OSI seven layer model and TCP/IP protocol comparison

OSI (open System Interconnection), open Systems Interconnect Reference Model. From bottom to top seven-tier model features and their representative protocols:

• Physical Layer (physical) : Specifies the mechanical, electrical, functional, and process characteristics that activate, maintain, and close communication endpoints. This layer provides a physical medium for the upper level protocol to transmit data. bit, bit. Typical protocol representatives: eia/tia-232, eia/tia-499, v.35, v.24, RJ45, Ethernet, IEEE 802.3x (Ethernet) Physical layer, FDDI (Fiber distributed Data Interface, Fiber Distributed Data Interface) Physical layer

• Data Link Layer : Provides reliable transmission on unreliable physical media. The functions of this layer include: Physical address addressing, data framing, flow control, data error checking, re-sending, etc. frame, frames. Typical protocol representatives: SDLC (synchronous DataLink control, synchronous Data Link controls), HDLC (High-level Data link control, high-level link controls), PPP (point-to-point Dot-to-point), IEEE 802.3x Data Link layer, FDDI Data link layer, ATM (asynchronous Transfer mode, asynchronous Transfer Mode), IEEE 802.5 (Token Ring), frame Relay (Frame relay)

• Network Layer : Responsible for routing data packets between subnets. In addition, the network layer can also realize congestion control, Internet interconnection and other functions. Packet, pack. Typical protocol representative: IP, ICMP, IGMP, IPX, BGP, OSPF, RIP, IGRP, EIGRP, ARP, RARP, x.

• Transport Layer (Transport) : The transport layer is the first end-to-end, that is, the host-to-host hierarchy. The transport layer is responsible for segmenting the upper data and providing an end-to-end, reliable, or unreliable transmission. In addition, the transport layer also handles end-to-end error control and flow control issues. Segment, Duan. Typical protocol representative: TCP, UDP, TLS, RTP, SCTP, SPX, ATP, IL

• Session Layer : Manages the session process between hosts, which is responsible for establishing, managing, and terminating sessions between processes. The session layer also uses the insertion of checkpoints in the data to synchronize data. Typical protocol representatives: RPC, SQL, NFS, NetBIOS, SCP, ASP, SSH, Winsock, BSD sockets

• presentation Layer (Presentation) : Transforms the upper data or information to ensure that one host application layer information can be understood by another host's application. The data transformation of the presentation layer includes data encryption, compression, format conversion, and so on. Typical protocol representatives: TIFF, GIF, JPEG, PICT, ASCII, EBCDIC, encryption, MPEG, MIDI, HTML

• Application Layer (application) : An interface that provides access to network services for an operating system or network application. Typical protocol representatives: FTP, WWW, Telnet, NFS, SMTP, Gateway, SNMP, HTTP, Whois, SSH

Layers of the OSI layer seven model devices:

• Physical layer: A variety of transmission media (light, network cable), various types of DTE and DCE communication between the physical device (computer, HUB), all kinds of slots, sockets

• Data Link Layer: Two sub-tiers: LLC (Logical link Control, logical link-controlling layer), MAC (Media access control, press-level). Network cards, bridges, and Layer two switches

• Network layer: Routers, gateways, and layer three switches

• Transport layer: four-layer switch

• Session Layer: Layer five switch

• Presentation layer: Six-layer switch

• Application layer: computer, load balancer and 70% switch

TCP/IP network protocol
TCP/IP (transmission Control protocol/internet Protocol, Transmission Protocol/Network Protocol) is the most widely used protocol in the world, and its popularity is closely related to the rapid development of Internet. TCP/IP was originally designed for the prototype ARPANET of the Internet to provide a set of convenient and practical protocols that can be applied to a wide variety of networks, and it turns out that TCP/IP does this by making it easier to interconnect networks and adding more and more networks into the Internet Standard of fact.
The TCP/IP Reference model consists of four levels:

• Host-to-network layer: In fact, the TCP/IP reference model does not really describe the implementation of this layer, it only requires the ability to provide a provider to its upper-network interconnect layer, in order to pass IP packets on it. Because this level is not defined, its specific implementation will vary depending on the type of network.

