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6.2 THE GR-303 STANDARD 131TABLE 6.1-1 Access Systems Terminology MapCommon Term GR-303 V5Access system (AS) Remote digital terminal (RDT) Access network (AN)Local exchange (LE) Local digital switch (LDS) Local exchangeDigital trunk interface in the LE Integrated digital terminal (IDT) Exchange termination(ET)The complex of AS, transmission Integrated digital loop carrier (not used)facilities, and LE terminations (IDLC)An individual TS in a DS1 line DS0 64-kb/s Time slotTime-slot assignment Time-slot assignment Time-slot allocationVoice channel aTS assigned to a subscriberlineBearer channela A voice channel can carry user data other than voice, but voice is the most common use.Both protocols use the concepts of common-channel signaling (Chapter 5) andlayers (Chapter 20), which are necessary for a full understanding of the sectionsthat follow. The reader unfamiliar with those concepts is referred to the correspondingchapters of the book.Terminology. The terminology used in the Telcordia interface standards is differentfrom the terminology used in the ITU-T recommendations. For ease of understanding,this chapter uses the standard telecommunications terms found in therest of the book. Table 6.1-1 provides a map of the different terms.6.2 THE GR-303 STANDARDGR-303 (formerly TR-303) is the North American standard for access interfaces [1].The standard supports:. Both fixed and dynamic TS assignment. Analog subscriber lines. ISDN subscriber lines (2B þ D and 23B þ D). 1to28T1/DS1 digital links per GR-303 interface. SONET optical links. Protection switching for multilink configurationsChannels. Most time slots (DS0) in a digital link are used as voice channels thatcan be assigned to subscriber interfaces; a few are used as signaling and OAM channels.There are two types of signaling channels:. Common signaling channel. Channel-associated signaling subchannels