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<UL>
<UL>
<UL>
<LI>
<A HREF="#E68E14" >A Quick Overview of TCP/IP Components</A></LI>
<UL>
<LI>
<A HREF="#E69E31" >Telnet</A></LI>
<LI>
<A HREF="#E69E32" >File Transfer Protocol</A></LI>
<LI>
<A HREF="#E69E33" >Simple Mail Transfer Protocol</A></LI>
<LI>
<A HREF="#E69E34" >Kerberos</A></LI>
<LI>
<A HREF="#E69E35" >Domain Name System</A></LI>
<LI>
<A HREF="#E69E36" >Simple Network Management Protocol</A></LI>
<LI>
<A HREF="#E69E37" >Network File System</A></LI>
<LI>
<A HREF="#E69E38" >Remote Procedure Call</A></LI>
<LI>
<A HREF="#E69E39" >Trivial File Transfer Protocol</A></LI>
<LI>
<A HREF="#E69E40" >Transmission Control Protocol</A></LI>
<LI>
<A HREF="#E69E41" >User Datagram Protocol</A></LI>
<LI>
<A HREF="#E69E42" >Internet Protocol</A></LI>
<LI>
<A HREF="#E69E43" >Internet Control Message Protocol</A></LI></UL>
<LI>
<A HREF="#E68E15" >TCP/IP History</A></LI>
<LI>
<A HREF="#E68E16" >Berkeley UNIX Implementations and TCP/IP</A></LI>
<LI>
<A HREF="#E68E17" >OSI and TCP/IP</A></LI>
<LI>
<A HREF="#E68E18" >TCP/IP and Ethernet</A></LI>
<LI>
<A HREF="#E68E19" >The Internet</A></LI>
<UL>
<LI>
<A HREF="#E69E44" >The Structure of the Internet</A></LI>
<LI>
<A HREF="#E69E45" >The Internet Layers</A></LI>
<LI>
<A HREF="#E69E46" >Internetwork Problems</A></LI></UL>
<LI>
<A HREF="#E68E20" >Internet Addresses</A></LI>
<UL>
<LI>
<A HREF="#E69E47" >Subnetwork Addressing</A></LI>
<UL>
<LI>
<A HREF="#E70E4" >The Physical Address</A></LI>
<LI>
<A HREF="#E70E5" >The Data Link Address</A></LI>
<LI>
<A HREF="#E70E6" >Ethernet Frames</A></LI></UL></UL>
<LI>
<A HREF="#E68E21" >IP Addresses</A></LI>
<LI>
<A HREF="#E68E22" >Address Resolution Protocol</A></LI>
<UL>
<LI>
<A HREF="#E69E48" >Mapping Types</A></LI>
<LI>
<A HREF="#E69E49" >The Hardware Type Field</A></LI>
<LI>
<A HREF="#E69E50" >The Protocol Type Field</A></LI></UL>
<LI>
<A HREF="#E68E23" >ARP and IP Addresses</A></LI>
<LI>
<A HREF="#E68E24" >The Domain Name System</A></LI>
<LI>
<A HREF="#E68E25" >Summary</A></LI>
<LI>
<A HREF="#E68E26" >Q&A</A></LI>
<LI>
<A HREF="#E68E27" >Quiz</A></LI></UL></UL></UL>
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<A ID="E66E2" NAME="E66E2"></A>
<H1 ALIGN=CENTER>
<CENTER>
<FONT SIZE=6 COLOR="#FF0000"><B>— 2 —</B>
<BR><B>TCP/IP and the Internet</B></FONT></CENTER></H1>
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<P>Before proceeding into a considerable amount of detail about TCP/IP, the Internet, and the Internet Protocol (IP), it is worthwhile to try to complete a quick outline of TCP/IP. Then, as the details of each protocol are discussed individually, they can be placed in the broader outline more easily, thereby leading to a more complete understanding in the next two chapters.
<BR>
<P>Just what is TCP/IP? As you saw on Day 1, it is a software-based communications protocol used in networking. Although the name TCP/IP implies that the entire scope of the product is a combination of two protocols—Transmission Control Protocol and Internet Protocol—the term TCP/IP refers not to a single entity combining two protocols, but a larger set of software programs that provides network services such as remote logins, remote file transfers, and electronic mail. TCP/IP provides a method for transferring information from one machine to another. A communications protocol should handle errors in transmission, manage the routing and delivery of data, and control the actual transmission by the use of predetermined status signals. TCP/IP accomplishes all of this.
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<NOTE>
<IMG SRC="note.gif" tppabs="http://www.mcp.com/817948800/0-672/0-672-30885-1/note.gif" WIDTH = 75 HEIGHT = 46>TCP/IP is not a single product. It is a catch-all name for a family of protocols that use a similar behavior. Using the term TCP/IP usually refers to one or more protocols within the family, not just TCP and IP.</NOTE>
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<P>In the first chapter, you saw that the OSI Reference Model is composed of seven layers. TCP/IP was designed with layers as well, although they do not correspond one-to-one with the OSI-RM layers. You can overlay the TCP/IP programs on this model to give you a rough idea of where all the TCP/IP layers reside. I do that in a little more detail later in this chapter. Before that, I take a quick look at the TCP/IP protocols and how they relate to each other, and show a rough mapping to the OSI layers.
<BR>
<P>Figure 2.1 shows the basic elements of the TCP/IP family of protocols. You can see that TCP/IP is not involved in the bottom two layers of the OSI model (data link and physical) but begins in the network layer, where the Internet Protocol (IP) resides. In the transport layer, the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are involved. Above this, the utilities and protocols that make up the rest of the TCP/IP suite are built using the TCP or UDP and IP layers for their communications system.
<BR>
<P><B><A HREF="02tyt01.gif" tppabs="http://www.mcp.com/817948800/0-672/0-672-30885-1/02tyt01.gif">Figure 2.1. TCP/IP suite and OSI layers.</A></B>
<BR>
<P>Figure 2.1 shows that some of the upper-layer protocols depend on TCP (such as Telnet and FTP), whereas some depend on UDP (such as TFTP and RPC). Most upper-layer TCP/IP protocols use only one of the two transport protocols (TCP or UDP), although a few, including DNS (Domain Name System) can use both.
<BR>
<P>A note of caution about TCP/IP: Despite the fact that TCP/IP is an open protocol, many companies have modified it for their own networking system. There can be incompatibilities because of these modifications, which, even though they might adhere to the official standards, might have other aspects that cause problems. Luckily, these types of changes are not rampant, but you should be careful when choosing a TCP/IP product to ensure its compatibility with existing software and hardware.
<P>TCP/IP is dependent on the concept of clients and servers. This has nothing to do with a file server being accessed by a diskless workstation or PC. The term <I>client/server</I> has a simple meaning in TCP/IP: any device that initiates communications is the client, and the device that answers is the server. The server is responding to (serving) the client's requests.
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