The Internet Protocol Suite is the set of 网络传输协议 that implement the protocol stack on which the Internet and most commercial networks run. It is sometimes called the TCP/IP protocol suite, after the two most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were also the first two defined.

The 网络传输协议 like many can be viewed as a set of layers, each layer solves a set of problems involving the transmission of data, and provides a well-defined service to the higher layers based on using services from some lower layers. Higher layers are logically closer to the user and deal with more abstract data, relying on lower layers to translate data into forms that can eventually be physically manipulated.

The 网络传输协议 can be roughly fitted to the OSI模型 which describes a fixed set of 7 layers and some vendors like to use this model. However not all of these layers fit well with ip based networking (which really involves a varying number of layers depending on the design of the applications and the underlying network) and some believe that trying to fit the internet protocol suite to the OSI模型 does more to confuse than to help.

目录

• 1 分层
  • 1.1 应用层
  • 1.2 传输层
  • 1.3 网络层
• 2 Layers in the Internet Protocol stack
  • 2.1 The link layer
  • 2.2 The Internetwork layer
  • 2.3 The transport layer
  • 2.4 The application layer
• 3 Development
• 4 How IP Kills and Eats Competitive Networks
• 5 Implementations
• 6 See also
• 7 References
• 8 External links
• 9 TCP/IP 参考文献

分层

TCP/IP参考模型分为四层。应用层(Application Layer)，传输层(Transport Layer)，网络层(Internet Layer)，链路层(Link Layer)。

应用层

该层包括所有和应用程序协同工作，利用基础网络交换应用程序专用的数据的协议。如,

• HTTPS(Hypertext Transfer Protocol over Secure Socket Layer, or HTTP over SSL),安全超文本传输协议。
• HTTP(Hypertext Transfer Protocol),超文本传输协议。
• TELNET (Teletype over the Network, 网络电传) ，通过一个终端(terminal)登陆到网络(运行在TCP协议上)。
• FTP (File Transfer Protocol, 文件传输协议) ，由名知义(运行在TCP协议上) 。
• SMTP (Simple Mail Transfer Protocol，简单邮件传输协议) ，用来发送电子邮件(运行在TCP协议上) 。
• DNS (Domain Name Service，域名服务) ，用于完成地址查找，邮件转发等工作(运行在TCP和UDP协议上) 。
• NTP (Network Time Protocol，网络时间协议) ，用于网络同步(运行在UDP协议上) 。
• SNMP (Simple Network Management Protocol, 简单网络管理协议) ，用于网络信息的收集和网络管理。

传输层

该层提供端对端的通信。最重要的传输层协议是传输控制协议TCP。

• 传输控制协议TCP (Transport Control Protocol) - 数据流传输（面向连接，可靠）
• 用户数据报文协议UDP (User Datagram Protocol) - 数据报文传输(无连接不可靠)

网络层

该层负责数据转发和路由。从该层上面往下看，可以认为底下存在的是一个不可靠无连接的端对端的数据通路。最核心的协议当然是IP协议。此外还有ICMP，RIP,OSPF,IS-IS,BGP,ARP,RARP等。

Layers in the Internet Protocol stack

There is some discussion about how to map the TCP/IP参考模型 onto the OSI模型. Since the TCP/IP and OSI protocol suites do not match precisely, there is no one correct answer.

In addition, the OSI模型 is not really rich enough at the lower layers to capture the true layering; there needs to be an extra layer (the Internetworking layer) between the Transport and Network layers. Protocols specific to a particular network type, but which are run on top of the basic hardware framing, ought to be at the Network layer. Examples of such protocols are ARP and the Spanning Tree Protocol (used to keep redundant bridges idle until they are needed). However, they are local protocols and operate beneath the internetwork functionality. Admittedly, placing both groups (not to mention protocols which are logically part of the internetwork layer, but run on top of the internetwork protocol, such as ICMP) all at the same layer can be confusing, but the OSI model is not complex enough to do a better job.

The following diagram attempts to show where various TCP/IP and other protocols would reside in the original OSI模型l:

7 Application e.g. HTTP, SMTP, SNMP, FTP, Telnet, SIP, SSH, NFS, RTSP, XMPP, Whois, ENRP 6 Presentation e.g. XDR, ASN.1, SMB, AFP, NCP 5 Session e.g. ASAP, TLS, SSH, ISO 8327 / CCITT X.225, RPC, NetBIOS, ASP, Winsock, BSD sockets 4 Transport e.g. TCP, UDP, RTP, SCTP, SPX, ATP, IL 3 Network e.g. IP, ICMP, IGMP, IPX, BGP, OSPF, RIP, IGRP, EIGRP, ARP, RARP, X.25 2 Data Link e.g. Ethernet, Token ring, HDLC, Frame relay, ISDN, ATM, 802.11 WiFi, FDDI, PPP 1 Physical e.g. wire, radio, fiber optic, Carrier pigeon

Commonly, the top three layers of the OSI model (Application, Presentation and Session) are considered as a single Application Layer in the TCP/IP suite. Because the TCP/IP suite has a comparatively lightweight session layer, consisting of opening and closing connections under TCP and RTP and providing different port numbers for different applications under TCP and UDP, these functions may be augmented by individual applications (or libraries used by those applications). Similarly, IP is designed around the idea of treating the network below it as a black box so it can be considered as a single layer for the purposes of discussing TCP/IP.

4 Application
(OSI layers
5 through 7) e.g. HTTP, FTP, DNS
(routing protocols like BGP and RIP, which for a variety of reasons run over TCP and UDP respectively, may also be considered part of the Internetwork layer) 3 Transport
(OSI layers
4 and 5) e.g. TCP, UDP, RTP, SCTP
(routing protocols like OSPF, which run over IP, may also be considered part of the Internetwork layer) 2 Internetwork
(OSI
layer 3) For TCP/IP this is the Internet Protocol (IP)
(required protocols like ICMP and IGMP run over IP, but may still be considered part of the Internetwork layer; ARP does not run over IP) 1 Link
(OSI layers
1 and 2) e.g. Ethernet, Wi-Fi, MPLS, etc.

The link layer

The Link layer is not really part of the Internet protocol suite, but is the method used to pass packets from the Internet layer of one device to the Internet layer of another. This process can be controlled both in the software device driver for the network card, as well as on firmware or specialist chipsets. These will perform data link functions such as adding a packet header to prepare it for transmission, then actually transmit the frame over a physical medium. On the other end, the link layer will receive data frames, strip off the packet headers, and hand the received packets to the Internet layer.

However, the link layer is not always so simple. It may also be a Virtual private network (VPN) or tunnel, where packets from the Internet layer, instead of being sent over a physical interface, are sent using a tunneling protocol and another (or the same) protocol suite. The VPN or tunnel is usually established ahead of time, and has special characteristics that direct transmission out a physical interface does not (for example, it may encrypt the data going over it). This recursive use of the protocol suite can be confusing since the link "layer" is now an entire network. But it is an elegant method for implementing often complex functions. (though care is needed to prevent a packet that is wrapped and sent through a tunnel being repeatedly re-wrapped and sent down the tunnel again).

The Internetwork layer

As originally defined, the Network layer solves the problem of getting packets across a single network. Examples of such protocols are X.25, and the ARPANET's Host/IMP Protocol.

With the advent of the concept of internetworking, additional functionality was added to this layer, namely getting data from the source network to the destination network. This generally involves routing the packet across a network of networks, known as an internet.

In the internet protocol suite, IP performs the basic task of getting packets of data from source to destination. IP can carry data for a number of different h

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