MT90520AG ZARLINK [Zarlink Semiconductor Inc], MT90520AG Datasheet - Page 76

• Manufacturer Part Number: MT90520AG
• Description: 8-Port Primary Rate Circuit Emulation AAL1 SAR
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

SDT Mode of Operation
The SDT version of the Fast Sequence Number Checking state machine is very similar to the UDT version.
However, in the SDT version, no extra states are added for increased functionality. Unlike the UDT version, there is
no provision for the insertion of dummy cells in late-cell cases, nor for in-order dummy cell insertion when single-cell
losses are assumed. Because the SDT machine has fewer states than the UDT version, there are some differences
in the way in which certain cell arrival sequences are interpreted by the state machines. The following table outlines
the operation of the SDT state machine:
Sequence number protection
failure (looks like multiple cell
loss)
Single lost cell
Multiple lost cells (from 2 to 7
lost cells)
Misinserted (swapped) cell
NOTE: D indicates the insertion of a dummy cell containing user-programmable data.
Table 16 - Examples of Operation of the UDT Fast Sequence Number Processing State Machine
Description of Error
x (don’t care)
reset_state
start
out_of_sync
sync
invalid
Current State
Table 17 - Operation of SDT Fast Sequence Number Processing State Machine
reset de-asserted
valid sequence number
invalid sequence number
received cell is not in sequence with previous
cell
received cell is in sequence with previous cell
invalid sequence number
received cell is not in sequence with the
previously-received cell
received cell is in sequence with previous cell
received cell is in sequence with last “good”
cell (i.e., cell misinsertion)
received cell has a valid sequence number
that is two greater than the last “good” cell
(i.e., sequence number protection failure)
received cell has valid sequence number, but
doesn’t meet either of the 2 previous criteria
reset asserted
invalid sequence number
invalid sequence number
Sample Incoming Cell
Transition Event
1 - 2 - 4 - 3 - 5 - 6
1 - 4* - 3 - 4 - 5
1 - 2 - 4 - 5
1 - 2 - 6 - 7
Stream
Zarlink Semiconductor Inc.
MT90520
76
1 - 2 - 6 - D
1 - 2 - D
- none
- none
- discard cell
- discard cell
- discard cell
- discard cell
- accept received cell
- accept received cell
- accept received cell
- declare aal1_seq_error
- accept received cell
- permit SDT RX_SAR to update
CAS information based on this
cell’s contents
- discard cell
- discard cell (because misinserted
cell was accepted when it shouldn’t
have been)
- declare misinserted_cell_error
- accept received cell
- discard cell
Cells Used for
1 - 2 - D
1 - 4* - 3 - 4 - 5
Reassembly
3
3
3
- 4 - 5 - 6
- D
Action Taken
- 4 - 5
4
- D
5
- 7
1 AAL1 Sequence Error
1 AAL1 Sequence Error
1 Lost Cell
1 AAL1 Sequence Error
3 Lost Cells
1 AAL1 Sequence Error
1 Misinserted Cell
Errors Declared
reset_state
start
start
out_of_sync
start
out_of_sync
sync
invalid
out_of_seq
sync
start
sync
sync
out_of_sync
Next State
Data Sheet