PXB4219E Datasheet, PDF (274/290 Pages) Infineon Technologies AG – Interworking Element for 8 E1/T1 Lines

12
Appendix
IWE8, V3.4
PXB 4219E, PXB 4220E, PXB 4221E
Appendix
12.1
ATM Adaptation Layer 1
The ATM Adaptation Layer 1 (AAL1) consists of two sublayers: The Segmentation and
Reassembly Sublayer (SAR), which is responsible for sequence integrity of the
transmitted ATM cell stream and the Convergency Sublayer, responsible for blocking of
user data into 47-octet SAR boundaries.
Figure 74 gives an overview on the AAL1 frame-structure as defined in ITU-T I.363.1
[31].
Parity Pointer
1 bit
7 bit
AAL user info
N octets
Dummy Fill
P format P
1 octet
User information
46 octets
CS-Sublayer
Non-P format
User information
47 octets
CSI SC
1 bit 3 bit
CRC Py
3 bit 1 bit
SN SNP
1 octet
SAR-SDU
47 octets
ATM Header
5 octets
ATM-SDU = SAR-PDU
48 octets
Pointer
CSI
SC
CRC
Py
SN
SNP
SAR
SDU
PDU
= octet offset of data block over 2 cells (111 1111 if not required)
= Convergency Sublayer Indication
Non-P Format: CSI = 0
P format:
CSI = 1 if SC = 0,2,4 or 6, P-field may be inserted
CSI = 0 if SC = 1,3,5 or 7, P-field is unused (Non-P format used)
= Sequence Count
= Cyclic Redundancy Check
= Even Parity bit
= Sequence Number incremented by 1 modulo 8 for each SAR-SDU
= Sequence Number Protection
= Segmentation & Reassembly
= Service Data Unit
= Protocol Data Unit
Figure 74 Structure of the AAL1 SAR-PDU
SAR-Sublayer
ATM Layer
Aal1
Data Sheet
274
2003-01-20