Basic knowledge of computer network

An ISO and OSI seven layer model

• What is ISO?
• Iso
• OSI seven layer model?
• The conceptual model, presented by the International Standards Organization, aims to provide a standard framework for the interconnection of a wide range of computers and networks worldwide. It divides the computer network architecture into 7 layers

1. At the bottom of the physical layer, ensure that the original data is transmitted on a variety of physical media, in bits.
2. The role of the data link layer is physical address addressing, data detection error, the bitstream is encapsulated into frames.
3. The network layer routes the packets between subnets, which are congestion control and Internet interconnection. Unit is packet packet
4. The transport layer provides data transfer services for end-to-end communication. This layer has TCP and UDP protocols, and data units are segments.
5. The session layer manages the session process between hosts, and uses the data to insert checkpoints to synchronize data, access authentication and session management functions. Unit is a message.
6. Represents the encryption and decryption of layer data, compressed decompression. Unit is a message.
7. The application layer provides an interface for operating system or network applications to access network services. Complete specific network applications by applying inter-process interactions.

Tcp / ip:

Network interface layer: PPP, FDDI

Internetwork: IP, ICMP

Transport layer: TCP, UDP

Application layer: FTP, TELNET

The difference between TCP and UDP:

TCP: Transmission Control Protocol. is a connection-oriented, reliable, byte-stream-based communication protocol for Transport layer

UDP: User Datagram Protocol. In the network it is the same as the TCP protocol for processing packets, is a non-connected protocol

TCP connection-oriented, UDP for non-connected

Reliable TCP transmission, UDP transmission unreliable

TCP is used to transmit large amounts of data, and UDP is used to transmit

Slow TCP transmission, fast UDP transmission

TCP supports point-to-point communication, and UDP supports one-to-many, many-to-one, many-to-many communications.

Three-time handshake:

1. Establish Connection Agreement (three handshake)

(1) The client sends a TCP message with a SYN flag to the server. This is the message 1 in the three-time handshake process.
(2) server-side response client, this is the 2nd message in the three-time handshake, this message with both an ACK flag and a SYN flag. So it represents the response to the client's SYN message, and it also flags the SYN to the client and asks the client if it is ready for data communication.
(3) The customer must again respond to the service segment an ACK message, which is the message segment 3.

Basic knowledge of computer network