MPC8280 datasheet(1108/1386 Pages) FREESCALE

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ATM AAL2

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

33-2

Freescale Semiconductor

AAL2 is subdivided into two sublayers, as shown in Figure 33-2:

•

Common part sublayer (CPS)—In the CPS sublayer, variable length packets coming from multiple

users are assembled into CPS-PDUs belonging to a single ATM VC.

•

Service-specific convergence sublayer (SSCS)—The SSCS sublayer handles the mapping of user

data to the CPS sublayer. The SSCS segments large data frames into smaller CPS packets and also

provides different services to the user, such as transmission error detection. The SSCS sublayer is

further divided into three service-specific layers:

— Service-specific segmentation and reassembly sublayer (SSSAR)

— Service-specific transmission error detection sublayer (SSTED)

— Service-specific assured data transfer sublayer (SSADT)

Figure 33-2. AAL2 Sublayer Structure

The AAL2 microcode implements the CPS and SSSAR sublayers. (The SSADT and SSTED sublayers are

not implemented.) As shown in Figure 33-2, the user can access the CPS sublayer directly or through the

SSSAR sublayer. The SSSAR sublayer is used mainly for transferring large data frames.

The AAL2 microcode also enables switching from one PHY | VP | VC | CID combination to another; an

example is shown in Figure 33-3.

Common part sublayer

Service specific segmentation & reassembly

Service specific transmission error detection

Service specific assured data transfer

SAP

User

SSCS

CPS

AAL2

SSTED

SSSAR

SSADT

User

(SAP): Service access point

CPS

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