This 4-port BRI voice and fax expansion module has ports are that are configurable for NT or TE mode. This module allows connection to an ISDN S/T network by replicating either the network side or the terminal side. In NT mode the ports replicate the PSTN interface to a PBX that is compatible with European Telecommunications Standards Institute (ETSI) NET3 and QSIG switch types. In TE mode the ports support the same ISDN protocols as other Cisco Systems® products to allow connection to ISDN S/T networks, or through an external NT1 to ISDN U-interfaces. This module provides four on-premises S/T BRI trunk connections to the ISDN PBX.