| more topics
|
System-wide Programming Options - Clock Synchronization
Clock synchronization is an arrangement in which digital facilities operate from a common clock. Whenever digital signals are transmitted over a communications link, the receiving end must be synchronized with the transmitting end to receive the digital signals without errors.
The system synchronizes itself by extracting the timing signal from the incoming digital stream. If the system has one 100D module, 100R INA, or 100DCD, that module provides its own primary synchronization. If the system has at least one 800 NI-BRI module; more than one 100D, 100R INA, or 100DCD module; or a combination of 100D, 100R INA, or 100DCD modules and 800 NI-BRI modules, one of the connections provides primary clock synchronization for all 800 NI-BRI and 100D, 100R INA, or 100DCD module ports and for the system's time-division multiplexing (TDM) bus. The primary clock synchronization source must be identified during system programming. The factory setting either is the first 100D, 100R INA, or 100DCD module or the first port on the first 800 NI-BRI module in the carrier. This can be changed through system programming.
In the event of a maintenance failure of primary synchronization, backup synchronization can be provided by secondary and tertiary clock synchronization.
In addition, the source of synchronization is factory-set to Loop Clock Reference Source so that the clock is synchronized to the outside source. With a 100D, 100R INA, or 100DCD module, it can be set to Local Clock Reference Source so that the clock is free-running. This is not recommended, however, for most permanent installations or for systems with PRI. This setting must be made for the primary, secondary, and tertiary synchronization sources.
With digital tandem trunks, a single clock source should be used for all systems in the network. Generally, the rules for assigning clock sources are the same as for single systems. When the source for clock synchronization is not on a module in the local system, it is assigned as loop. A loop clock source may be a port connected to the PSTN or, in a network, may be the same type of port on a non-local system. When the source for clock synchronization is a local system module, it is assigned as local. There can be no more than one local clock source for digital tandem facilities in a network, and all other tandem facilities are assigned as loop. There does not have to be any local clock source in a network; all can be loop.
Networked systems do not always have an in-service digital PSTN facility available or active. For this reason, clock synchronization in some private networks requires choosing among other clock sources. In a network with three or more systems, it is best if all clock sources for the network are on either a hub system (star configuration) or a system that connects two other switches (series configuration). If the primary clock source is not functioning, then a secondary or tertiary source on such a system can serve either all other systems in the network or two other systems in a network. If a MERLIN LEGEND (Release 6.1 or later), DEFINITY ECS, DEFINITY BCS, or DEFINITY ProLogix Solutions system is included in the network and has functional digital PSTN facilities, it should provide the clock synchronization source. Details and examples are provided in the Network Reference.
The following lists the options for primary, secondary, and tertiary clock synchronization sources in order of preference:
|
Ports that are not in service should never be programmed as clock sources. |
