SAAL - Signalling ATM Adaptation Layer

An AAL that provides reliable transport of signalling messages (Q.2931)
between peer Q.2931 entities.  These signalling messages are carried over
a PVC. Currently, the signalling VC is defined (in the ATM Forum, at
least) to be a PVC with VPI = 0 and VCI = 5. 

The SAAL consists of the following:

+--------------------+
|       SSCF         |
| ------------------ | SSCS
|       SSCOP        |
+--------------------+
|       CPCS         |
+--------------------+
|       SAR          |
+--------------------+

SSCOP is a general purpose data transfer layer providing, among other
things, assured data transfer.

SSCF is a coordination function that maps SSCOP services into those
primitives needed specifically for signalling (by Q.2931). Different
SSCFs may be prescribed for different services using the same SSCOP.

The SSCS may be null as well (e.g. IP-over-ATM or LAN Emulation).




AAL    - ATM Adaptation Layer
PVC    - Permanent Virtual Channel
Q.2931 - Formally Q.93B. See entry elsewhere in this dictionary
SAR    - Segmentation and Reassembly
VC     - Virtual Channel
VCI    - Virtual Channel Identifier
VPI    - Virtual Path Identifier