MPC8280 datasheet(1063/1386 Pages) FREESCALE

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ATM AAL1 Circuit Emulation Service

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

32-3

32.2

AAL1 CES Transmitter Overview

The MPC8280 supports both structured and unstructured AAL1 cell formats. For unstructured format, the

transmitter reads 47 bytes from the external buffer and inserts them into the AAL1 user data field. For

structured format, the transmitter reads 46 or 47 bytes from the external buffer and inserts them into the

AAL1 user data field.

32.2.1

Data Path

The AAL1 PDU header, which consists of the sequence number (SN) and the sequence number protection

(SNP) (CRC-3 and parity bit), is generated and inserted into the AAL1 Tx cell, as shown in Figure 32-1.

Figure 32-1. AAL1 Transmit Cell Format

When the transmitter operates in structured data transfer (SDT) mode, two types of AAL1 cells are

defined: P (pointer) format and non-P format. The two formats are shown below.

Figure 32-2. AAL1 SDT Cell Types

The transmitter generates the structured pointer according to the I.363.1 ITU standard and inserts the

pointer exactly once every cycle (eight successive cells). The transmitter will insert the structured pointer,

at the first opportunity, into a cell with an even sequence count (SC). When the end of the structure is not

present in the current cycle, a P-format cell with a dummy pointer (127) is inserted into the last cell (SC=6)

of the cycle.

The MPC8280 supports partially filled cells configured on a per-VC basis. In this mode, only the valid

octets are filled with user information; the rest of the cell is filled with padding octets.

The MPC8280 supports synchronous residual time stamp (SRTS) generation using an external PLL. If this

mode is enabled, the MPC8280 reads the SRTS code from external logic and inserts it into four outgoing

cells. See Section 31.16, “SRTS Generation and Clock Recovery Using External Logic.”

32.2.2

Signaling Path

The MPC8280 automatically handles the signaling information as part of the interworking function. The

ATM transmitter packs the signaling information at the end of each superframe during the data

segmentation process. Each VC is associated to one signaling block by an internal routing table; see

SNP

SAR-PDU payload

SAR PDU header

SAR-PDU header

ST pointer

AAL1 user information

P format AAL1 cell

Non-P format AAL1 cell

SAR-PDU header

AAL1 user information

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