Cisco NIM-2FXO
2-port Network Interface Module - FXO (Universal)
Product Highlights
Bridging legacy analog telephony with modern IP networks shouldn't require complex workarounds or expensive infrastructure overhauls. The Cisco NIM-2FXO is a 2-port Network Interface Module — FXO (Universal) designed to provide seamless PSTN connectivity for Cisco ISR 4000 Series routers.
This fourth-generation voice and fax network interface module features an integrated onboard DSP, eliminating the need for a dedicated packet voice DSP module (PVDM) on the router motherboard. Each of the two FXO ports connects to a standard analog PSTN line via RJ-11, enabling your Cisco ISR to make and receive calls over the public switched telephone network. The NIM-2FXO supports key voice protocols including SCCP, SIP, MGCP, and H.323, along with Cisco Unified Communications Manager Express (CME) for flexible unified communications deployments.
With support for online insertion and removal (OIR), the NIM-2FXO can be installed or replaced in a live router chassis without a full power-down cycle — a critical advantage for production environments where uptime matters. The module supports loop-start and ground-start signaling, echo cancellation up to 128 ms, VAD, CNG, T.38 fax relay, and modem passthrough. Whether you're providing PSTN failover for a VoIP deployment, connecting legacy analog lines at a branch office, or integrating fax services into your IP network, the Cisco NIM-2FXO delivers reliable, carrier-grade analog voice connectivity in a compact single-wide NIM form factor.
Features & Benefits
Integrated Onboard DSP
The NIM-2FXO includes a dedicated digital signal processor directly on the module, handling TDM analog voice services without consuming a PVDM slot on the host router. This simplifies deployment, reduces component costs, and frees up router resources for other services.
Hot-Swappable Design (OIR)
Online insertion and removal support means you can add, replace, or upgrade the NIM-2FXO in a live Cisco ISR 4000 chassis without powering down the router. This dramatically reduces planned maintenance windows and keeps your network available.
Flexible Voice Protocol Support
Compatible with SCCP, SIP, MGCP, and H.323, the NIM-2FXO integrates into virtually any Cisco Unified Communications environment. It also supports Cisco Unified CME and MGCP gateway configurations, giving you the flexibility to match your existing UC architecture.
High-Quality Voice & Fax
With 128 ms echo cancellation, voice activity detection (VAD), comfort noise generation (CNG), and T.38 fax relay, the NIM-2FXO ensures crystal-clear voice calls and reliable fax transmissions over IP. Codec support includes G.711, G.729a, and G.726.
PSTN Failover & Survivability
Deploy the NIM-2FXO as a secondary voice gateway to provide automatic PSTN failover when your primary VoIP WAN link degrades or fails. This ensures uninterrupted inbound and outbound calling for business-critical voice services at branch offices.
Deployment Scenarios
Branch Office PSTN Failover
In branch deployments where VoIP is the primary voice service, the NIM-2FXO provides automatic PSTN failover via two analog lines. If the WAN link goes down, calls seamlessly route over the PSTN, ensuring business continuity and uninterrupted customer communications.
Legacy Analog Line Integration
Small and medium businesses transitioning from traditional PBX systems can use the NIM-2FXO to connect existing PSTN lines to a Cisco ISR 4000 router. This enables a phased migration to IP telephony while preserving existing analog line investments.
Fax-over-IP Deployment
Organizations that still rely on fax communications can leverage the NIM-2FXO's T.38 fax relay capability to integrate analog fax lines into their IP network. This eliminates the need for standalone fax infrastructure while maintaining reliable fax delivery.
Retail & Distributed Enterprise Voice
Retail chains and distributed enterprises can deploy the NIM-2FXO at each site to aggregate local analog PSTN lines into the corporate VoIP network. This centralizes call management, simplifies telephony administration, and reduces per-site telecom costs.
General
Interfaces
Voice & DSP
Software
Physical
Compatibility
Compliance
Compatibility Notes
Supported Platforms:
- Cisco ISR 4000 Series routers (ISR 4321, 4331, 4351, 4431, 4451-X) — requires an available NIM slot
Minimum Software:
- Cisco IOS XE 3.13.4, XE 3.14.3, XE 3.15.1, XE 3.16 and above
Not Supported:
- Cisco 2900 and 3900 Series ISRs (these platforms do not support NIM-format modules)
Connector Type:
- RJ-11 (standard analog telephone cable per FXO port)
Note: No separate PVDM module is required — the NIM-2FXO has an integrated onboard DSP.
Downloads & Resources
Frequently Asked Questions
| Part Number | Product | Key Difference |
|---|---|---|
| NIM-4FXO | Cisco 4-Port FXO NIM | Doubles FXO port density to 4 ports for sites requiring more simultaneous PSTN lines |
| NIM-2FXS | Cisco 2-Port FXS NIM | Provides FXS ports to connect analog phones/fax machines directly, rather than PSTN trunk lines |
| NIM-2FXS/4FXO | Cisco Combo 2-Port FXS / 4-Port FXO NIM | Combines 2 FXS and 4 FXO ports in a single module for sites needing both analog endpoints and PSTN trunks |
| VIC2-2FXO | Cisco 2-Port FXO VIC2 (ISR G2) | Previous-generation voice interface card for ISR G2 routers — NIM-2FXO is the ISR 4000 successor with onboard DSP |
