Sync messaging feature details and options

Overview

As mentioned previously, SONET sync messaging is used to communicate the quality of the subnetwork timing throughout the subnetwork. This is done using the S1 byte in the SONET or SDH overhead and is supported in the DS1 or E1 external timing reference inputs and outputs. If an Alcatel-Lucent 1665 DMX shelf is deriving timing from a given OC-n interface, and sync messaging is enabled on that interface, the system interprets the received message to determine the system's timing status. The system also determines the state of the DS1 output, if the DS1 output is enabled, by forcing a DS1 AIS on the DS1 sync outputs if the timing status received on the OC-n interface is below a provisioned quality threshold. Alcatel-Lucent 1665 DMX also supports E1 timing output when equipped with a VLF Main circuit pack.

Alcatel-Lucent 1665 DMX also transmits over the particular OC-n interface, and all other OC-n interfaces that are enabled for sync messaging, the appropriate message indicating the quality of its timing and its usability.

Important!

When the Alcatel-Lucent 1665 DMX is provisioned for SONETSYNC, both input ext timing reference and ext refrence output are DS1. When the Alcatel-Lucent 1665 DMX is provisioned for SDHSYNC, both input ext timing reference and ext reference output are E1.

Sync messages using S1 byte

The following table lists the associated internal timing status and DS1/E1 output states that are associated with sync messages (using the S1 byte) received from the OC-n interface when sync messaging is enabled. The same parameter used to choose between DS1 and E1 timing outputs is employed to choose between SONET sync messaging and SDH sync messaging. Messages are listed from low to high quality.

Table 6-19: Sync Messages with the S1 Byte

SONET				SDH
Received Message	Active Timing Mode¹	DS1 Output State²	Quality Level	Received Message	Active Timing Mode¹	E1 Output State²	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)	Holdover	AIS	7	DSH Equipment Clock	Holdover	AIS	4
Traceable Stratum 3 (ST3)³	OK to use	AIS	6	Synchronization Supply Unit - Type B	OK to use	AIS	3
Traceable Stratum 3E (ST3E)	OK to use	AIS	5	NA	NA	NA	NA
Traceable Transit Node Clock (TNC)	Ok to use	AIS	4	Synchronization Supply Unit - Type A	OK to use	AIS	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 Traceable³	OK to use	Good	1	Primary Reference Clock	OK to use	Good	1

Notes:

This column applies only when provisioned for line timing mode.
This table represents DS1/E1 output AIS threshold equal to level 4.
The embedded TG3 is Stratum 3.
Telcordia ^® has not assigned a value to the S1 byte for ST4.

Disabling sync messaging

Sync messaging using the SONET S1 byte can be disabled on a per OC-n interface basis. A Don't Use for Service (DUS) message is transmitted on bits 5–8 of the S1 byte if this is done.

"Don't use" (DUS)

The DUS message is sent to indicate that its timing is not suitable for synchronization (for example, back towards the line timing source).

External timing with SYNC OUT

When Alcatel-Lucent 1665 DMX is configured for external timing and its DS1/E1 output port is provisioned for the SYNC OUT mode, the DUS is sent on the OC-n interface towards the NE from which the DS1/E1 timing output is being derived. The Synchronized - Traceability Unknown (STU) message is sent on all other OC-n interfaces where sync messaging is provisioned. If the DS1/E1 output is generating AIS while the system is configured in this way, the message STU is transmitted on all OC-n interfaces.

TG3 with free running or holdover

When using the embedded TG3, if Alcatel-Lucent 1665 DMX is configured for free running or is in holdover mode, the Traceable Stratum 3 message is sent on all OC-n interfaces for which sync messaging is enabled.

Line timing

When Alcatel-Lucent 1665 DMX is configured for line timing, the DUS message is sent on the OC-n interface towards the NE from which the timing is being derived. The message received on the OC-n interface is sent on all other OC-n interfaces where sync messaging is enabled.

Automatic synchronization reconfiguration

With automatic synchronization reconfiguration, the Alcatel-Lucent 1665 DMX shelves receive and compare the incoming sync messages on the OC-n 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. Although a revertive option is supported.

The existence of automatic synchronization reconfiguration does not affect OC-n line protection switching.

Hitless timing and equipment switching

Hitless timing equipment switching enables switching from an active timing generator (TG) on one Main circuit pack to the TG on the other Main circuit pack without incurring transmission hits on any of the Main, Function Unit, or Growth circuit packs. This feature is only available on the VLF Main packs (LNW59/LNW82/LNW504). Low-speed, tributary OLIUs that allow hitless timing switching include the following: LNW45, LNW49, LNW55. DS1 & DS3 signals/cards are asynchronous, and are not affected by a timing switch. Ethernet packs are also unaffected.