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2. The Networker's Guide to TCP/IP


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2. The Networker's Guide to TCP/IP



The Origins of TCP/IP






Layer 3: IP Protocol



Layer 4: TCP and UDP






The Application Layer Protocols of the TCP/IP Suite






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Understanding the Network

From: Understanding the Network
Author: Michael Martin
Publisher: New Riders
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2. The Networker's Guide to TCP/IP

TCP/IP is the predominant network protocol in use today. Although proprietary networking protocols, like AppleTalk and IPX, still enjoy widespread use on local area networks (LANs), the increased demand for desktop-level access to the Internet, which utilizes the TCP/IP protocol suite for host to host communication has lead many networking environments to implement TCP/IP and abandon their proprietary protocol implementations altogether or implement TCP/IP alongside their proprietary LAN protocols. TCP/IP is well suited for both local and wide area networking applications, and is easily scalable to support networks of any size. It is not only capable of coexisting with other Layer 3 protocols, IP can be used to transport proprietary LAN protocol datagrams over IP WANs. TCP/IP was developed as the second generation network protocol for ARPAnet (Advanced Research Projects Administration Network), which was an experimental network funded by the U.S. government to research packet switching networks. The ARPA network and the technologies developed for it formed the foundation of the modem Internet. Development on TCP/IP began in 1973; it became available as a production protocol suite in 1983. Figure 2.1 illustrates TCP/IP's developmental timeline.


In the previous chapter, we examined the Internet-RM, OSI, and IEEE reference models. By becoming familiar with the different reference models, you gain a sense of the logical flow of the data communication process. Protocol theory, however, is often simpler than its physical deployment. Knowledge of the communication models is important, but it can be confusing. To minimize this confusion, the OSI-RM will be the default reference model in discussing the protocols and their respective layer of operation.

Figure 2.1. The TCP/IP development timeline.

The goal of this chapter is to describe the various protocols of the TCP/IP protocol suite. Using the OSI-RM model, the key elements of TCP/IP are covered: what each protocol does, its sequence in the suite, and services it needs to perform. This chapter also explores how the various protocols of the TCP/IP suite work together and how TCP/IP relates to other transport mechanisms (such as Ethernet and FDDI) that carry TCP/IP packets. An understanding of the material is crucial to anyone who is building or managing a TCP/IP based computer network.

The Origins of TCP/IP

TCP/IP gets its name from the most widely used protocols in the suite: Transmission Control Protocol (TCP), the OSI-RM Level 4 protocol that provides connection-oriented data transport service, and Internet Protocol (IP), the OSI-RM Level 3 protocol that provides datagram delivery and addressing facilities. Early in TCP/IP's development, its capability to provide network connectivity between different types of hosts was extolled as one of its greatest virtues.

This virtue has made TCP/IP the protocol on which most client/server computing is based. Most interactive application layer protocols use the client/server model to exchange data. Client/server is a transaction-based processing model. The client represents the user or device making a data request. This request is made using a common data exchange process or user interface to a server.

The server processes client requests by providing data that can be processed by the requesting client. Both the server and the client agree on the data exchange process before transactions are made. This is ensured because both the client and server are following a common application programming interface (API) that specifies how the transaction function calls will take place.

The capability of TCP/IP to function equally well across both WAN and LAN connections, coupled with its diverse computer platform support, makes TCP/IP the natural choice for connectivity in heterogeneous internetworking environments. Although TCP/IP is vendor-independent and in the public domain, it has required continuous development as computer and networking technologies have progressed. This development is overseen by the Internet Engineering Task Force (IETF), which consists of more than 80 sub-committees that develop, review and revise the technologies standards used on the Internet. The IETF operates under the Internet Society, a nonprofit organization that coordinates the development of the Internet.


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