6.4 TCPIP | Internet-Enabled Business Intelligence


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	Internet-Enabled Business Intelligence By William A. Giovinazzo
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	Chapter 6. The Internet Network

6.4 TCP/IP

Let's revisit the purpose of a communications protocol. The intent is to provide a means by which two systems can communicate with one another. To establish this communication, they must both agree on a common language and syntax. The objective of the ISO/OSI reference model is to identify the pieces of the communication upon which agreement must be made. The protocol itself is the language and syntax that fits within that reference model. The protocol that has become the lingua franca of the Internet is TCP/IP.

TCP/IP was defined by the Networking Working Group in 1971 and integrated into the UNIX operating system shortly thereafter. The specifics of a TCP/IP implementation are defined in Request For Comments (RFCs). As the name implies, these documents invite users and concerned parties to make proposals and recommendations for new protocols and improvements to existing ones.

Figure 6.2 presents TCP/IP's alignment with the ISO/OSI reference model. The TCP/IP suite is composed of four layers, each of which corresponds to one or more layers of the ISO/OSI reference model. The process/application layer corresponds to the application, presentation, and session layers . Within this layer, we find the different applications that are part of the TCP/IP suite, such as the File Transfer Protocol (FTP), the Trivial File Transfer Protocol (TFTP), Telnet, and the Simple Mail Transfer Protocol (SMTP). FTP is described by RFC 959, TFTP by RFC 1350, Telnet by RFC 854, and SMTP by RFC 2821.

Figure 6.2. TCP/IP.

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The next layer in the suite is the Host-to-Host layer that corresponds to the Transport layer of the ISO/OSI reference model. The TCP of TCP/IP resides at this layer in the protocol suite. Recall that the Transport layer is responsible for reliable delivery of data across the network. This is the job of TCP. It creates the packets and ensures that they are acknowledged by the destination system. RFC 793 describes this protocol in detail. Another protocol residing at the Host-to-Host layer in the TCP/IP suite is the User Defined Protocol (UDP), as described in RFC 768. UDP differs from TCP in that it does not require an acknowledgment on the part of the destination system.

The Internet layer of the TCP/IP suite corresponds to the Network layer of the ISO/OSI reference model. Again, thinking back to the ISO/OSI discussion, we see that this layer's task is to move information across the network. The network layer examines the network layer address of a packet of information and passes it on to the next subnetwork via a router. It is at the Internet layer that we find the Internet Protocol (IP). IP fragments the packets into datagrams, routes them to the destination system, and reassembles inbound datagrams into packets.

The final layer of the TCP/IP suite is the Network Access layer. This layer corresponds to the Data Link and Physical layers of the ISO/OSI reference model. The Network Access layer establishes the physical connection between the networked systems. The IEEE standards we discussed in the previous section described the different network topologies that establish this connection. The IEEE 802.3 standard describes the Ethernet bus topology, while IEEE 802.4 describes a token bus and IEEE 802.5 describes a token ring.


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