OVERVIEW

We saw in Chapter 2 that more sophisticated services demanded by user applications are built from basic services in a layered architecture. We also discussed the ODN architecture for communication networks. In this chapter we study the seven-layer Open Systems Interconnection (OSI) model for the logical layering of functions in data networks. The OSI model can be regarded as more detailed specifications of the ODN model, although they were developed long before the ODN model.

We then discuss the important implementations of the OSI model, beginning with the major local and metropolitan area network implementations of the data link layer, from Ethernet and token ring to FDDI and DQDB (Distributed Queue Dual Bus), Frame Relay, and Switched Multimegabit Data Service (SMDS). Other important implementations of the data link layer are presented in Chapters 5 and 6. We explain the Internet and the TCP/IP networks in Chapter 4.

By the end of this chapter, you will be able to estimate the limitations of each implementation in terms of speed, delay, and versatility and to judge which implementation best meets an organization's needs. You will also understand the advances that are likely to occur in the near future and what they offer.

Section 3.1 describes the OSI model. Section 3.2 is devoted to Ethernet and section 3.3 to the token ring network; sections 3.4 through 3.7 describe the FDDI, DQDB, Frame Relay, and SMDS networks, respectively. The reader may skip particular sections without loss in continuity.

3.1 OSI AND IP...