Nortel NT8P29BA (telecommunications transmission and networking portfolio) Telecom System Card / Module

The Nortel NT8P29BA is an 8-port X.21 interface module for the DPN-100 packet-switching platform, providing eight X.21 wide-area serial connections from a single Processor Interface (PI) card position in the DPN-100 switching shelf. X.21 is the ITU-T standard synchronous serial interface widely used for leased-line and X.25 packet-network connections in this era, and this module let a DPN-100 node terminate multiple X.21 circuits (typically leased lines to remote sites or other network nodes) through one card slot rather than needing a separate interface per line. It belongs to the same family of DPN-100 Processor Interface cards as the V.24 and V.35 variants used on the same platform, each built for a different physical-layer standard while sharing the same processor-interface architecture. DPN-100 nodes remain in limited service, and X.25/leased-line WAN infrastructure built on this platform still exists in a small number of legacy telecoms and enterprise networks, where genuine interface modules of the correct standard are needed to keep specific circuits in service. Tech-Star (UK-based, shipped worldwide) supplies DPN-100 interface spares for legacy network maintenance.