If your network is among them, you'll need to decide what to do with frame relay and choose a concentrator that supports your decision. If you'll be running voice on your ATM backbone, the first thing to look for in a concentrator is the voice-interface modules. Digitized voice can be compressed using various methods. There are several standards for voice compression, and all are subjective. If your network is carrying interoffice voice traffic where quality is less of a concern than bandwidth, high compression can be used.
Intermediate quality is also available.
If you decide against compression, your concentrator should support circuit emulation. This lets you plug channelized T1 services directly into the switch. This one channel may also contain the signaling for other PRIs, thereby letting them use all 24 channels for user data. Each channel contains only 56 KB of user data space and 8 KB of signaling. More power to you if you don't need any management for your new concentrator, but for those products lacking a cybernetic intelligent controller and direct ESP transmission link to your IT staff, it might be worth considering.