MT90528AG ZARLINK [Zarlink Semiconductor Inc], MT90528AG Datasheet - Page 58

• Manufacturer Part Number: MT90528AG
• Description: 28-Port Primary Rate Circuit Emulation AAL1 SAR
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

4.5
The TX_SAR modules of the MT90528 device (consisting of the CBR-handling TX_SAR and the non-CBR Data
TX_SAR) are primarily responsible for organizing TDM data into ATM cells. Since the cells contain constant-bit-rate
traffic, they must be assembled at a rate which is synchronized to the 28 plesiochronous TDM ports.
The TX_SAR generates AAL1 cells which may contain TDM data and CAS signalling information. In both the UDT
and SDT modes of operation, the TX_SAR is capable of inserting SRTS clock recovery information into outgoing
cells.
A secondary Data TX_SAR transfers non-CBR cells from a CPU-accessible cell buffer in external memory to the
UTOPIA interface for transfer onto the ATM network.
4.5.1
As mentioned above, the TX_SAR is responsible for the generation of AAL1 cells, in accordance with the formats
set out in ITU-T I.363.1. There are two basic cell formats which are used in AAL1 systems: cells with pointers (used
only in the Structured Data Transfer mode of operation) and cells without pointers (used in both the UDT and SDT
modes of operation). When operating in the 8-bit UTOPIA mode of operation, AAL1 cells are 53 bytes long; when
using the 16-bit UTOPIA mode of operation, AAL1 cells are 54 bytes long and feature an extra field, UDF2. The
formats of the cell types are shown below in Figure 19. Note that the 46-byte or 47-byte payload in the cells may
contain TDM data or CAS signalling information.
TX_SAR Module
ATM Overview
Parity
Even
CSI
8
UDF2 (used only in 16-bit UTOPIA mode)
GFC / VPI
7
Sequence
VCI
VPI
Cell with Pointer
46 Payload Bytes
Count
6
Payload Byte #45
Payload Byte #46
Payload Byte #1
Payload Byte #2
HEC (UDF1)
5
Pointer
VCI
4
Figure 19 - AAL1 ATM Cell Formats
PTI
CRC
field
3
VCI
VPI
Zarlink Semiconductor Inc.
2
Parity
Even
CLP
MT90528
1
58
CSI
8
UDF2 (used only in 16-bit UTOPIA mode)
GFC / VPI
7
Cell without Pointer
VPI
VCI
Sequence
47 Payload Bytes
Count
6
Payload Byte #2
Payload Byte #46
Payload Byte #47
Payload Byte #1
Payload Byte #3
HEC (UDF1)
5
VCI
4
PTI
CRC
field
3
VPI
VCI
2
Parity
Even
CLP
1
Data Sheet