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Protocols and Protocol Layers
Many of the addressing, error-checking, retransmission, and acknowledgment services most commonly associated with networking take place at the Network and Transport OSI layers. (Refer to Chapter 2.) Protocol suites are often referred to by the suite’s Transport and Network protocols. In TCP/IP, for instance, TCP is a Transport layer protocol and IP is a Network layer protocol. (Note, however, that TCP/IP predates OSI and diverges from OSI in a number of ways.)


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IPX/SPX is another protocol suite known by its Transport and Network layer protocols, but the order of the protocols is backward from the way the protocols are listed in TCP/IP. IPX is the Network layer protocol; SPX is the Transport layer protocol.

The lower Data Link and Physical layers provide a hardware specific foundation, addressing items such as the network adapter driver, the media access method, and the transmission medium. Transport and Network layer protocols such as TCP/IP and IPX/SPX rest on that Physical and Data Link layer foundation, and, with the help of the NDIS and ODI standards, multiple protocol stacks can operate simultaneously through a single network adapter. (Refer to the discussion of NDIS and ODI in Chapter 2.)

Upper-level protocols provide compatibility with a particular networking environment. For instance, the so-called NetBIOS over TCP/IP stack provides Microsoft clients with TCP/IP.

This chapter describes the common protocol suites and many of the important protocols associated with them. In addition to TCP/IP and IPX/SPX, some of the common Transport and Network layer protocols are the following: