Alcatel-Lucent 1643 AMS - Timing quality levels

Timing quality levels
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Introduction
To choose the most appropriate timing signal from all the incoming timing signals, the
quality of the timing signals must be known.
Different quality levels are defined for timing signals. The quality levels specify the
quality of the incoming or outgoing timing signal. The quality levels are related to the
equipment used to produce the corresponding timing signal.
Accuracy
The accuracy of a timing signal can be given in an accuracy value. Every timing signal
will have an average frequency, and a deviation in time from the average frequency
value. The deviation from the average frequency, can be represented as a fraction of
the average frequency. This fraction is known as the accuracy value.
Example
When a timing reference has an average frequency of 2048 MHz, and varies in time
between 2048.01 MHz and 2047.99 MHz, the deviation from the average value is plus
or minus 0.01 MHz. This can be expressed in an accuracy value:
Accuracy = 0.01 / 2048 = 0.0000049 = 4.9 x 10
-6
Quality levels
The quality level (QL) values are transported as a synchronization status message in
the S1 Byte in the STM-N signal or in the 4th position of the Sa-bit in a framed 2
Mbit/s signal.
QL S1-byte Accuracy Description
Quality
Unknown
S1=0 N/A No QL information of the signal is available.
PRC S1=02 10
-11
Primary Reference Clock indicates that the timing signal
is provided by a Primary Reference Clock.
SSU-T S1=04 1.5 x 10
-9
Synchronization Supply Unit-Transit indicates that the
timing signal is derived from a Transit SSU
SSU-L S1=08 3 x 10
-8
Synchronization Supply Unit-Local indicates that the
timing signal was derived from a Local SSU
SEC S1=11 4.6 x 10
-6
SDH Equipment Clock indicates that the timing signal is
provided by an SDH Equipment Clock.
DNU S1=15 N/A Do not use for synchronization indicates that the timing
signal should not be used, since it may cause timing
loops.
Timing provisioning
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365-312-807R7.2
Issue 4, May 2007
Alcatel-Lucent - Proprietary
See notice on first page
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