Nortel Meridian 1 Option 11C, Administration And Maintenance

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Option 11C ISDN BRI Administration and Maintenance
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Chapter 4 — Network clocking
Introduction
This chapter describes digital network clocking as it applies to systems
equipped with the ISDN BRI feature.
Note: The Option 11 is a member of the Meridian 1 family of systems.
References to Meridian 1 or Meridian 1 SL-1 in this chapter include the
Option 11 system unless stated otherwise.
The Need for Synchronization
When digital signals are being transported over a communication link, the
receiving end must operate at the same frequency as the originating end to
prevent loss of information. This is referred to as link synchronization.
If both ends of a communication link are not in synchronization, data bit slips
will occur and therefore a loss of data will result. In general, accurate timing
is very important, but more importantly, synchronized timing is a must for
reliable data transfer.
When only two Meridian 1 PBX systems are interconnected in an isolated
private digital network, synchronization can be achieved by operating the two
systems in a master/slave mode whereby one system derives its timing from
the other. In a network of digital systems, however, slips can be better
prevented by forcing all digital systems to use a common reference clock
through a network clocking hierarchy (see Figure 12).