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Packet over SDH (POS)
Jitter Tolerance Testing of POS Equipment
Jitter Tolerance Testing of POS Equipment
Jitter is present to a certain extent in all telecommunication networks, and can be
defined simply as the movement in time of parts of a clock or data stream relative to
where we expect to find them. Bit errors or data loss will occur in a digital signal if
jitter at the input port of a network element exceeds a threshold value. It is important
therefore that the network element be designed to tolerate a sufficient level of jitter,
that is, does not introduce errors when certain values of jitter are present. The
ITU-T specifies the lower limit of maximum tolerable input jitter (MTIJ) in the
form of an ITU-T jitter tolerance mask. The OmniBER provides a number of ITU-T
masks for Jitter Tolerance testing, see "Measuring Jitter Tolerance" page 134.
Use the Jitter generation and measurement features of the OmniBER to verify the
jitter tolerance of POS line cards.
Jitter/Wander Generation and Jitter Tolerance and Jitter Transfer tests are available
at all SDH rates when a POS payload is selected.
Automatic Jitter Tolerance measurement is only available with a POS payload when
the payload selected is 2^23-1PRBS.
Only a Jitter Tolerance example is given here, for information on Jitter Transfer and
Wander measurements refer to "Measuring Jitter Transfer" page 138 and
"Measuring Wander" page 131.
Jitter Tolerance method
Jitter is generated at a range of frequencies within the mask and an error
measurement is made. If no errors occur (PASS), the jitter amplitude at that
frequency point is increased until errors occur (FAIL) or the maximum jitter
amplitude is reached. The highest jitter amplitude at which PASS occurs is plotted
on the graph as the Jitter Tolerance for that jitter frequency.
User-Programmable Masks
There are 5 user programmable masks provided allowing you to create, edit and title
up to 5 jitter masks. Please refer to "To Generate a New Jitter Mask" on page 299
and "To change the parameters of a User Defined Jitter Mask" on page 301 for
instructions on how to generate or edit a user programmable mask.
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