FDDI

1. FDDI Seminar on resume writing for CS Students Presenter: Yuri A. Tijerino Ph.D. Date: September 29th, 2003 and October 29th, 2003 (same info for both seminars) Time: 3pm to 5pm Place: Room 151 in the Tanner Building

2. Objectives • Introduce CRC lab • Understand FDDI • Understand Token Bus

3. Ethernet vs. Token Ring:Ethernet Dominance • Open standard • Proprietary platforms “forced” to support standards or lose value FDDI Market $220M 1997, $40M 2001. Fast Ethernet $150/port FDDI $750/port

4. Ethernet vs. Token Ring:Media Access Control Methods • Contention (Ethernet) • performs better than token passing on low utilization LANs • high utilization - collisions and retransmission when 2 stations try to communicate simultaneously • Token passing • high utilization - superior performance, no collisions • QoS – multimedia preference to some applications • used to control bus in USB, Firewire, and other emerging shared media technologies

5. Comparison • FDDI uses 4b/5b NRZI (Non-Return to Zero Invert on ones) with 125 Mb/s baud rate to achieve 100 Mb/s data rate • 10BaseT Ethernet uses Manchester encoding with 20 Mb/s baud rate to achieve 10 Mb/s data rate. 2Volts or 0 volts for logic values. 802.3 • Base = Baseband - Baseband signaling simply means that Ethernet signals are the only signals carried over the media system. • 100BaseT Ethernet uses 4B/5B with 125 Mbps to achieve 100Mbps data rate. 802.3 • MLT3 (Multi-Level Transmission) • defines 3 levels of voltages +1 volt, 0 volt, -1 volt • Binary 1 is transmitted by changing to the adjacent voltage • Binary 0 is transmitted by maintaining the same voltage

6. Gig Ether • Copper • Uses 4 pairs of wires • 125MHz clock speed • PAM-5 uses five different voltage levels and defines each as a specific 2 bit pattern. 00, 01, 10, 11. Sends 2 bits each clock cycle • Fiber • 8b10B encoding to transmit data – enhanced version of the 4B5B used in fast Ethernet which allows data to be sent in 10-bit groups (2 overhead bits in each group)

7. 10Gig Ether • LAN version – parallel transmission through four separate fibers using 8b10B coding scheme with clock speed of 3.125GHz. • WAN Version -- Uses 64B66B encoding – sends 64 bits of data with 2 bits of overhead (over SONET)

8. Ethernet vs. Token Ring:Response Time vs. Load

9. Overview • Token Ring Networks • PRONET: 10Mbps and 80 Mbps rings • IBM: 4Mbps token ring • 16Mbps IEEE 802.5/token ring • 100Mbps Fiber Distributed Data Interface (FDDI)

10. Basic Idea • frames flow in one direction: upstream to downstream • special bit pattern (token) rotates around ring • must capture token before transmitting • release token after done transmitting • immediate release • delayed release • remove your frame when it comes back around • stations get round-robin service

11. Physical Properties of FDDI Dual Ring Configuration Single and Dual Attachment Stations Downstream Neighbor Upstream Neighbor SAS Concentrator SAS SAS SAS SAS

12. Characteristics • Each station imposes a delay (e.g., 50ns) • Maximum of 500 stations • Upper limit of 100km (200km of fiber) • Uses 4B/5B encoding • Can be implemented over copper (CDDI)

13. Timed Token Algorithm • Token Holding Time (THT): upper limit on how long a station can hold the token. • Token Rotation Time (TRT): how long it takes the token to traverse the ring. TRT <= ActiveNodes x THT + RingLatency • Target Token Rotation Time (TTRT): agreed-upon upper bound on TRT.

14. Algorithm • each node measures TRT between successive arrivals of the token • if measured TRT > TTRT, then token is late so don't send data • if measured TRT < TTRT, then token is early so OK to send data • define two classes of traffic • synchronous data: can always send • asynchronous data: can send only if token is early • worse case: 2xTTRT between seeing token • not possible to have back-to-back rotations that take 2xTTRT time

15. Token Maintenance • Lost Token • no token when initializing ring • bit error corrupts token pattern • node holding token crashes • Generating a Token (and agreeing on TTRT) • execute when join ring or suspect a failure • each node sends a special claim frame that includes the node's bid for the TTRT • when receive claim frame, update bid and forward • if your claim frame makes it all the way around the ring: • your bid was the lowest • everyone knows TTRT • you insert new token

16. Monitoring for a Valid Token • should see valid transmission (frame or token) periodically • maximum gap = ring latency + max frame <= 2.5ms • set timer at 2.5ms and send claim frame if it fires

17. Acknowledgements with Token Ring • Acknowledgement of a frame arrival can be done by destination by changing a bit at the tail of a frame

18. Token Bus • Uses broadcast channel, but the stations form a logical ring (13576824) • There is a special packet called the “token” • a station that has the token is allowed to transmit for a time • when the time is up it passes the token to next station in the ring • a station may only transmit what it has when the token arrived. If it has no frames to send then it simply passes the token on

19. Properties of the Token Bus • Useful in the real-time application when a guaranteed level of service is required • In heavy loads there is a very good utilization since token passing is only a small percentage of the traffic and there are no collisions • In very light loads there are delays caused by the token passing • If a station goes down there is a potential of a token being lost. A lost token can be detected and can be regenerated by the remaining active stations

20. Properties of the Token Bus • The token bus allows priorities. For example, high priority can be given to voice packets • The token bus can allow for quick turnaround on acknowledgements. The station that has the token allows the recipient to ack before sending the next frame • IEEE 802.4 is a standard for token buses running on broadcast channel