in-house telephone switching system that interconnects telephone extensions to each other as well as to the outside telephone network. DID Direct Inward Dialing The ability to make a telephone call directly into an internal extension without having to go through the operator. PRI Primary Rate Interface An ISDN service that provides 23 64-Kbps B (Bearer) channels and one 64-Kbps D (Data) channel (23 B and D). Diff-Serv Differentiated Services The Diff-Serv
