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.