 be aggregated into part of a larger SONET system. Channel bank A channel bank is a device that separates a T1 into 24 individual analog phone lines, and vice versa. Today, private branch exchanges (PBXs) usually take care of partitioning T1s into analog lines, thereby eliminating the need for a channel bank. Chapter 20: Telecom Nomenclature 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 signaling 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 include a PBX, phones, routers, and even cable modems. Traditionally, the term was used to describe equipment owned by a tel- ephone 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. 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 connected between trunks, through the use of software. Figure 20-3 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