363-206-285
Transmission and Synchronization Interfaces
Issue 3 June 2001
5-39
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-3
Release 9.1 and later releases, synchronization messaging can also be done
using bits 5-8 of the S1 byte in the SONET overhead (not supported on OC-1
links). If a DDM-2000 OC-3 system is deriving timing from a given OC-N interface
and synchronization messaging is enabled on that interface (Kbyte messages and
Sbyte messages 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-3 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 list
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-3 Multiplexers cannot generate these messages, but they
could be retransmitted and supported for autoreconfiguration if any of these are
received by a DDM-2000 OC-3 Multiplexer.
‡ The TG3 circuit pack can generate a stratum 3 signal.
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