bandwidth. PRI uses out-of-band signaling, and thereby results in a pipe with 23 B channels (each of which offers 64 Kbps of bandwidth) and one 64 Kbps D channel. An ISDN PRI customer has exclusive use of the 23 B channels, which can be used separately or aggregated for data transport. Although PRI B channels are used for video and data conferencing, it is not common to dedicate an entire ISDN PRI pipe to a single videoconferencing system. In both PRI and BRI arrangements, the ISDN D channel extends the intelligence of a carrier's SS7 network beyond historic boundaries, and allows it to communicate with customer premise equipment. The customer and the carrier can share the D channel, (e.g., the customer can transmit packet-switched data over it) however this is very rare. PRI terminates in a network terminal device called an NT-2. The NT-2 provides the same functions for ISDN PRI service as the NT-1 provides for BRI lines. In addition, the NT-2 performs switching (to route individual B channels) and bonding (to aggregate them into Nx64 pipes). Although it is not always possible to access BRI from a LEC, ISDN PRI is generally available from an IXC. PRI is used for many things, including inbound and outbound long distance, remote LAN access, and videoconferencing. A PRI pipe typically terminates in a PBX or an ISDN hub. Switched 384, 1536 HO, H11 One DS1 frame One H11 channel One HO channel ISDN H channels are dfined as multiple contiguous channels on a DS1 frame End-to-end data ordering and continuity are guaranteed by the network ISDN PRI required to access H-channel service Source: Jay Duncanson-Ascend Communications Figure 11-4. Switched 284, 1536 (HO, H11) Framing (Michael Bayard). In an ISDN-enabled PBX environment, the PRI comes in to the trunk side of the switch (the side leading to the telephone company) and video communication CPE hangs off the station side. To make a video call, a station goes off-hook (perhaps Circuit-switched Networks using software) and dials a number. If there are ISDN B channels ava