156 Clock Controller description and installationIntroduction This chapter introduces the NTRB53 Clock Controller, and providesprocedures on how to install this clock controller on Large Systems.The NTRB53 Clock Controller replaces the QPC471H and QPC775F innew systems. QPC471H and QPC775F Clock Controllers continue to besupported.Note: The NTRB53 Clock Controller cannot be combined with aQPC775 or a QPC471 card in one systemThe illustrations used in the description section depict a Small System.However, the system can also be representative of a Large System.Description This section provides an overview on the use of clock controllers. For LargeSystems, the following clock controllers are supported:• NTRB53• QPC471• QPC775Note: Clock controllers cannot be mixed in one system.The NTRB53 Clock Controller is available for all markets. The QPC471Clock Controller is available for U.S. markets. Vintages A through G of theQPC471 Clock Controller can be used in one system; vintage H of QPC471Clock Controllers cannot be mixed with clock controllers of other vintages.The QPC775E Clock Controller card is available for only Canadian andInternational markets.Need for synchronizationDigital trunking requires synchronized clocking so that a shift in one clocksource will result in an equivalent shift of the same size and direction in allparts of the network.When digital signals are being transported over a communication link,the receiving end must operate at the same frequency (data rate) asthe originating end to prevent loss of information. This is referred toas link synchronization. If both ends of a communication link are notin synchronization, data bit slips occur and therefore a loss of dataresults. In general, accurate timing is very important, but more importantlysynchronized timing is a must for reliable data transfer.Nortel Communication Server 1000ISDN Primary Rate Interface Installation and CommissioningNN43001-301 02.03 StandardRelease 5.5 7 December 2007Copyright © 2003-2007, Nortel Networks.
