58 097-55501-01 Issue 6 – June 2003
1
TimeHub 5500 System Guide
two output driver slots (shelf front) for each letter group is for redundancy,
not to provide additional outputs. A single output driver card supplies 40
outputs, a pair of output driver cards in a letter grouping also supplies 40
outputs with the enhancement that those outputs are protected in the event
of a single output driver card failure.
1.9 Redundancy Considerations
The interconnections between the master and expansion shelf are designed
to support redundancy in several areas. Each of these areas is independent
of the others. In other words, if one type of redundancy is lost the other
areas of redundancy are not compromised.
1.9.1 Clock Redundancy
Clock timing, framing, and communication are provided to the expansion
shelves by both master shelf clock cards (CLK1 and CLK2). If either clock
card is removed, the expansion shelf continues to receive the necessary
signaling from the other clock card. This behavior is essentially the same as
the way clock cards provide redundant timing to output cards on a master
shelf, except that for expansion shelves the redundant clock signaling is
conveyed between shelves via the link cables.
1.9.2 Link Cable Redundancy
Each link cable conveys identical information from the master shelf to the
expansion shelf. Master shelf CLK1 and CLK2 signaling is present on both
link cables so that as long as one of the link cables is attached and working
properly, the expansion shelf is able to receive timing from any clocks that
are present in the master shelf.
1.9.3 Expansion Controller Card Redundancy
Each EC card receives complete signaling information from both link cables.
This means that, when both links are present, each EC card is receiving two
sets of identical signaling. If either EC card is removed, the remaining EC
card provides all of the necessary signaling between the output cards in the
expansion shelf and the clocks in the master shelf.
1.9.4 Output Card Redundancy
Each output card in an expansion slot-pair (i.e. "A", "B", …, "H") receives
clocking information from whichever clocks are installed in the master shelf.
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