There is often the need to pass non-ATM or legacy traffic over an ATM network, to also benefit from the QoS and management capabilities. Typical uses are E1 for inter-PBX traffic, E3 for high quality video such as broadcast TV, E2 and E3 for onward conversion to HSSI Interfaced Routers (using Metrodata FM 4850,4900,4950 or the new DC3445.)
A practical example is that of integrating Digital Circuit-switched PBX's e.g.. Meridian, IsDX, SDX, together with an IP routing, into a core ATM network together, for the quality guarantees and predictability.
This defers replacing the perfectly good Digital PBX's with VOIP products. Also avoids any risks of unpredictable degraded voice transmission.
ATM Circuit Emulation Datasheet