Overview of Network Protocols
Communication between computers must also follow protocols at different levels to realize computer communication.
1. Physical layer
Definition: defines the physical device standards, such as the interface type of the network cable, the interface type of the optical fiber, the transmission rate of various transmission media, etc. Its main function is to transmit bit streams (that is, 1 and 0 are converted into current strength for transmission, and after reaching the destination, they are converted into 1 and 0, which is what we often call digital-to-analog conversion and analog-to-digital conversion). A layer of data is called bits.
Second, the link layer (link layer): local address (postman)
Ethernet (Ethernet) and WiFi are the most common link layer protocols today.
Definition: How to format data for transmission, and how to control access to physical media, this layer typically also provides error detection and correction to ensure reliable transmission of data.
At the link layer, information is transmitted in units of frames. In the frame, there are the receiving address (Source, SRC) and the sending address (Destination, DST), as well as a check sequence (Frame Check Sequence) that can detect errors. Of course, the most important thing in the frame is the data to be transmitted (payload) . The most important thing in a frame is the data to be transmitted (payload). These data often conform to higher-layer protocols for use by the upper layers of the network.
Third, the network layer (network layer) zip code (post office) such as: IP protocol (IPv4 · IPv6) Internet Protocol (the protocol for interconnection between networks)
Definition: Provides connection and routing between two host systems in a network located in different geographical locations. The development of the Internet has greatly increased the number of users accessing information from sites around the world, and the network layer is the layer that manages this connection. .
What about having one computer on WiFi communicate with another computer on Ethernet? We need a "man in the middle": the router. A router has multiple network cards (NIC, Network Interface Controller), and each NIC can access multiple networks and understand the corresponding connection layer protocol. When a frame is routed to another network, the router reads the frame's information and rewrites it to send to the other network. So the router is like a post office with branches in both communities. Therefore, the post office requires that the address written on the letter paper must be a "zip code" that conforms to the official regulations, that is, an IP address. Each post office generally connects multiple communities, and a community can also have multiple post offices leading to different communities. Sometimes a letter has to go through multiple post offices to finally reach its destination, a process called routing . The post office connected the separate local area networks into the internet, which eventually constituted the global internet.
Fourth, the transport layer (transport layer) recipient (administrator) such as: TCP protocol (Transmission Control Protocol) transmission control protocol, UDP protocol (User Datagram Protocol) user datagram protocol
The above three-layer protocol allows communication between different computers. But there are actually many processes in the computer, and each process may have communication needs. Transport layer protocols, such as TCP and UDP, use port numbers to identify recipients (a process). When writing a letter, we write the destination port. When the letter reaches the destination administrator, he will identify the port number according to the transport layer protocol and send the letter to different people.
Definition: defines some protocols and port numbers for transmitting data (WWW port 80, etc.), such as: TCP (Transmission Control Protocol, low transmission efficiency, strong reliability, used for transmitting data with high reliability requirements and a large amount of data), UDP (User Datagram Protocol, which is the exact opposite of TCP characteristics, is used to transmit data with low reliability requirements and a small amount of data, such as QQ chat data is transmitted in this way), mainly for data received from the lower layer. Segmentation and transmission, and then reorganization after reaching the destination address, this layer of data is often called a segment.
TCP and UDP protocols are two different transport layer protocols. The UDP protocol is similar to our letter exchange process. The TCP protocol is like frequent communication between two lovers. A little lover has so many feelings to express that he writes several letters in a row. The other party must put the letters in order to see the full meaning. The TCP protocol also has functions such as controlling network traffic.
Five, application layer (application layer) recipient address (industry terminology standard) such as: HTTP protocol (Hypertext Transfer Protocol) hypertext transfer protocol, SSH (Secure Shell) secure shell protocol
DNS (Domain Name Resolution), FTP (File Transfer Protocol) file transfer protocol, IMAP4 (Internet Message Access Protocol 4) is the fourth version of the Internet Information Access Protocol
Definition: The OSI layer closest to the user that provides network services for user applications such as email, file transfer, and terminal emulation.
