The ADTRAN ISDN Service Unit (ISU) 128 connects data terminal equipment (DTE) to the ISDN network. The ISU 128 is a full-featured single port terminal adapter that allows cost-effective high-speed data transmission at rates up to 128 kbps. Available in standalone or rackmount configurations, the ISU 128 is ideal for LAN/WAN connectivity or disaster recovery. ISDN service is delivered from the network by a single 2-wire U-interface connected directly to the ISU 128. The ISU 128 responds to loopback commands from the telephone company central office to make testing easy. The ISU 128 allows the user to migrate existing networks to an ISDN environment. The ISU 128 interoperates with V.34 modems (optional) and Switched 56 DSUs, as well as various ISDN terminal adapters, inverse multiplexers and multilink PPP-compatible routers. The ISU 128 provides connectivity to EIA-530, EIA-232 or V.35 DTE devices. The ISU 128 performs at synchronous data rates of 2400 bps to 128 kbps and asynchronous rates of 300 bps to 115.2 kbps. At rates over 64 kbps, multilink PPP or the BONDING delay equalization protocol synchronizes data over the two 64 kbps B channels. The ISU 128 also supports dedicated leased 2B1Q services. This provides a dedicated point-to-point service with no dialing necessary. The front panel of the ISU 128 standalone consists of a two-line by 16-character display, seven LEDs, and a 16-button keypad. Configuration, testing and monitoring of the unit can be accomplished through the front panel, a VT 100 terminal connected to the maintenance port, or remotely over the ISDN line.