Avaya S8700 Maintenance Manual page 963

ATM-NTWK (ATM Network Error)
If only cell overruns occur, locate the ATM board generating those cells.
Execute test board long. If the board passes, then the ATM network
remains the likely cause of transmission problems. Consult the ATM
network vendor. Ask about cell delay variation, cell discard, and traffic
policing.
h. Error Type 1793 — ATM lost cells:
The ATM board receiving the CBR cell stream is detecting out-of-sequence
AAL1 sequence numbers, above the defined threshold. This normally
indicates that the ATM network has lost the missing cells. In this case,
"lost" could mean that the cells were, for example, policed out, lost to
congestion, or misdirected to another endpoint.
The likely user-visible symptoms of lost cells are missing talk paths or poor
voice quality.
The "lost cells" error can help you diagnose cell underrun problems. When
cell underruns are accompanied by lost cells errors, the lost cells could
have caused the underruns. But if you have cell under runs without lost
cells, it could indicate that the underruns were due to network jitter instead.
It is also possible that network jitter can cause both cell underruns and lost
cells, if the jitter is so severe it causes the cells to violate their traffic
contract.
When accompanied by congestion or CLP errors, the congestion or CLP
can be causing the lost cells.
When accompanied by cell overrun errors, the cell overruns can be
causing the TN2305 to discard cells, which in turn can show up as lost
cells.
Lost cells without other errors can indicate that cells are being corrupted,
especially the AAL1 sequence number.
In any case, consult your ATM network vendor about possible causes.
Look for jitter (cell delay variation), cell discard, and traffic policing.
555-233-143 Issue 1 May 2002 8-241