PXB4219 Datasheet, PDF (277/290 Pages) Infineon Technologies AG – IWE8 Interworking Element for 8 E1/T1 Lines

PXB4219 / PXB4220 / PXB4221
Appendix
Fast Sequence Count Algorithm
The state machines of the robust SC algorithm and the fast SC algorithm are the same.
The only difference is that in the fast algorithm, the action to be taken always refers to
the currently received cell, while in the standard algorithm it refers to the temporarily
stored cell. Therefore the fast SC algorithm does not introduce additional one-cell delay.
In the fast SC algorithm, a misinserted cell is immediately accepted in the reassembly
buffer. Only at the arrival of the next cell, it is detected that the previous cell was
misinserted. Because the misinserted cell was already accepted, the current (in
sequence) cell will be discarded instead. Lost cells are compensated with the insertion
of dummy cells as in the standard algorithm.
Frequency and Value of the Pointer Field
The pointer field contains the binary value of the offset, measured in octets, between the
end of the pointer field and the start of the structured block, in the 93 octet payload. The
payload consists of the remaining 46 octets of this SAR-PDU payload and the 47 octets
of the next SAR-PDU payload.
The frequency of occurrence of the pointer field is according to ITU-T I.363.1 [31]. The
pointer field is used exactly once in every cycle, where a cycle is the sequence of eight
consecutive SAR-PDUs with Sequence Count values 0, 1, to 7. The pointer field is used
at the first available opportunity in a cycle to point to a start of a structured block. If a start
of a structured block is not present in a cycle, then a pointer field containing a dummy
offset value ‘127’ is used at the last opportunity in the cycle.
Data Sheet
277
2002-05-06