one 64-Kbps D (Data) channel (23 B and D). Diff-Serv Differentiated Services The Diff-Serv model divides traffic into a small number of classes to provide quality of service (QoS). PSTN Public Switched Telephone Network The worldwide voice telephone network. DNIS Dialed Number Identification Service A telephone function that sends the dialed telephone number to the answering service. SIP Session Initiation Protocol A protocol that provides telephony services similar to H.323, but
