 assigned a DID (direct inward dialing) number, that makes it accessible through the PBX. The advantage to this scenario is that the videoconferencing system shares PRI channels on a call-by-call basis with other applications. The disadvantage is that the connection is essentially dedicated and, therefore, results in the same problems with inter-IXC calling that are encountered with other dedicated access methods. ISDN H0, H1 AND MULTIRATE ISDN is designed to allow customers to select different bandwidths easily by combining, on a flexible basis, the number of ISDN B channels necessary to deliver a desired level of motion handling and picture resolution. Today a North American customer can set up a videoconference at 384 Kbps or 1.536 Mbps using a long- distance carrier's HO- and H11-based products. HO and H11 service use several ITU-T protocols for call set-up. These are Q.920, Q.921 and Q.931. Link Access Protocol-D (LAPD) is formally specified in ITU-T Q.920 and ITU-T Q.921. LAPD is an OSI layer-2 protocol. The connection-oriented service establishes a point-to-point D channel link between a customer and a carrier's switch. Data is sent over the link as Q.921 packets. Whereas the D channel is packet- switched, B channel connections are circuit-switched and are established, maintained, and torn down using the Q.931 interface (also known as ITU-T I.451). In Q.931, the ITU-T specified how 'H' channels-multiple contiguous channels on T-1 or E-1/CEPT frames-can be bound together and switched across an ISDN network. In addition to the switched 384 HO standard and the switched 1.536 H11 standard, the ITU-T specifies H12 (European switched 1.920. All are part of Q.931, and all make it possible for high-bandwidth circuits to be created on-demand. The network guarantees end-to-end synchronization and clear-channel access. However, the customer's premise equipment must bond the channels and pass them to the network over PRI access. HO dialing calls for six contiguous DSOs to be combined into a single 384 Kbps channel. At