• Network interconnect layer: Defines the grouping format and protocol, the IP protocol (Internet Protocol). In addition to the ability to complete routing, the network interconnect layer can also accomplish the tasks of interconnecting different types of networks (heterogeneous networks). In addition, the network interconnect layer also needs to complete the congestion control function.

• Transport layer: Enables a session to be made by the peer entity on the source and destination hosts. Two protocols with different quality of service are defined at the transport layer. That is, TCP (Transmission Control Protocol) and Subscriber Datagram Protocol UDP (User Datagram Protocol). The TCP protocol is a connection-oriented, reliable protocol. It sends a stream of bytes from one host to other hosts on the Internet without error. At the sending end, it is responsible for dividing the stream of bytes sent down into message segments and passing it to the lower layer. At the receiving end, it is responsible for reorganizing the received message to the upper layer. 　　 　　The TCP protocol also handles end-to-end traffic control to avoid slow-receiving receivers not having enough buffers to receive large amounts of data sent by the sender. UDP protocol is an unreliable, non-connected protocol, which is mainly applicable to the situations where the message is not ordered and the flow control is not required.

• Application layer: Includes the session layer and presentation layer in the OSI Reference model. Different application layer protocols are introduced for different network applications. Among them, there are TCP protocol based, such as FTP (file Transfer Protocol, Files Transfer Protocol), Telnet (Virtual Terminal protocol), HTTP (Hyper text Transfer Protocol, Hypertext link Protocol), UDP protocol based : such as SNMP, TFTP,NTP.

OSI seven-layer protocol and TCP/IP four-layer protocol comparison:

• Hierarchical structure
  Both the OSI reference model and the TCP/IP protocol are hierarchical and are based on the concept of a separate protocol stack. The OSI Reference Model has 7 layers, and the TCP/IP protocol has only 4 layers, that is, the TCP/IP protocol does not have a presentation layer and a session layer, and merges the data link layer and the physical layer into the network interface layer. However, there is a certain correspondence between the two layers.

• Features of the standard
  The standard of the OSI Reference model was first developed by ISO and CCITT (the predecessor of the ITU), with a strong communications background, and therefore also featured in a deep communication system, such as the quality of Service (QoS), error rate assurance, and only connection-oriented services. And it is to define a set of fully functional architecture, and then according to the framework to develop the corresponding protocols and systems.

  The TCP/IP protocol arises from the research and practice of Internet network, which is produced by the actual demand, and then standardized by the IAB, IETF and so on, rather than defining a rigorous framework before. and TCP/IP was first implemented in UNIX system, considering the characteristics of computer network, it is more suitable for the realization and use of computers.

• Connection Service
  The OSI network layer corresponds to the Internet layer of TCP/IP, the functions of the two are basically similar, but the addressing method has a great difference.

  The OSI address space is not fixed variable length, determined by the selected address naming method, up to 160byte, can accommodate a very large network, thus has a large growth space. According to the OSI protocol, each system on the network can have up to 256 communication addresses.

  The address space of the TCP/IP network is fixed 4byte (this is the case in the currently used IPV4, which expands to 16byte in IPv6). Each system on the network has at least one unique address corresponding to it.

• Transfer Service
  Both the OSI and the TCP/IP transport layer adopt different transmission strategies for different services. The OSI defines five different levels of services: TP1,TP2,TP3,TP4,TP5. The tcp/i p defines TCP and UDP two protocols, each with a connection-oriented and non-connection oriented nature. TCP and OSI in the TP4,UDP and OSI in the TP0 in the framework and function are basically the same, but there are some differences in the internal details.

• Application scope
  Because of the complexity of the system, and the design before the implementation, there are many design is too ideal, the computer software is not easy to implement, so the full implementation of the OSI Reference model of the system is not many, the scope of application is limited. The TCP/IP protocol, which is implemented in computer system, has a stable implementation in UNIX and Windows platform, and provides a simple and convenient programming interface (API), which can be used to develop rich applications. The TCP/IP protocol has become the de facto international and industrial standard for Internet interconnection.

OSI seven layer model and TCP/IP protocol comparison