AT&T Telephone DS1/DMi/ISDN-PRI Manual de usuario Pagina 95
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- Tabla de contenidos
- MARCADORES
Valorado. / 5. Basado en revisión del cliente
SYNCHRONIZATION OF DIGITAL FACILITIES
5-5
MASTER REFERENCE
FREQUENCY
NOTE
SLAVE
NODES
DIGITAL TRUNK
PRIMARY REFERENCE
NOTE: The dashed lines indicate which nodes supply reference frequencies
and those facilities used to transmit the reference.
Figure 5-2. Synchronization Hierarchy
Switching nodes in digital networks are divided into synchronization layers called strata. There are
four strata, 1 to 4, where stratum 1 has the highest accuracy and stratum 4 the lowest. Public digital
networks use stratum 1, 2, and 3 synchronization. Historically, private digital networks used
stratum-4 clocks all synchronized together. However, to provide higher quality synchronization
performance, stratum-3 clocks are currently being used with some customer-premises equipment.
Because of recent changes within the synchronization hierarchy, stratum-4 clocks are now defined as
stratum-4 type I or stratum-4 type II. The specifications for stratum-4 type I define limits that
minimize and control phase changes that occur while switching from one synchronization source to
another. However, stratum-4 type-II clocks do not comply with this specification and all other
stratum-4 specifications remain the same for both type-I and type-II clocks. Beginning in 1990,
public-network connections cannot use a stratum-4 type-II clock as a synchronization source (a
stratum-4 type-I clock can be used).
Each stratum from 1 to 4 is progressively less stable and less expensive clock. Within AT&T, there is
a system of stratum-1 clocks. These clocks use the AT&T standard reference frequency, formerly the
Bell System reference frequency. The stratum-1 output is transmitted to various public digital
network nodes via either broadband analog facilities or the DATAPHONE
®
Digital Service (DDS).
- AT&T 1
- DEFINITY 1
- CONTENTS 11
- CONTENTS xv 15
- ABOUT THIS DOCUMENT 19
- 1. INTRODUCTION 25
- INTRODUCTION 26
- DS1 TRANSMISSION AND CABLING 74
- 4. THE DIGITAL LOSS PLAN 83
- THE DIGITAL LOSS PLAN 84
- PRIMARY FREQUENCY REFERENCE 110
- DIGITAL TRANSMISSION FACILITY 111
- (Generic 2) 191
- ● Numbers between (0 and 255) 213
- Selection basis 219
- CIRCUIT PACK 247
- SYSTEM-PARAMETERS CUSTOMER 251
- OPTIONS 251
- DS1 CIRCUIT PACK screen 256
- TRUNK GROUP screen; 257
- GROUP MEMBER 257
- ASSIGNMENTS 257
- SYSTEM PARAMETERS 258
- CUSTOMER-OPTIONS 258
- PROCESSOR CHANNEL ASSIGNMENTS 260
- INTERFACE LINKS 260
- DATA MODULE screen 263
- NETWORK-FACILITES 267
- CBC TRUNK GROUP USAGE 275
- ALLOCATION 275
- TRUNK GROUP 280
- DIAL PLAN RECORD screen 281
- TRUNK GROUP screen 283
- DIAL PLAN RECORD 284
- NETWORK-FACILITIES screen 285
- 8. MAINTENANCE AND ALARMS 289
- MAINTENANCE AND ALARMS 290
- ≥ ES ≥ 2460 in 41 minutes 298
- ADMINISTRATION REQUIREMENTS 304
- ABBREVIATIONS 355
- GLOSSARY 359
- GLOSSARY GL-13 371
- GLOSSARY GL-17 375
- GLOSSARY GL-19 377
- INDEX IN-13 393
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