minating the need for a channel bank. CSU/DSU CSU stands for Channel Service Unit, and DSU stands for Data Service Unit. A CSU is responsible for interfacing with the WAN link, and a DSU is responsible for interfacing with data equipment such as routers. A CSU/DSU combines these functions into a single unit. Typically, an RJ-45-terminated cable will connect the demarc to the CSU/DSU, and a V.35 cable will connect the CSU/DSU to a router. The CSU/DSU is usually configurable to support all the common T1 sig- naling and framing options. Modern Cisco routers support WAN interface cards (WICs) that have integrated CSU/DSUs. CPE is short for customer premises equipment (i.e., equipment that is located at the customer's premises). Examples might include a PBX, phones, routers, and even cable modems. Traditionally, the term was used to describe equipment owned by a telephone service provider that resided at customer premises, but it has evolved to include equipment owned by anyone. Telecom engineers often shorten the word premises to prem when speaking. Telecom Glossary DACCS DACCS (pronounced dacks) stands for Digital Access Cross-Connect System. You may also see this as DAX, or DACS®, which is a registered trademark of AT&T. A DACCS is a device that allows changes to the way voice channels are con- nected between trunks through the use of software. Figure 19-3 shows a logical representation of a DACCS in use. T1-A connects to the DACCS, and has 18 of its 24 channels in use. Those channels need to be routed to three different places. With the DACCS, we can link the first six channels (1-6) of T1-A to channels 1-6 on T1-B, the next six channels (7-12) of T1-A to channels 1-6 on T1-C, and the next six channels (13-18) of T1-A to channels 1-6 on T1-D. The channels do not have to be grouped, and may be mapped between links in any way, provided there are available channels on the links. T1 - B (24 Channels) T1 - A (24 Channels) T1 - C (24 Channels) T1 - D (24 Channels) Digital Access Cross Connect System (DACCS) Figure 19-3.