IBM Nways 8260, Manual

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Figure 84. Components of Dual Phase Lock Loop
The reduction in the jitter would allow you to have longer lobe distances and
higher number of station per ring segment. More details about the number of
supported stations and the lobe cable length are provided in 8.6, “Active Port
Technology” on page 142.
The DPLL is used in all the 8260 token-ring modules to ensure that the amount of
jitter which enters the backplane has been minimized. This is the case with the
passive modules as well as the active modules. However, active modules such
as the 18-port active per-port switching module, 18-port active module switching
module, and the dual-fiber repeater module implement one DPLL at every port,
while the passive modules such as the 20-port passive module, implements just
one DPLL at the interface to the backplane. The positioning of the two PLLs on
each port of the active module is shown in Figure 85 on page 140.
Chapter 8. 8260 Token-Ring Support
139