They are highly flexible network termination units that directly connect a DTE with serial and / or E1 interface to an ATM network through a ShDSL line. The 2-wire and 4-wire models respectively provide two different modes of operation, E1 Cell Bridging and Frame Relay to ATM interoperability features, connected to a DSLAM, terminating the ShDSL and many other xDSL links. It concentrates up to 128 virtual circuit (VCC) connections through a single or double high-speed link to the backbone ATM network, reaching up to 4608kbps (4-wire mode). The deployment of a low-cost, highly scalable network infrastructure replaces DCE transceivers, obsolete HDSLs, TDM cross-connections, and other leased line equipment.