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6.6 ACRONYMS 153in the table. The User Port Identification IE identifies the analog line or ISDN port towhich the message is related: for PSTN lines it uses the same 15-bit values as L3addrin the PSTN L3 protocol, and for ISDN lines the same 13-bit values as the EFaddr inthe LAPV5-EF sublayer. The ISDN Port TS Identification IE identifies theB-channel that needs to be connected to a TS (e.g., channel B1 or B2 of a basicrate interface or channel 1 through 31 of a primary rate interface). The V5 TimeSlot Identification IE identifies the digital link and the TS in that link that is assignedto the user interface. The Multislot Map IE is used when allocating blocks of TSs toH-channels (n 64 kb/s).Call Sequences. Examples of call sequences are shown in Figs. 6.5-2 and 6.5-3.In the case of ISDN calls, two allocation processes, both controlled by the LE, takeplace: B-channels are assigned to the call and TSs to B-channels. The first allocation(B- or H-channel assignment, e.g., B1 or B2) is part of standard ISDN call-setupprocedures (Section 10.4.2); the second is specific to V5.2. Both allocations arecommunicated by the LE to the AS in a BCC message, but the first is also sentfrom the LE directly to the ISDN customer-premises equipment in a D-channelmessage. B-channel identification is contained in the Channel Identification IE,which for LE originations is carried in the Setup message, and for AS originationsis carried in the response to the Setup message (e.g., Alerting or Call Proceeding).6.6 ACRONYMSANAccess networkAN-FR Access network frame relayASAccess systemBABasic accessBCCBearer Channel ControlBRABasic rate accessCConditionalCCCClear channel connectionC-channel Communication channelCSCCommon Signaling ChannelDS0 Digital signal level 0DS1 Digital signal level 1DSS1 Digital Subscriber Signaling System No. 1DTMF Dual-tone multi frequencyEOCEmbedded Operations ChannelESFExtended superframeETExchange terminationETSIEuropean Telecommunications Standards InstituteFCSFrame check sequenceIDIdentityIDLC Integrated digital loop carrier