The call stage characteristics define the way an ISDN call is initiated, acknowledged, and completed. The specifics of ISDN call stages and their supported characteristics are defined in the OSI reference model Network layer definition of ISDN.
Formal call stage components include the following, in order:
The formal call components as presented in the preceding list can also be tracked through a typical ISDN call negotiation as shown in Figure 1-16.
This chapter discussed how networks began and how they have been increasing in complexity ever since. You also learned about the physical layout of early networks as well as the issues surrounding the evolution of contemporary intranets and what the future holds for network engineers. This chapter also established the physical foundations and needs of past, current, and future networks.
You also explored the OSI reference model down to each individual layer and learned how a typical data packet flows up and down the OSI layers as well as the way it flows between geographically separated networks. At this point, you should understand the basic functions of the logical network through the discussion and demonstrations illustrated.
The chapter continued with coverage of the LAN and WAN intranet topologies. The section on LAN topologies included coverage of the three most widely deployed topologies: Ethernet, Token Ring, and FDDI, as well as the standards and basic characteristics of each. The section on WAN topologies included coverage of the three most widely deployed topologies: Frame Relay, PPP, ATM, and ISDN. Discussion of each topology included the standards applicable for each and some of the more important aspects of each.
In conclusion, the reader should now understand the evolution of networks, intranet evolution, current challenges, physical and logical network fundamentals, popular LAN and WAN topologies. Chapter 2, Network Routing Fundamentals, will build further upon the foundations of networking covered in this chapter.