ISDN interfacesMeridian 1 Networking supports three ISDN interfaces:— Primary Rate Interface (PRI): 30B+D— Primary Rate Interface (PRI): nB+D— ISDN Signaling Link (ISL): nB+D— 2B+D Basic Rate Interface (2B+D BRI)Note: As noted earlier, this document does not contain information onISDN BRI - this is information is contained in theISDN BRIAdministration and Maintenance 553-3011-311.Data TransmissionTypesDTI PRIAsynchronous up to 19.2 kbps up to 19.2 kbpsSynchronous up to 64 kbps up to 64 kbpsChapter 1 — ISDN and DTI Interfaces Page 5 of 1280Option 11C 2.0 Mb DTI/PRI Administration and Maintenance guidePrimary Rate Interface (PRI)Primary Rate Interface is characterized by digital carriers and out-of-bandsignaling. All signaling is done over a D-channel, leaving the remainingB-channels free for voice and data transmission. The D-channel carries all thecall set-up, call tear-down, calling line identification, and feature activationinformation.PRI is referred to as either “30B+D” or “nB+D”. This distinction is based onthe fact that one D-channel can support multiple digital carriers. In otherwords, the choice exists to have one D-channel per digital carrier, or to haveone D-channel support a number of carriers.30B+D Primary Rate InterfaceIn the 30B+D PRI arrangement, each digital carrier (E-1) has its ownD-channel. There are 32 timeslots per E-1 carrier: timeslot zero is reservedfor framing information, timeslot 16 is used as the D-channel, leaving 30channels for voice and data. The B-channels are “clear” channels, meaning all64 K are used for voice and data.The 30 B channels plus one D-channelstructure conforms to the CCITT specification (I.431) for PRI layer 1protocol.Figure 130B+D Primary Rate Interface Structure30B+D PRI30 B Channels@ 64 Kbps1D Channel@ 64 Kbps†Synchronization