What is a network protocol? What are the commonly used application layer protocols?

Network protocol refers to a set of rules that must be followed when exchanging information between peer entities communicating with each other in a computer network. Commonly used application layer protocols: DHCP, DNS, FTP, Gopher, HTTP, IMAP4, IRC, NNTP, XMPP, POP3, SIP, SMTP, etc.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

What is a network protocol?

Network protocol refers to a set of rules that must be followed when exchanging information between peer entities communicating with each other in a computer network. It is a set of rules for all devices on the network (network servers, computers and switches, routers , firewall, etc.), which stipulates the formats that information must use during communication and the meaning of these formats.

Peer entities usually refer to information units at the same level in the computer network architecture. The general system network protocol includes five parts: communication environment, transmission service, vocabulary, information encoding format, timing, rules and procedures.

Most networks adopt a layered architecture. Each layer is built on the layer below it and provides certain services to the layer above it. The details of how to implement this service are The upper layer is shielded. The rules for layer n on one device to communicate with layer n on another device are layer n protocols. There are many protocols in each layer of the network. The protocols of the receiver and the sender at the same layer must be consistent, otherwise one party will not be able to recognize the information sent by the other party. Network protocols enable various devices on a network to exchange information with each other. Common protocols include: TCP/IP protocol, IPX/SPX protocol, NetBEUI protocol, etc.

Network protocols are composed of three elements:

(1) Semantics. Semantics is the interpretation of the meaning of each part of the control information. It specifies what control information needs to be sent, as well as the completed actions and responses.

(2) Grammar. Syntax is the structure and format of user data and control information, as well as the order in which the data appears.

(3) Timing. Chronology is a detailed description of the order in which events occur. (Also known as "synchronization").

People vividly describe these three elements as: semantics represents what to do, syntax represents how to do it, and timing represents the order of doing it.

What are the commonly used application layer protocols?

DHCP, DNS, FTP, Gopher, HTTP, IMAP4, IRC, NNTP, XMPP, POP3, SIP, SMTP, SNMP, SSH, TELNET, RPC, RTCP, RTP, RTSP, SDP, SOAP , GTP, STUN, NTP, SSDP, BGP, etc.

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