
IWE8, V3.4
PXB 4219E, PXB 4220E, PXB 4221E
Operational Description
Data Sheet
44
2003-01-20
If idle cell insertion according to ITU-T I.361 or ITU-T I.432.1 is desired, the
“prg_tx_hd” field of “txid” should be set to 0000_0001
B
.
If unassigned cell insertion at the NNI or uncontrolled UNI according to ITU-T I.361 is
desired, the “prg_tx_hd” field of “txid” should be set to 0000 XXX0. For X any value is
allowed.
The payload of idle or unassigned cells consists of the same octet which is repeated 48
times. It is programmable by the “prg_tx_pl” field of the “txid” register.
For ITU-T I.432.1 compliant idle cells, the “prg_tx_pl” field of “txid” should be set to
0110_1010
B
.
The pre-assigned values of the information field of all unassigned cells are for further
study (ITU-T I.361 [30])
4.1.1.4
ITU-T I.432.3 [34] recommends the self-synchronizing scrambler x
43
+1 for payload
scrambling at E1 datarates. For T1 no scrambling is recommended, which the IWE8
supports.
The scrambler function is implemented in the device. It can be disabled per port by the
x43_scrambling bit in the “ATM Transmit Reference Slot” in RAM2.
Cell Payload Scrambling
4.1.1.5
HEC Generation
The HEC generation is implemented according to ITU-T I.432.1 [33] using the generator
polynomial x
8
+ x
2
+ x + 1. To significantly improve the cell delineation performance in
the case of bit-slips it is recommended that
the check bits are added (modulo 2) to an 8-bit pattern (coset) before being inserted
in the last octet of the header.
the recommended pattern is “0101 0101".
octet 1
octet 2
octet 3
octet 4
GFC[3:0]/VPI[11:8] = prg_tx_hd[7:4]
VPI[3:0] = 0000
B
VPI[7:4] = 0000
B
VCI[15:12] = 0000
B
VCI[11:4] = 0000_0000
B
VCI[3:0] = 0000
B
PTI[2:0] = prg_tx_hd[3:1]
CLP =
prg_tx_
hd[0]
octet 5
octet 6
.
octet 53
UDF
prg_tx_pl[7:0]
.
prg_tx_pl[7:0]