Communications System Owner Manual
Table Of Contents
- Table of Contents
- ABOUT THIS DOCUMENT
- 1. INTRODUCTION TO CONNECTIVITY
- 2. COMMUNICATION SYSTEM NETWORKING (em AN OVERVIEW
- 3. TANDEM TIE TRUNK NETWORKS
- 4. MAIN-SATELLITE/TRIBUTARY (MS/T) NETWORKS THROUGH THE UDP OR MULTIPREMISES PACKAGES
- 5. ELECTRONIC TANDEM NETWORK (ETN) THROUGH THE ETN AND PNA PACKAGES
- 6. DISTRIBUTED COMMUNICATIONS SYSTEM (DCS)
- 7. DATA CONNECTIVITY - AN OVERVIEW
- 8. DATA COMMUNICATIONS CAPABILITIES
- 9. DATA COMMUNICATIONS CONFIGURATIONS
- A. RELATED DOCUMENTS
- B. SYNCHRONIZATION OF DIGITAL FACILITIES
- THE NEED FOR SYNCHRONIZATION
- SYNCHRONIZATION HIERARCHY
- CHANGES TO THE SCS SOFTWARE MADE AVAILABLE VIA SOFTWARE PATCHES
- NETWORK SYNCHRONIZATION AND ENGIINEERING
- AVAILABILITY OF SYNCHRONIZATION SOURCES
- CONCLUSIONS ON SYNCHRONIZATION
- USE OF GENERIC 2 AS A SYSTEM CLOCK REFERENCE
- USE OF GENERIC 1 AS A SYSTEM CLOCK REFERENCE
- C. TRUNKING TERMS AND CAPABILITIES
- D. COMMUNICATIONS PROTOCOLS
- E. LEAD DEFINITIONS
- F. NETWORKING FEATURES - AVAILABILITY MATRIX
- ABBREVIATIONS
- GLOSSARY
- INDEX

SYNCHRONIZATION OF DIGITAL FACILITIES B-21
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RULE 2:
A node may use a facility as a backup only if the node at the other end is not using that same facility as a
backup.
EXAMPLE FOR RULE 2
Figure B-13, Proper Use of Backup Facilities, illustrates an application of rule 2 and proper use of a
backup facility between nodes A and C.
B
C
D
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DIGITAL TRANSMISSION FACILITY
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PRIMARY FREQUENCY REFERENCE
SECONDARY (BACKUP) FREQUENCY REFERENCE
A
Figure B-13. Proper Use of Backup Facilities
Figure B-14, Improper Use of Backup Facilities, shows the same network arrangement but with improper
use of the backup facility between nodes A and C. This improper arrangement would form a timing loop if
node B should fail (nodes A and C would switch to their backup, which is each other).
RULE 3:
The transmission facilities associated with those nodes meeting Rules 1 and 2 and having the greatest
availability must be selected for primary and secondary synchronization facilities.