Cisco NM-HDA-4FXS
High density analog voice/fax network module with 4 FXS
Product Highlights
Integrating legacy analog telephony devices into a modern IP network shouldn't require a forklift upgrade. The Cisco NM-HDA-4FXS is a high-density analog voice and fax network module that provides four Foreign Exchange Station (FXS) ports, enabling you to connect analog telephones, fax machines, and modems directly to a Cisco router.
Designed as a plug-in network module, the NM-HDA-4FXS features two built-in C5421 DSPs that support up to 8 high-complexity or 16 medium-complexity voice channels. It handles voice calls, fax relay, fax pass-through, and modem pass-through — all from a single NM slot. With support for both loop-start and ground-start signaling, DTMF detection, voice compression and decompression, and caller ID, this module delivers the full range of analog telephony features IT teams need.
The NM-HDA-4FXS is compatible with a wide range of Cisco Integrated Services Routers, including the 2600, 2600XM, 2691, 3640, 3660, 3725, 3745, 2800, and 3800 series. Whether you're maintaining branch-office voice infrastructure, bridging analog endpoints into a VoIP deployment, or supporting fax-over-IP workflows, this module provides a cost-effective, space-efficient solution that leverages your existing Cisco router investment.
Features & Benefits
High-Density Analog Voice Integration
The NM-HDA-4FXS delivers four FXS ports via standard RJ-11 connectors, allowing direct connection of analog phones, fax machines, and modems. The high-density analog (NM-HDA) module family supports up to 16 analog ports per module — four times the capacity of the low-density NM-2V modules — maximizing port density per NM slot.
On-Board DSP Processing
Two built-in Cisco C5421 DSPs provide local voice processing without consuming external PVDM resources for the base port count. The module supports up to 8 high-complexity or 16 medium-complexity voice channels, enabling flexible codec selection based on bandwidth and quality requirements.
Comprehensive Telephony Features
Beyond basic voice, the NM-HDA-4FXS supports fax relay, fax pass-through, and modem pass-through — critical for organizations that still rely on analog fax workflows. DTMF detection, voice compression/decompression, caller ID support, and battery feed are all built in, ensuring full-featured analog telephony integration.
Flexible Signaling Support
Both loop-start and ground-start signaling are supported on the FXS ports, providing compatibility with a wide range of analog endpoint equipment. This flexibility simplifies deployment in environments with mixed or legacy telephony gear.
Broad Cisco Router Compatibility
The NM-HDA-4FXS installs into any standard NM slot on compatible Cisco routers, including the 2600, 2600XM, 2691, 3640, 3660, 3725, 3745, 2800, and 3800 series. This broad compatibility protects your investment and simplifies sparing across multi-site deployments.
Deployment Scenarios
Branch Office Voice Gateway
Deploy the NM-HDA-4FXS in a branch-office Cisco router to connect analog desk phones and fax machines to a centralized VoIP system. The four FXS ports provide enough capacity for small offices while the on-board DSPs handle voice processing locally, reducing WAN bandwidth consumption.
Analog-to-VoIP Migration
Organizations transitioning from legacy PBX systems to IP telephony can use the NM-HDA-4FXS to bridge existing analog endpoints into the new VoIP infrastructure. This avoids the cost of replacing every analog device on day one and allows a phased migration.
Fax-over-IP Deployment
For businesses that still depend on fax communication — such as healthcare, legal, and financial services — the NM-HDA-4FXS provides fax relay and fax pass-through capabilities. Connect analog fax machines directly to the router and route fax traffic over the IP network reliably.
Survivable Remote Site Telephony (SRST)
Pair the NM-HDA-4FXS with Cisco SRST on a branch router to ensure analog phones remain operational even when the WAN link to the central call-control server is down. This provides business-continuity for critical voice services at remote locations.
General
Interfaces
Performance
Features
Environmental
Compatibility
Compatibility Notes
Compatible Cisco Router Platforms
- Cisco 2600 Series: 2610, 2611, 2612, 2613, 2620, 2621, 2650, 2651 (and XM variants)
- Cisco 2691
- Cisco 2800 Series: 2821, 2851
- Cisco 3600 Series: 3620, 3640, 3660, 3661, 3662
- Cisco 3700 Series: 3725, 3745
- Cisco 3800 Series: 3825, 3845
Software Requirements
- Requires Cisco IOS with voice feature set (e.g., IP Voice, SP Services, or Advanced IP Services)
- Configuration support documented for Cisco IOS Release 12.2(2)XT and 12.2(8)T and later
Notes
- This is the base NM-HDA module with 4 FXS ports. Additional analog ports can be added via expansion modules (e.g., EM-HDA-4FXS, EM-HDA-8FXS) installed into the NM-HDA carrier.
- The module occupies one full NM slot in the router chassis.
Downloads & Resources
Frequently Asked Questions
| Part Number | Product | Key Difference |
|---|---|---|
| NM-HDA-4FXO | 4-Port FXO High-Density Analog Module | Provides 4 FXO ports (connects to PSTN/PBX trunk lines) instead of FXS ports (connects to analog endpoints) |
| EM-HDA-4FXS | 4-Port FXS Expansion Module for NM-HDA | Expansion daughter card that adds 4 FXS ports to an existing NM-HDA base module — requires an NM-HDA carrier |
| NM-HDA-8FXS | 8-Port FXS High-Density Analog Module | Doubles the FXS port count to 8 in a single NM slot for higher-density analog voice deployments |
| VIC-4FXS/DID | 4-Port FXS/DID Voice Interface Card | VIC form factor card providing 4 FXS/DID ports — installs into a VIC slot on an NM or router motherboard |
