计算机网络协议，记录
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Concept map
Layer descriptions and protocols
1. Physical Layer
The lowest or first layer of the OSI model specifies the mechanical, electrical, functional, and process characteristics between activating, maintaining, and shutting down communication endpoints, and provides a physical medium for upper-layer protocols to transmit data.
At this layer, protocol data units are bits.
The interconnected devices at the physical layer include: hubs, repeaters, and so on.
Physical layer: (typical equipment: repeater, hub, network cable, HUB) Data unit: bit (Bit)
Ethernet Physical Layer, Modem, PLC, SONET/SDH, G.709, Optical Fiber, Coaxial Cable, Twisted Pair
Second, the data link layer (Datalink Layer)
The second layer of the OSI model, it controls the communication between the network layer and the physical layer, and its main function is to provide reliable transmission on an unreliable physical medium. The role of this layer includes: physical address addressing, data framing, flow control, data error detection, retransmission and so on.
At this layer, the protocol data unit is a frame.
The interconnected devices at the data link layer include bridges, switches, and so on.
Data link layer: (typical equipment: network card, bridge, switch) Data unit: frame (Frame)
PPP (Point-to-Ponit Protocol) point-to-point protocol is byte-oriented and consists of three parts: a method for encapsulating IP datagrams into serial links; a link control for establishing, configuring and testing data link connections protocol
Stop waiting protocol:
CSMA/CD (Carrrier Sense Multiple Access with Collision Detection) carrier sense multiple access/collision detection protocol. In a bus-type network, the essence of the protocol is carrier sense and collision detection. Before the carrier sense sends data, it firstly detects whether there are other computers sending data on the bus, such as temporarily not sending data to avoid collision. Collision detection is that the computer detects the signal voltage on the channel while sending data.
ARQ (Automatic Repeat-reQuest) automatic repeat request protocol, one of the error correction protocols, including stop-waiting ARQ protocol and continuous ARQ protocol, error detection, positive confirmation, timeout retransmission and negative confirmation followed by retransmission and other mechanisms.
3. Network Layer
The third layer of the OSI model, its main function is to translate the network address into the corresponding physical ground, and decide how to route the data from the sender to the receiver. The role of this layer includes: routing data packets between subnets, realizing congestion control, Internet interconnection and other functions.
At this layer, the protocol data unit is a packet.
The interconnected devices at the network layer include: routers, etc.
Network layer: (typical equipment: routers, firewalls, multi-layer switches) Data unit: data packets (Packet)
IP (IPv4 · IPv6) (Internet Protocol) Protocol for interconnection between networks
ARP (Address Resolution Protocol) is the address resolution protocol, which realizes the physical address of the IP address.
RARP (Reverse Address Resolution 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 (Internet Group Management Protocol) Internet Group Management Protocol is a multicast protocol in the Internet protocol family, which is used by IP hosts to report their group membership to any directly adjacent router.
Fourth, the transport layer (Transport Layer)
The most important layer in the OSI model is the first end-to-end, host-to-host level. Its main function is to segment the upper layer data and provide end-to-end, reliable or unreliable transmission. In addition, the transport layer also handles end-to-end error control and flow control issues.
At this layer, the protocol data units are segments.
Representatives of transport layer protocols include: TCP, UDP, SPX, etc.
Transport Layer: (Typical Devices: Processes and Ports) Data Units: Segments
The TCP (Transmission Control Protocol) transmission control protocol provides reliable connection-oriented services. Before transmitting data, a connection must be established and released after the end. Reliable full duplex channel. Reliable, orderly, no loss, no repetition.
UDP (User Datagram Protocol) user datagram protocol does not need to establish a connection before sending data, does not use congestion control, does not guarantee reliable delivery, and best effort delivery.
5. Session Layer
The fifth layer of the OSI model manages the session process between the hosts, that is, it is responsible for establishing, managing, and terminating the session between the processes. Its main function is to establish a communication link, keep the communication link unblocked in the session process, synchronize the dialogue between two nodes by inserting checkpoints in the data, and decide whether the communication is interrupted and where to resend when the communication is interrupted. .
6. Presentation Layer
The sixth layer of the OSI model, the translator between the application and the network, is responsible for transforming the upper layer data or information to ensure that the application layer information of one host can be understood by the application of another host. The data conversion of the presentation layer includes data decryption and encryption, compression, format conversion, etc.
7. Application Layer
The seventh layer of the OSI model is responsible for providing an interface for the operating system or network application to access network services. The term "application layer" does not refer to a particular application running on the network. The services provided by the application layer include file transfer, file management, and e-mail information processing.
The interconnected devices at the application layer include: Gateway (Gateway).
File Transfer Protocol FTP (File Transfer Protocol), port number 21;
Hypertext Transfer Protocol HTTP (HypertextTransfer Protocol), port number 80;
Simple Network Management Protocol SNMP (Simple Network Management Protocol)
Domain Name Service Protocol DNS (Domain Name Service)
network File system NFS (Network File System)
Application Layer: (Typical Devices: Applications such as FTP, SMTP, HTTP)
DHCP (Dynamic Host Configuration Protocol) dynamic host allocation protocol, using UDP protocol to work, has two main purposes: to automatically assign IP addresses to internal networks or network service providers, to users or internal network administrators as a central management for all computers s method. Enables plug-and-play networking.
FTP (File Transfer Protocol) file transfer protocol <port number 21> reduces or eliminates the incompatibility of processing files under different operating systems.
HTTP (Hypertext Transfer Protocol) hypertext transfer protocol <port number 80>, transaction-oriented application layer protocol
SMTP (Simple Mail Transfer Protocol) Simple Mail Transfer Protocol <port number 25> is used to send mail.
RPC (Remote Procedure Call Protocol) (RFC-1831) Remote Procedure Call Protocol
Concept map
Reprinted to the blog post:
Protocols at various layers
of computer networks Common layered protocols in computer networks