As mentioned previously, synchronization status messaging is used to communicate the quality of the subnetwork timing throughout the subnetwork.
In SONET/SDH networks, synchronization status messages use bits 5-8 of the S1 byte in the SONET/SDH overhead.
In Synchronous Ethernet networks, synchronization status messages use OAM Protocol Data Units (OAMPDUs) which are identified by specific header fields in the Ethernet frame. OAMPDUs are standard Ethernet MAC frames but are then identified through both the Length/Type as Slow Protocol frames (value 8809) and then specifically by a Subtype (value 0x0A) as OAMPDUs.
If an Alcatel-Lucent 1850 TSS-5 shelf/circuit pack is deriving timing from a given SONET/SDH or Ethernet interface, and synchronization status messaging is enabled on that interface, the system interprets the received message to determine the timing status. Alcatel-Lucent 1850 TSS-5 shelf/circuit packs also transmits over the particular SONET/SDH or Ethernet interface, and all other SONET/SDH or Ethernet interfaces that are enabled for synchronization status messaging, the appropriate message indicating the quality of its timing and its usability.
Table 6-9, SONET/SDH synchronization status messages lists the associated internal timing status and DS1/E1 output states that are associated with synchronization status messages received from the OC-n/STM-n interface when synchronization status messaging is enabled.
|
SONET |
SDH | ||||||
|---|---|---|---|---|---|---|---|
|
Received Message |
Active Timing Mode 1 |
DS1 Output State 2 |
Quality Level |
Received Message |
Active Timing Mode 1 |
E1 Output State 2 |
Quality Level |
|
Don't Use (DUS) |
Holdover |
AIS |
9 |
Don't Use (DUS) |
Holdover |
AIS |
5 |
|
Traceable Stratum 4 (ST4) 4 |
Holdover |
AIS |
8 |
NA |
NA |
NA |
NA |
|
Traceable SONET Clock w/S3-TG (SMC) |
OK to use |
Good |
7 |
SDH Equipment Clock |
OK to use |
Good |
4 |
|
Traceable Stratum 3 (ST3) |
OK to use |
Good |
6 |
Synchronization Supply Unit - Type B |
OK to use |
Good |
3 |
|
Traceable Stratum 3E (ST3E) |
OK to use |
Good |
5 |
NA |
NA |
NA |
NA |
|
Traceable Transit Node Clock (TNC) |
Ok to use |
Good |
4 |
Synchronization Supply Unit - Type A |
OK to use |
Good |
2 |
|
Traceable Stratum 2 |
OK to use |
Good |
3 |
NA |
NA |
NA |
NA |
|
Sync Trace Unknown (STU) |
OK to use |
Good |
2 |
NA |
NA |
NA |
NA |
|
PRS Traceable 3 |
OK to use |
Good |
1 |
Primary Reference Clock |
OK to use |
Good |
1 |
This column applies only when provisioned for line timing mode.
This column represents DS1/E1 output AIS threshold equal to level 7 (SONET) and level 4 (SDH).
The oscillator in the VLNC50/52/55 provides an embedded SMC/SEC ±20 ppm.
Telcordia ® has not assigned a value to the S1 byte for ST4.
Alcatel-Lucent 1850 TSS-5 supports the following synchronous Ethernet synchronization status messages as specified in ITU-T G.8264.
When synchronous Ethernet ports are provisioned as the timing sources, the incoming synchronization status messages are used to select the highest quality synchronous Ethernet timing source. When an Ethernet port is provisioned as a synchronous Ethernet port and is not one of the timing sources, the outgoing synchronization status message represent the quality of the timing source for the network element.
Synchronization status messaging can be disabled on a per OC-n/STM-n/Ethernet interface basis.
A DON'T USE message is sent to indicate that its timing is not suitable for synchronization (for example, back towards the line timing source).
When Alcatel-Lucent 1850 TSS-5 is configured for line timing, the DON'T USE message is sent on the OC-n/STM-n interfaces towards the NE from which the timing is being derived. The message received on the OC-n/STM-n interface is sent on all other OC-n/STM-n interfaces where synchronization status messaging is enabled.
With automatic synchronization reconfiguration, the Alcatel-Lucent 1850 TSS-5 shelves receive and compare the incoming synchronization status messages on the OC-n/STM-n/Ethernet interfaces available for line timing to select the highest quality synchronization reference available. If the received quality levels are the same on the references available for timing, the active line timing reference takes precedence. This feature guarantees the non-revertive operation of reconfiguration.
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