1. DATA COMMUNICATION
Lecture-44

2. Recap of Lecture 43 Ethernet Implementations Other Ethernet Networks
Token Bus/Ring

3. Overview of Lecture 44
Token Ring
FDDI
Internet & internet

4. Token Ring Token Ring allows each station to send one frame per turn
Access method: Token passing

5. Token Ring

6. Access Control of Token Ring
Priority and reservation
Each station has a priority code
Time limits
Token Ring imposes a time limit to keep traffic moving

7. Monitor Stations
One station is designated as a monitor station to handle several problems
Monitor station generates a new token when it is lost
Monitor station removes recirculating data frames

8. Token Ring Frame

9. Data Frame Fields

10. Implementation Each station in the Token Ring regenerates the frame
One disabled or disconnected node could stop the traffic flow around the entire network
Each station is connected to an automatic switch

11. Implementation

12. Token Ring Switch

13. Multistation Access Unit (MAU)
Individual automatic switches are combined in to a hub
One MAU can support up to 8 stations
Although it looks like a star, it is in fact a ring

14. Multistation Access Unit (MAU)

15. FDDI
Fiber Distributed Data Interface standardized by ANSI and the ITU-T
100 Mbps LAN protocol
CDDI: Copper version of FDDI
Access method: Token passing

16. FDDI Time Registers Time registers
Values are set when the ring is initialized and do not vary
SA (Synchronous Allocation)
TTRT (Target Token Rotation Time)
AMT (Absolute Maximum Time)

17. FDDI Timers Timers Each station contains two timers
TRT (Token Rotation Timer) : Incrementing
THT (Token Holding Timer) : Decrementing

18. Station Procedure

19. Station Procedure THT is set to the difference between TTRT and TRT
THT = TTRT - TRT
TRT is reset to zero (TRT = 0)
The station sends S-frames during the time in SA
The station sends A-frames as long as THT  0
Release the token

20. Dual Ring

21. Dual Ring

22. Network
Access
Method
Signaling
Data Rate
Error
Control
Ethernet
CSMA/CD
Manchester
1, 10 Mbps No
Fast Ethernet
Several
100 Mbps
Gigabit Ethernet
1 Gbps
Token Ring
Token passing
Differential
4, 16 Mbps
Yes
FDDI
4B/5B, NRZ-I

23. Summary
Token Ring
FDDI

24. Suggested Reading Section 12.5, 12.6, 12.7
“Data Communications and Networking” 2nd Edition by Behrouz A. Forouzan