AT&T DS1/DMi/ISDN-PRI manual System 85 and Generic 2 Synchronization Software Operation

SYNCHRONIZATION OF DIGITAL FACILITIES 5-9

a duplicated synchronization system, the same DS1 facility provides the primary and secondary reference for both duplicated halves. Figure 5-5, Duplicated Synchronization Architecture and Cross Coupling, shows a System 85 or Generic 2 with a duplicated architecture and cross-coupled cables.

PRIMARY

DS1

INTERFACE

SECONDARY

DS1

INTERFACE

SCS 0

SECONDARY

PRIMARY

SCS 1

MODULE

CLOCK OR TMS CLOCK 0

MODULE CLOCK OR TMS CLOCK 1

SWITCHING NETWORK 0

PORT

CARRIERS

SWITCHING NETWORK 1

Figure 5-5.Duplicated Synchronization Architecture and Cross Coupling

The TN767 is a DS1 circuit pack for a hybrid module; the ANN11 is a DS1 circuit pack for a traditional module. The standard cable that comes with the TN767 is the H600307. It can be ordered in eight different lengths, up to 650 feet, by ordering one of eight different group numbers (groups 1 - 8). See System 85 R2V4 to DEFINITY Communications System Generic 1.1 via ISDN PRI Access (555-037-233), DEFINITY Communications System Generic 1.1 to 4ESS via ISDN PRI Access (555-037-234), and DEFINITY Communications System Generic 2.1 to 4ESS via ISDN PRI Access (555-037-237), for specific cabling and administrative information.

System 85 and Generic 2 Synchronization Software Operation

The synchronization software consists of a series of tasks that monitor several system status parameters and thus maintain the best synchronization source online. (The online source is the synchronization reference currently in control. This reference can be either the primary or secondary reference, or an on-board local oscillator.) Several levels of control are maintained. One level is controlled by a 1-second software task that uses the system status to keep the best incoming DS1 reference clock online. The other is controlled both by hardware and the 1-second software task to maintain a healthy SCS on line. If a SCS can receive a suitable reference clock from a DS1, then the best combination is chosen.

The principal error conditions used to determine if a switch to a different DS1 clock reference is needed are, in order of importance: