Freescale Semiconductor MPC8260 - Manual (Page 1064)

ATM AAL2
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
32-2 Freescale Semiconductor
AAL2 is subdivided into two sublayers, as shown in Figure 32-2 :
• 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 32-2. AAL2 Sublayer Structure
The AAL2 microcode implements the CPS and SSSAR sublayers. (The SSADT and SSTED sublayers are
not implemented.) As shown in
Figure 32-2 , 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 32-3 .
Common part sublayer
Service specific segmentation & reassembly
Service specific transmission error detection
Service specific assured data transfer
SAP
SAP
SAP
SAP
User User User
SSCS
CPS
AAL2
SSTED
SSSAR
SSADT
User
(SAP): Service access point
CPS