ards AMLn model of a B-ISDN SAAL node DSS2 L3 MTP-3b MTP-3b DSS2 L3 SSCF-UNI SSCF-NNI SSCF-UNI Service Specific Service Specific Q.2130 Q.2110 coordination coordination SSCOP function function SSCF-NNI ITU-TQ.2130 ITU-TQ.2140 Q.2140 1.363.5 AAL5- SSCOP Service Specific Coordination Oriented Protocol VCI=2, 5 ITU-T Q.2110 VPI=many ITU-T Q.2100 ATM stratum AAL5-CPCS Comment: Common Part The allocation to Q. and I. standards series indicates Convergence what is specific for the service delivered by the AAL (Q.) Sublayer and what is specific for a class of AAL services (I.) ITU-T 1.363.5 Note also that the present version of Q.2100 AAL5-SAR refers standards (1.362 and 1.363) that do no Segmentation and longer exist (withdrawn). Reassembly Sublayer *) Emulates SS7 signalling links (MTP L2) Emulates LAPD connections See ITU-T Q.2210 ATM stratum Fig. 6.16 The signaling AAL (SAAL) that is used for supporting B-ISDN control protocols SSCF is a generic term for actor functions that adapt the connectivity service of an AAL to layer interfaces that are used by existing layers. In this model, the SAAL supports layers of the B-ISDN service control stratum, i.e., B-ISUP and DSS2 L3. For the use of DSS2 L3, the SSCF-UNI actor provides a LAPD-like layer inter- face. Since SSCOP performs basic link layer functions, stratum 6 Applying AMLn provides the correspondence to LAPD connections, the SSCF-UNI does not do much more than defining a standardized interface. B-ISUP is assumed to use ordinary SS7 interfaces, i.e., MTP L3 and SCCP, in order to be able to interwork with N-ISDN networks. The SSCF-NNI actor is therefore designed to act as the correspondence to an MTP L2-type of layer. Note that a reduced variant of the MTP L3 is defined (called MTP-3b, see ITU- T Q.2210), to be used by the B-ISUP agent layer. The MTP-3b defines a reduced variant of the MTP L3 protocol and maps MTP L3 addressing parame- ters (e.g., DPC, OPC) on the VPI/VCI parameters. Other SS7 adaptation layers exist as well, e.g., for providing SCCP interfaces. Note