ADTRAN's TSU Multiplexer Series redefined the T1 multiplexer marketplace in 1994. Today, this equipment is some of the most reliable and respected for aggregating multiple voice only or voice and data services onto T1 or FT1 bandwidths. The intelligent TSU and TDU devices offer either one (1XX series) or six (6XX series) expansion slots, with up to four interfaces per slot. More than thirty plug-in and plug-on modules are available to support analog voice, Nx56/64 data, subrate data, disaster recovery, and other applications. The "e" series devices additionally include SNMP management via a SLIP or 10BaseT port, an enhanced terminal screen.