Lucent Technologies DDM-2000 OC-3 User Manual

363-206-285
Transmission and Synchronization Interfaces
Issue 3 June 2001
5-45
Synchronization Reconfiguration in an Access Ring 5
Figure 5-23a shows the access ring operating in its normal configuration. The
DDM-2000 OC-3 Multiplexer at the CO is externally timed, and each of the other
DDM-2000 OC-3 Multiplexers are line-timed in a counterclockwise direction. The
SQU message is sent to indicate where timing is traceable to an external BITS
and where it is valid to be used. The TLB message is sent on the interface that is
being used as the line timing reference and, thus, where using that timing would
create a timing loop. Synchronization messaging and automatic synchronization
have both been enabled for this network.
In Figure 5-23b, a fiber has been cut between sites A and B. Immediately, the
DDM-2000 OC-3 Multiplexer at site B enters holdover and sends out the internal
clock (IC) message to site C. The DDM-2000 OC-3 Multiplexer at site B cannot
switch to line time from site C because it is receiving the TLB message on that
interface.
Figure 5-23. Synchronization Reconfiguration — Access Ring (Sheet 1 of 3)
PRS
Traceable
BITS
DDM-2000
DDM-2000
DDM-2000
PRS
Traceable
BITS
Sync Flow
a) Before Failure
SQU
Site A
Site D
Site B
Site C
SQU
SQU
SQU
TLB
TLB
TLB
SQU
DDM-2000
DDM-2000
SQU
Site A
Site D
Site B
Site C
SQU
SQU
TLB
TLB
SQU
b) Failure Occurs,
Site B Changes Message
DDM-2000
DDM-2000
DDM-2000
STRATUM 3 if using a TG3 at site B, or IC if using a TGS.
IC
*
*

Lucent Technologies DDM-2000 OC-3 Specifications

General

Brand	Lucent Technologies
Model	DDM-2000 OC-3
Category	Multiplexer
Language	English