In this chapter we present an overview of token ring networks, IEEE 802.5. Unlike Ethernet/802.3 LANs in which nodes contend for media access, token ring LANs use a token-passing scheme; that is, media access in token ring LANs is controlled by the possession of a token. We discussed general issues relating to token passing, including a comparison of random access and token passing protocols, in Chapter 5, which you might want to review before proceeding. In addition to token ring, the IEEE standards include a second token passing protocol called token bus. Although token bus use is uncommon, we present a brief comparison of the two token passing schemes for completeness. An outline of the major topics we present in this chapter follows:

• Definition and Operation (Questions 1 2)

• Frame Formats (Question 3)

• Priority Scheduling (Question 4)

• Monitor Stations (Questions 5 6)

• Physical Layer Issues (Questions 7 8)

• Token Ring vs. Token Bus (Question 9)

• Advantages and Disadvantages of Token Ring Networks (Question 10)

• Switched, Dedicated, and Full-Duplex Token Ring (Questions 11 14)

• High-Speed Token Ring (Question 15)

• Token Ring's Future (Question 16)