mt90503 Zarlink Semiconductor, mt90503 Datasheet - Page 62

• Manufacturer Part Number: mt90503
• Description: 2048vc Aal1 Sar
• Manufacturer: Zarlink Semiconductor

4.3.3
The TX_SAR out-of-bandwidth error indicates that a particular region of the scheduler, or the scheduler as a whole,
is overloaded. This error occurs when the TX_SAR lagging by F frames or more, where F is an integer written to
register 0608h. The TX_SAR has 125 s to execute all the events in the frame it is servicing at the current time. If
all the events in the frame are not executed within 125 s, the TX_SAR continues until the end of the current frame
before moving on to events in the next frame. This method reduces the amount of time it has to service the
following frame. If the first frame took 150 s to service, then there would only be 100 s left to service the following
frame. Therefore, if the second frame is also very full, the TX_SAR would not have the time to finish servicing it and
will be late again for the following frame.
If frames take an excessively long time to service, the MT90503 may become several frames late. If the MT90503
detects that it is F or more frames late, an out-of-bandwidth error will be declared and the MT90503 will skip the
next F frames of events. This action will cause latency in the transmission delay and corrupt data on the VCs until
the channel reconverges. The channel reconverges once every 375 frames (47 ms) in “AAL1 with pointer”
schedulers, and less often if multiframing is used. The cells that were supposed to be assembled in the F missing
frames are skipped, and new cells are assembled with the old data. The out-of-bandwidth error arises from an error
Out of Bandwidth Error
Frame 0
Frame 1
Frame 0
Frame 1
Frame 0
Frame 1
Frame 2
Figure 27 - Partially Synchronised Schedulers
Figure 25 - Unsyncrhonised Schedulers
Figure 26 - Synchronised Schedulers
Scheduler 0
Scheduler 0
23 Events
Scheduler 0
6 Events
20 Events
27 Events
26 Events
15 Events
32 Events
Zarlink Semiconductor Inc.
MT90503
Frame 0
Frame 1
62
Frame 0
Frame 1
Frame 0
Frame 1
Frame 2
Frame 3
Scheduler 1
17 Events
24 Events
Scheduler 1
Scheduler 1
21 Events
12 Events
16 Events
9 Events
5 Events
7 Events
Data Sheet