28236-DSH-001-B Datasheet, PDF (86/443 Pages) M/A-COM Technology Solutions, Inc. – ATM ServiceSAR Plus with xBR Traffic Management

4.0 Segmentation Coprocessor
4.2 Segmentation Functional Description
CN8236
ATM ServiceSAR Plus with xBR Traffic Management
4.2.3 CPCS-PDU Processing
4.2.3.1 AAL5
The buffers submitted by the user contain only user data, the CPCS Service Data
Unit (CPCS-SDU). The CN8236 adds the CPCS-PDU protocol fields to the
CPCS-SDU. The SAR supports three AAL levels: AAL5, AAL3/4, and a
transparent adaptation layer (AAL0).
Specific features also allow the generation of OAM cells. Chapter 7.0, covers
OAM generation in detail.
For AAL5, the SAR generates the CPCS-PDU trailer and pads the CPCS-SDU to
align the PDU to a cell boundary. The CN8236 generates the PAD, Length (LEN),
Common Part Indicator (CPI), and Cyclic Redundancy Check (CRC) fields
according to I.363. The host supplies the CPCS User-to-User Indication (UU)
field in the first buffer descriptor in a message, and the CN8236 transmits it
following I.363.
The SAR generates the ATM header according to host-initialized settings in
the VCC table entry. The CN8236 terminates AAL5 PDUs by setting bit 0 of the
Payload Type Identifier field, PTI[0] = 1.
The host aborts PDUs by activating an EOM SBD abort option. The host
activates this by setting the following fields in the SEG buffer descriptor entry to
these values: AAL_MODE = AAL5 (b00), and AAL_OPT = ABORT (b01).
Figure 4-5 illustrates the CN8236’s AAL5 PDU generation scheme. The SAR
uses internal circuits to generate and store PDU length and CRC-32 in the SEG
VCC table. The CN8236 transmits these fields within the EOM cell. The PAD
and CPI fields are generated internally.
Figure 4-5. AAL5 CPCS-PDU Generation
USER DATA BUFFER(S)
H
H
TX_FIFO
(1-9 Cells)
PHY Interface
Internal
Byte Length Counter
CRC Accumulator
Circuits
H
PAD UU CPI LEN CRC-32
(Set PTI[0] = 1)
UU
ATM_HEADER
PDU_LEN
CRC_REM
SEG VCC Table Entry
8236_016
4-8
Mindspeed Technologies™
28236-DSH-001-B