A, OSI seven-layer reference model
Open Systems Interconnection Reference Model Communication (English: Open System Interconnection Reference Model, abbreviated as OSI), referred to as the OSI model (OSI model), a concept model proposed by the International Organization for Standardization, trying to make a variety of computer in the world It is a standard framework within the interconnect network. It is defined in ISO / IEC 7498-1.
Two, OSI seven-layer model overview
The physical layer (Physical Layer): The main criteria defining the physical device, such as a cable interface types, the interface of the optical fiber type, transmission rates for the various transmission media, and the like. Its main function is to convert the data into a bit stream , corresponding to the cable, optical fibers and the like.
Data Link Layer (Data Link Layer): responsible for network addressing, error detection and error correction, this layer usually provide error detection and correction, to ensure reliable data transmission. When the header and tail to be added to the data packet, it will form a frame. Data list head (DLH) a method comprising physical address and the error detection and error correction. Data end of the list (the DLT) is a string of data packet indicating the end of the string, its main role is encapsulated into the bit stream data frame , corresponding to hubs, repeaters, switches and the like.
Network layer (Network Layer): provide routing communications addressed to the host of different LANs, the role of the data packets encapsulated into frames , corresponding to routers, three exchange.
Transport Layer (Transport Layer): definition of transmission protocol TCP / UDP. TCP (Transmission Control Protocol, a reliable, connection-oriented, full duplex streaming low transmission efficiency for high transmission reliability, the data amount of data). UDP (User Datagram Protocol, TCP characteristics and on the contrary, for the less demanding transmission reliability, a small data amount of data, such as QQ chat data is transmitted in this way), mainly from the lower layer data received segmentation and transmission destination address after restructuring, is often called a data segment this layer .
The session layer ( the Session Layer ): responsible for setting up and maintaining a communication connection between two computers in the computer network data transmission , a transport layer (port number: transmit and receive ports) to establish a data transmission path, mainly in your initiating a session between the system or accept the session request (need to recognize each other device may be a MAC or IP host name).
The presentation layer ( the Presentation Layer ): to convert data format compatible with the recipient's system and a format suitable for transmission . Information system ensures that a transmitted application layer may be read by the application layer of another system. For example, PC program to communicate with another computer, wherein a computer using an extended binary coded decimal interchange code (the EBCDIC), and another using American Standard Code for Information Exchange (ASCII) to represent the same character. If necessary, the presentation layer to achieve conversion between data formats through the use of a plurality of through-format.
The application layer (Application Layer): to provide for the application software is provided an interface, communication between the application software to set the other OSI layers is closest to the user, which is the user's application layer (e.g. e-mail, file transfer and terminal emulation).
Three, OSI seven-layer model layers corresponding agreement
| 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 (presentation layer having function) |
| Session Layer | ADSP·ASP·H.245·ISO-SP·iSNS·NetBIOS·PAP·RPC· RTCP · SMPP · SCP · SSH · ZIP · SDP (session layer having function) |
| 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 · · Ethernet Token Ring Lou FDDI · Frame Relay · GPRS · EVDO · HSPA · HDLC · PPP · L2TP · ISDN · STP |
| Physical Layer | The ethernet cards · · power line communication modem (PLC) · SONET / SDH (Synchronous Digital Network) · G.709 (optical transport network) optical fibers · · · coaxial twisted-pair Ethernet protocol |