Cisco NM-1CT1-CSU
1-Port Channelized T1/ISDN-PRI with CSU Network Module
Product Highlights
Maintaining reliable T1/ISDN PRI WAN links shouldn't require a rack full of external equipment. The Cisco NM-1CT1-CSU eliminates the need for a standalone Channel Service Unit by integrating CSU functionality directly into a single-slot network module, simplifying your deployment and reducing points of failure.
This 1-port channelized T1/ISDN-PRI network module receives and transmits data bidirectionally at the standard T1 rate of 1.544 Mbps, supporting up to 24 virtual channels per port. Whether you're delivering ISDN PRI voice trunks to a PBX, building a channelized data WAN link, or aggregating dial-in access, the NM-1CT1-CSU provides the interface you need in a compact, router-integrated form factor.
Designed for Cisco 2600, 3600, and 3700 series access routers, the module connects directly to your T1 provider's RJ-48C demarc point using a standard straight-through cable — no external CSU, no extra power supply, no additional rack space. Configuration is handled entirely through Cisco IOS CLI, giving network engineers a familiar, scriptable management interface. For organizations maintaining legacy T1 infrastructure or supporting ISDN PRI voice services, the NM-1CT1-CSU remains a proven, cost-effective solution.
Features & Benefits
Integrated Channel Service Unit (CSU)
The built-in CSU allows the module to connect directly to the T1 network via a standard RJ-48C jack, eliminating the cost and complexity of an external CSU appliance. This reduces cabling, saves rack space, and removes a potential point of failure from your WAN path.
Channelized T1 with Up to 24 Time Slots
Each T1 port supports up to 24 DS0 (64 Kbps) virtual channels that can be individually assigned to voice, data, or signaling. This granular bandwidth allocation lets you run mixed voice/data workloads over a single physical T1 circuit, maximizing your service provider investment.
ISDN PRI Support
Full ISDN Primary Rate Interface support enables 23B+D channel configurations for voice trunking, dial-in access, and ISDN backup scenarios. The module integrates seamlessly with Cisco IOS dial and voice gateway features for PBX interconnection and call routing.
Broad Cisco Router Compatibility
The NM-1CT1-CSU is supported across the Cisco 2600, 3600, and 3700 series router families, giving you flexibility to deploy T1/PRI connectivity in branch offices, remote sites, and campus aggregation points without changing platforms.
Cisco IOS CLI Management
All configuration — from T1 framing and line coding to ISDN switch type and channel group assignments — is performed through the standard Cisco IOS command-line interface. This means no separate management tools, consistent automation via scripts, and a familiar workflow for your network team.
Deployment Scenarios
Branch Office T1 WAN Connectivity
Deploy the NM-1CT1-CSU in a Cisco 2600 or 3700 series router at a branch office to provide a dedicated T1 WAN uplink to the corporate network. The integrated CSU simplifies installation at remote sites where minimizing equipment and truck rolls is critical.
ISDN PRI Voice Trunking
Use the module to deliver a 23B+D ISDN PRI trunk between a Cisco voice gateway and a legacy PBX or the PSTN. This enables inbound/outbound call routing, DID services, and ISDN-based call control without external T1 termination hardware.
Dial-In Access Aggregation
Pair the NM-1CT1-CSU with digital modem network modules in a Cisco 3600 series router to build a dial-in access server. The channelized T1 PRI interface receives incoming ISDN calls and routes them to internal modem resources for remote user authentication and connectivity.
ISDN Backup / Redundant WAN Link
Configure the T1/PRI port as a backup WAN interface that activates automatically when a primary link fails. Cisco IOS dial backup and floating static route features make failover seamless, keeping critical sites connected during outages.
General
Interfaces
Performance
Compatibility
Environmental
Compatibility Notes
Compatible Router Platforms
- Cisco 2600 Series (2610, 2611, 2620, 2621, 2650, 2651, 2610XM, 2611XM, 2620XM, 2621XM, 2650XM, 2651XM)
- Cisco 3600 Series (3620, 3640, 3660)
- Cisco 3700 Series (3725, 3745)
Minimum Cisco IOS Release
- 12.0(7)XK or 12.1(1)T (or later)
Cabling
- Use a straight-through RJ-48C to RJ-48C cable to connect the module directly to the T1 provider demarc.
Digital Modem Compatibility
- When used with digital modem network modules, the NM-1CT1-CSU must be revision level -03 or higher.
Downloads & Resources
Frequently Asked Questions
| Part Number | Product | Key Difference |
|---|---|---|
| NM-1CT1 | 1-Port Channelized T1/ISDN-PRI (without CSU) | Requires an external CSU; uses a DB-15 connector instead of RJ-48C — lower module cost but additional external hardware needed. |
| NM-2CT1-CSU | 2-Port Channelized T1/ISDN-PRI with CSU | Doubles capacity to two T1/PRI ports with integrated CSU — ideal when you need 48 channels or dual-link redundancy in a single module slot. |
| NM-2CT1 | 2-Port Channelized T1/ISDN-PRI (without CSU) | Two T1/PRI ports without built-in CSU; requires external CSU for each port but offers dual-port density. |
| NM-1CE1B | 1-Port Channelized E1/ISDN-PRI Balanced | E1 variant operating at 2.048 Mbps with up to 30 channels — designed for international deployments using E1 circuits instead of T1. |