Through the above several layers of protocols, we can already communicate between any two people (processes). However, everyone actually works in a different industry. Some are lawyers, some are diplomats. For example, in the communication between lawyers, strict lawyer terminology will be used to avoid disputes. Another example is the communication between diplomats, which must conform to a certain diplomatic format to avoid diplomatic misunderstandings. Another example is spies passing encrypted messages through ciphers. The application layer protocol is a further terminology specification for the content of the letter. The protocols of the application layer include HTTP protocol for Web browsing, FTP protocol for transferring files, IMAP for Email and so on.
Types of protocols at each layer
Physical Layer:
Ethernet Physical Layer, Modem, PLC, SONET/SDH, G.709, Optical Fiber, Coaxial Cable, Twisted Pair
Data Link Layer:
Wi-Fi, Ethernet, 802.11, 802.16, WiMAX, ATM, DTM, Token Ring, FDDI, Frame Relay, GPRS, EVDO, HSPA, HDL
Network layer:
IP (IPv4 · IPv6) Internet Protocol (protocol for interconnection between networks)
ARP: Address Resolution Protocol is the address resolution protocol, which realizes the realization of its physical address through the IP address.
RARP : Reverse Address Resolution Protocol The reverse address translation protocol allows physical machines on the LAN to request their IP addresses from the gateway server's ARP table or cache.
ICMP: (Internet Control Message Protocol) Internet Control Message Protocol. It is a sub-protocol of the TCP/IP protocol suite and is used to transmit control messages between IP hosts and routers.
ICMPv6:
IGMP: The Internet Group Management Protocol (IGMP) is a multicast protocol in the Internet protocol family for IP hosts to report their group membership to any directly adjacent router.
RIP : Routing Information Protocol (RIP) is a standard for exchanging routing information between gateways and hosts.
OSPF : (Open Shortest Path First Open Shortest Path First).
BGP : (Border Gateway Protocol) Border Gateway Protocol, a routing protocol used to connect independent systems on the Internet
IS-IS: (Intermediate System to Intermediate System Routing Protocol) Intermediate System-to-intermediate routing protocol.
IPsec: "Internet Protocol Security" is an open standards framework for ensuring private and secure communications over Internet Protocol (IP) networks by using encrypted security services.
Transport layer:
TCP (Transmission Control Protocol) Transmission Control Protocol
UDP (User Datagram Protocol) User Datagram Protocol
DCCP (Datagram Congestion Control Protocol) Datagram Congestion Control Protocol
SCTP (STREAM CONTROL TRANSMISSION PROTOCOL) Stream Control Transmission
Protocol RTP (Real-time Transport Protocol or RTP for short) real-time transport protocol
RSVP (Resource ReSer Vation Protocol) resource reservation protocol
PPTP (Point to Point Tunneling Protocol) point-to-point tunneling protocol
Application layer:
DHCP (Dynamic Host Assignment Protocol)
DNS (Domain Name Resolution)
FTP (File Transfer Protocol) File Transfer Protocol
Gopher (English original: The Internet Gopher Protocol Chinese definition: (RFC-1436) Internet Gopher Protocol)
· HTTP (Hypertext Transfer Protocol) Hypertext Transfer Protocol
· IMAP4 (Internet Message Access Protocol 4) is the fourth version of Internet Information Access Protocol
· IRC (Internet Relay Chat) Network Chat Protocol
· NNTP (Network News Transport Protocol) RFC-977 ) Network News Transfer Protocol
XMPP Extensible Message Processing Field Protocol
POP3 (Post Office Protocol 3) is the third version of Post Office Protocol
SIP Signaling Control Protocol
SMTP (Simple Mail Transfer Protocol) Simple Mail Transfer Protocol
SNMP (Simple Network Management Protocol)
· SSH (Secure Shell) Secure Shell Protocol
· TELNET Remote Login Protocol
· RPC (Remote Procedure Call Protocol) (RFC-1831) Remote Procedure Call Protocol
· RTCP (RTP Control Protocol) RTP Control Protocol
· RTSP (Real Time Streaming Protocol) Real-time Streaming Protocol
· TLS (Transport Layer Security Protocol) Secure Transport Layer Protocol
· SDP (Session Description Protocol) Session Description Protocol
· SOAP (Simple Object Access Protocol) Simple Object Access Protocol
GTP general data transmission platform
STUN (Simple Traversal of UDP over NATs, UDP simple traversal of NAT) is a network protocol
NTP (Network Time Protocol) Network Time Protocol