Computer Layer 7 Network

The advantages of layering:
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First, the physical layer (Physical Layer)

The lowest or first layer of the OSI model specifies Activate, maintain, close the mechanical characteristics, electrical characteristics, functional characteristics and process characteristics between the communication endpoints, providing a physical medium for transmitting data for the upper layer protocol.

At this layer, protocol data units are bits.

Typical specification representatives belonging to the definition of the physical layer include: RS-232, RS-449, RS-485, USB2.0, IEEE-1394, xDSL, X.21, V.35, RJ-45, etc.

The interconnected devices at the physical layer include: hubs, repeaters, and so on.

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 unreliable physical media. 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.

Representatives of data link layer protocols include: LLC, SDLC, HDLC, MAC, PPP, STP, Frame Relay, CSMA/CD, CSMA/CA, etc.

The interconnected devices at the data link layer include bridges, switches, and so on.

Logical Link Control LLC (Logical Link Control) protocol

Synchronous data link control SDLC (Synchronous Data Link Control)

protocol High-level data link control HDLC (High-Level Data Link Control) protocol

Multiple access control MAC (Multiple Access Control) protocol

Point- to-point protocol PPP (Point to Point Protocol)

spanning tree Protocol STP (Spanning Tree Protocol)

Carrier Sense Multiple Access with Collision Detection CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

Carrier Sense Multiple Access with Collision Avoidance CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)

3. Network Layer

The third layer of the OSI model, its main function is to translate the network address into the corresponding physical address 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.

Representatives of network layer protocols include: IP, ARP, IPX, DDP, RIP, OSPF, RARP, ICMP, IGMP, NetBEUI, etc.

The interconnected devices at the network layer include: routers, etc.

Internet Protocol IP (Internet Protocol)

Address Resolution Protocol ARP (Address Resolution Protocol)

Internetwork Packet Exchange Protocol IPX (Internetwork Packet Exchange Protocol)

Datagram Delivery Protocol DDP (Datagram Delivery Protocol)

Routing Information Protocol RIP (Routing Information Protocol)

Open Shortest Routing First Protocol OSPF (Open Shortest Path First)

Reverse Address Translation Protocol RARP (Reverse Address Resolution Protocol)

Internet Control Message Protocol ICMP (Internet Control Message Protocol)

Internet Group Management Protocol IGMP (Internet Group Management Protocol)

NetBEUI (NetBIOS Extended User Internet, NetBIOS User Extended Interface Protocol)

X. 25 (a packet-switched network protocol)

Ethernet (Ethernet protocol)

NWLink--Microsoft implementation of IPX/SPX transmission protocol

4. Transport Layer (Transport Layer)

The most important layer in the OSI model is the first end-to-end , that is, the host-to-host hierarchy. 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.

Transmission Control Protocol TCP (Transmission Control Protocol)

User Datagram Protocol UDP (User Datagram Protocol)

Sequenced Packet Exchange Protocol SPX (Sequenced Packet Exchange Protocol)

Name Binding Protocol NBP (Name Binding Protocol)

ATP (AppleTalk Transaction Protocol)--Apple Corporation

The

fifth layer of the OSI model, the fifth layer of the OSI model, manages the session process between 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 the two nodes by inserting checkpoints in the data, and decide whether the communication is interrupted and where to resend when the communication is interrupted. .

Sixth, the presentation layer (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.

Representatives of application layer protocols include: FTP, Telnet, SMTP, TFTP, HTTP, POP3, NNTP, IMAP4, HTTPS, SNMP, DNS, SMB, BOOTP, NFS, NCP, etc.

The interconnected devices at the application layer include: Gateway (Gateway).

File Transfer Protocol FTP (File Transfer Protocol), port number 21;

Remote Terminal Protocol Telnet (Remote Terminal Protocol), port number 23;

Simple Mail Transfer Protocol SMTP (Simple Mail Transfer Protocol), port number 25;

Simple File Transfer Protocol Protocol TFTP (Trivial File Transfer Protocol), port number 69;

Hypertext Transfer Protocol HTTP (Hypertext Transfer Protocol), port number 80;

Post Office Protocol POP3 (Post Office Protocol), port number 110;

Network News Transfer Protocol NNTP ( Network News Transport Protocol), the port number is 119;

Internet Mail Access Protocol IMAP4 (Internet Mail Access Protocol), the port number is 143;

HTTPS (Hypertext Transfer Protocol over Secure Socket Layer), the port number is 443 ;

Simple Network Management Protocol SNMP (Simple Network Management Protocol)

Domain Name Service Protocol DNS (Domain Name Service)

Server Message Block Protocol SMB (Server Message Block Protocol)

Bootstrap Protocol BOOTP (Bootstrap Protocol)

Network File System NFS (Network File System)

Network Core Protocol NCP (NetWare Core Protocol)

X. 500 (a directory service system protocol)

AFP (AppleTalk File Protocol) - Apple's network protocol suite for exchanging files