PM5364 pmc-sierra, PM5364 Datasheet - Page 137

• Manufacturer Part Number: PM5364
• Description: Tupp 2488 Assp Telecom Standard
• Manufacturer: pmc-sierra

Proprietary and Confidential to PMC-Sierra, Inc., and for its customers’ internal use.
Document No.: PMC-2011334, Issue 7
•
Notes on VTPA
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Notes on MSU-Lite
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Two sets of figures are shown in applications where MSU-Lites are used – when the
MSU-Lites are in 1:1 configuration; i.e. data goes out the same order it came in, and when
they are doing extreme switching; i.e. the first tributary in is the last tributary out.
VTPA latency of 19.23 µs for VT1.5 is the steady state delay through VTPA. This will increase
momentarily to a delay of 24.03 µs during negative justification events until the corresponding
negative pointer movement can be performed. Once an incoming negative pointer movement is
detected, VTPA can’t begin an outgoing one until the beginning of the next multiframe (V1 byte) and
the effect of the schedule movement does not take place until the V3 byte.
The above assumes that the aggregate incoming high order and low order justification rate per
tributary is no more than one every four multiframes.
For out of tolerance justification rates (i.e. more than one justification every four multiframes), latency
through VTPA will be more than 24.03 µs.
In the following calculations, the steady state delay of 19.23 µs through the VTPA was used.
Max switching delay of 18.26 µs through MSU-Lite assumes that VT-level switching is being
performed. 18.26 µs corresponds to 1.33 rows of the STS-12 frame. If full column switching is
performed i.e. the order of the columns inside a VT is allowed to change, then max delay through
MSU-Lite would be 26.9 µs i.e. approx 2 rows of the STS-12 frame.
In the following calculations, max delay of 18.26 µs was used through MSU-Lite for MSU switching
configurations.
In the hairpinning case, max delay through one MSU-Lite (1.33 rows) and nominal delay through the
other MSU-Lite (1 row) was used.
TUPP™ 2488 ASSP Telecom Standard Product Data Sheet
Released
137