Computer Network 2

OSI Layer Seven Network model encyclopedia:

The OSI (open System Interconnection) seven-layer network model, known as the Open System Interconnect Reference Model, is a logical definition, a specification that divides the network logically into 7 layers. Each layer has relevant, corresponding physical devices, such as routers, switches.
OSI Seven layer model is a framework design method, the main purpose of building seven-layer model is to solve the compatibility problem of heterogeneous network interconnection, its main function is to help different types of host to achieve data transmission. Its greatest advantage is to distinguish between the three concepts of service, interface, and protocol, and to enable reliable communication between different networks with different systems through seven hierarchical structural models.

Diagram of it:

　　　　　　　　　　

Introduction of each layer:

"1" Physical layer: The main definition of physical equipment standards, such as the interface type of network cable, the interface type of optical fiber, the transmission rate of various transmission media. Its main role is to transmit the bitstream (that is, from 1, 0 to the current strength to carry out the transmission, after reaching the destination in the conversion to 1, 0, which is what we often call the digital-to-analog conversion and the ADC), the layer of data called bits.

"2" Data Link layer: Defines how to make data formatted for transmission and how to control access to physical media, a layer that often provides error detection and correction to ensure reliable data transmission.

"3" Network layer: to provide connectivity and path selection between two host systems located in geographically diverse networks, the development of the Internet has greatly increased the number of users accessing information from various sites around the world, and the network layer is the layer that manages this connection.

"4" Transport Layer: Defines a number of transmission data protocol and port number (WWW port 80, etc.), such as: TCP (Transmission Control Protocol, transmission efficiency is low, reliable, for transmission reliability requirements, high data volume data), UDP (User Datagram Protocol, and TCP characteristics, the opposite, For transmission reliability requirements are not high, data volume of small data, such as QQ chat data is transmitted through this way, the main is to be received from the lower layer of data segmentation and transmission, to the destination address and then re-reorganization, often this layer of data called a segment.

"5" Session layer: through the Transport Layer (port number: Transport port and receive port) to establish the data transmission path, mainly between your system to initiate a session or accept the session request (between the devices need to know each other can be IP can be Mac or hostname).

The "6" presentation layer: ensures that the information sent by the application layer of one system can be read by the application layer of the other system. For example, a PC program communicates with another computer, where one computer uses an extended 210 binary Interchange Code (EBCDIC) and the other uses the U.S. Information Interchange Standard Code (ASCII) to represent the same characters. If necessary, the presentation layer enables conversion between multiple data formats by using a pass-through format.

"7" Application layer: The OSI layer closest to the user, which provides network services for user applications such as e-mail, file transfer, and terminal emulation.

　　

The following list is the classification of some of the agreements, if the wrong or wrong place, I hope that the great God put forward a lot! In fact, the protocol between the three tiers of application, representation, and session can be shared (due to the fact that the network protocol has attributed them to a class)

Application Layer	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
Presentation Layer	Http/html FTP Telnet ASN.1 (with presentation layer capability)
Session Layer	ADSP ASP h.245 ISO-SP iSNS NetBIOS Pap RPC RTCP SMPP SCP SSH Zip SDP (with session layer capability)
Transport Layer	TCP UDP TLS DCCP SCTP RSVP PPTP
Network layer	IP (IPv4 IPV6) · ICMP ICMPv6 IGMP Is-is IPSec BGP RIP OSPF ARP RARP
Data Link Layer	Wi-Fi (IEEE 802.11) · WiMAX (IEEE 802.16) · ATM DTM Token Ring · Ethernet Road · FDDI Frame Relay · GPRS EVDO HSPA HDLC PPP L2TP ISDN Stp
Physical Layer	Ethernet Card • Modem • Power line communication (PLC) · SONET/SDH (Optical synchronous Digital transmission network) · G.709 (optical transmission network) · Optical fiber Coaxial cable Twisted pair Wire

Computer Network 2