassemble and restore to a message.
Advantages: The storage capacity of the switching equipment is low, the switching speed is fast, the reliable transmission efficiency is high, and it is more fair.
