363-206-295
Transmission and Synchronization Interfaces
Issue 1
December 1997
5-21
Synchronization Provisioning Integrity
5
A welcome side feature of synchronization messaging is that it helps prevent
provisioning errors. Provisioned timing loops on the DDM-2000 Multiplexers will be
quickly detected through the synchronization messaging algorithm and prevented
by forcing a shelf into holdover. The system can then be reprovisioned correctly.
Feature Details and Options
5
As mentioned previously, SONET synchronization messaging is used to
communicate the quality of the subnetwork timing throughout the subnetwork. This
is done using bits 1-3 of the K2 byte found in the SONET overhead. In OC-12
Release 5.1 and later releases, synchronization messaging can also be done using
bits 5-8 of the S1 byte in the SONET overhead. If a DDM-2000 OC-12 system is
deriving timing from a given OC-N interface, and synchronization messaging is
enabled on that interface (Kbyte messages and Sbyte messages in OC-12 Release
5.1 and later are provisioned using the
set-ocn
command), the system interprets
the received message to determine its internal timing status. The system also
determines the state of the DS1 output, if the DS1 output is enabled. The
DDM-2000 OC-12 system also transmits over the particular OC-N interface and all
other OC-N interfaces that are enabled for synchronization messaging, the
appropriate message indicating the quality of its timing and its active timing mode.
Table 5-3 and Table 5-4 list the associated internal timing status and DS1 Output
states that are associated with synchronization messages received from the OC-N
interface when synchronization messaging is enabled. The tables lists the
messages from low to high quality.
Table 5-3.
Synchronization Messages using K2 Byte
Received Message
Active Timing Mode
∗
Default
DS1 Output State
Quality
Level
Don't Use
Holdover
AIS
7
Timing Looped Back (TLB)
Holdover
AIS
7
Stratum 4 †
Holdover
AIS
6
Internal Clock (IC)
OK to use
AIS
5
Internal Clock (IC) (w/TG3)
Holdover
AIS
5
Stratum 3 †‡
OK to use
Good
4
Stratum 2 †
OK to use
Good
3
Sync Quality Unknown (SQU)
OK to use
Good
2
Stratum 1 †
OK to use
Good
1
*
This column applies only when provisioned for line timing mode.
†
Presently, DDM-2000 OC-12 Multiplexers cannot generate these messages, but they
could be retransmitted and supported for autoreconfiguration if any of these are
received by DDM-2000 OC-12 Multiplexer.
‡
The TG3 circuit pack can generate a stratum 3 message.
