Cisco NM-1HSSI High Speed Serial Interface HSSI Network Module Router Card

Cisco NM-1HSSI High Speed Serial Interface HSSI Network Module Router Card

The Cisco NM-1HSSI is a single-port High Speed Serial Interface (HSSI) network module designed for Cisco modular routers. It provides one HSSI WAN port capable of connecting to high-speed serial WAN services at rates up to 52 Mbps, making it suitable for Frame Relay, ATM, SMDS, HDLC, and PPP WAN deployments.

Specifications & What's Included

• Model: Cisco NM-1HSSI
• Type: High Speed Serial Interface (HSSI) Network Module
• Number of HSSI Ports: 1 (HSSI 0)
• HSSI Connector: DB-50 (50-pin HSSI standard)
• Maximum Data Rate: Up to 52 Mbps
• Router Backplane Connector: 68-pin NM slot edge connector (visible on PCB underside)
• Front Faceplate: LED status indicators — LBC, RC, RD, TC, TD
• Form Factor: Network Module (NM) for Cisco modular router NM slot
• Compatible Platforms: Cisco 2600 Series, 3600 Series, 3700 Series routers
• Protocol Support: Frame Relay, ATM, SMDS, HDLC, PPP
• PCB: Green multi-layer board with two main controller ICs visible

Applications

The NM-1HSSI was designed for Cisco modular routers that use the NM (Network Module) slot architecture, including the 2600, 3600, and 3700 series platforms — a family of enterprise branch-office and WAN aggregation routers that were widely deployed in the late 1990s and 2000s. HSSI (High Speed Serial Interface) is a point-to-point serial WAN standard developed in the early 1990s to bridge the gap between slower V.35/RS-449 serial interfaces and full LAN speeds, operating at up to 52 Mbps. The NM-1HSSI allowed these routers to connect directly to CSU/DSU equipment supporting high-speed leased-line, Frame Relay, and ATM services without an external serial adapter. HSSI connections were common in environments requiring dedicated high-bandwidth WAN links — data centers, ISP aggregation points, and large enterprise campus backbones of that era. While newer WAN technologies (MPLS, Metro Ethernet, broadband) have largely replaced HSSI in greenfield deployments, this module remains in demand for maintaining and extending legacy Cisco router installations still in service.