-1995, IEEE, New York, 1995. REFERENCES 5. Information Technology-Part 5: Token Ring Access Method and Physical Layer Specification, ANSI/IEEE 802.5, 1995 ed., IEEE, New York, 1995. 6. Fiber Distributed Data Interface (FDDI)-Token Ring Physical Layer Medium Dependent, ANSI X3.166-1990, ANSI, New York, 1990. 7. Fiber Distributed Data Interface (FDDI) Physical Layer Protocol (PHY-2), ANSI X3.231-1994, ANSI, New York, 1994. 8. Fiber Distributed Data Interface (FDDI): Token Ring Media Access Control-2 MAC-3, ANSI X.239-1994, ANSI, New York, 1994. 9. Internetworking Troubleshooting Seminar Presentation, Hewlett-Packard Co., Tempe, AZ, Jan. 1995. 10. ChipCom promotional material, ChipCom, Southboro, MA, 1995. 11. High-Speed Networking-Options and Implications, ChipCom, Southboro, MA, 1995. 12. Cisco, www.cisco.com/univercd/cc/td/doc. ENTERPRISE NETWORKS II: WIDE AREA NETWORKS 12.1 WIDE AREA NETWORK DEPLOYMENT Wide area networks (WANs) provide data connectivity over much greater expanses than their local area network counterparts. Data rates on WANs are lower. One reason is that in many cases WANs are transported over the PSTN voice channels, either analog or digital. In either case there is a limited bit rate capacity. In this chapter we will cover two types of WANs. These are: 1. TCP/IP protocol family 2. Frame relay and some of its variants Two other WAN families of protocols that I am sure that many readers are familiar with have become obsolete. These are ITU-T(CCITT) Rec.X.25 and the Integrated Services Digital Networks (ISDN). Each of these, however, has left its mark for posterity. Here I mean that some element or part of these protocols has been lifted or purloined for use on new, more modern protocols. LAPB (link access protocol, B-channel) has been taken from X.25 covering OSI layer 2. Another example is LAPD (link access protocol, D-channel) taken from ISDN and has become the basic protocol structure (layer 2) for frame relay. 12.1.1 Introductory Comments Whereas the conventional LAN discussed in Chapter 11 