stream of information encoded as a CBR development within the ITU-T Study Group 13. stream. But in the real sense, voice is a combination of Let's discuss the ATM Trunking standard in brief-an talk spurts and silence. So bandwidth is wasted when important concept to understand in order to have a suc- transmitting the silence. These mechanisms also typi- cessful VoATM network. cally minimize the problems of cell construction delay by transmitting the voice as an uncompressed 64 kbps. a) Switched trunking Such approaches deny the network operator a chance to gain significant bandwidth from voice compression Switched trunking involves analysis of the signaling that technologies. To address these limitations, the ATM accompanies an incoming narrowband call and routing of Forum came up with the advanced mechanism for the its bearer information to an AAL2 channel within a VCC transport of voice as a VBR compressed stream. between IWFs. Once the narrowband call has ended, AAL2 is a new ATM Adaptation Layer, specified in subsequent calls occupying the same narrowband channel ITU-T Recommendation 1.363.2 (1997) with the specific (TDM timeslot) may be switched to different AAL2 mandate to provide efficient VoATM services. AAL2 channels and VCCs. In other words, there is no perma- supports, in addition to those of AAL1, the following nent relationship between a narrowband channel and an features: AAL2 channel. Efficient bandwidth usage through VBR traffic. b) Non-switched trunking ATM bandwidth reduction support for voice compres- sion, silence detection/suppression, idle voice chan- In non-switched trunking, the information stream of nel deletion. a narrowband channel is always carried on the same AAL2 channel within the same VCC. In other words, Multiple voice channels with varying bandwidth on there is a permanent correspondence between a narrow- a single ATM connection. band channel and the AAL2 channel and VCC desig- Thus AAL2 can enable voice applications by using nated for its support. Non-switched trunking involves 