The TDU 120e (T1 Distribution Unit) is an intelligent, full-featured, NEBS compliant, T1 DSU/CSU in a 1U high 19-inch rack mount enclosure. Designed to interface customers data terminal equipment (DTE) to T1 or fractional T1 services, the TDU 120e is fully compatible with D4 or ESF framing formats with AMI or B8ZS coding. When in ESF framing mode, the unit satisfies ANSI T1.403 and AT&T 54016 modes for utilization of the facility data link (FDL). It uses option modules identical to those used with ADTRAN TSU units. The TDU 120e also provides complete monitoring and control of the T1 network with embedded simple network management protocol provided through both a SLIP and a 10BaseT ethernet interface.