Networking Explained, 2nd Edition

Chapter 10: Fiber Distributed Data Interface (FDDI) 357

• On token ring networks, one clock on the network is responsible for providing

clocking signals for all nodes on the cable. The main clock node also provides an

“elastic” buffer capability that slides to compensate for speed differentials that

appear on the network; this is referred to as jitter. In a 100-Mbps FDDI environ-

ment, this type of clocking mechanism is impractical and difficult to maintain. At

4 Mbps, the bit-time is 250 ns as compared to 10 ns per bit-time at 100 Mbps. Con-

sequently, FDDI nodes provide their own clock (hence a “distributed” clocking

scheme) and correct for timing ...