Cisco ISR 4000 Router Modules & Cards

Cisco ISR 4000 Voice NIM Modules and Cards

Cisco ISR 4000 voice NIM modules are used to add analog voice interfaces to supported Cisco 4000 Series Integrated Services Routers. These modules are commonly used for branch voice gateways, analog phones, fax machines, PBX connections, PSTN backup lines, DID services, and small office voice deployments.

This category focuses on Cisco ISR 4000 analog voice NIM options, including FXO, FXS, FXS/DID, and combo FXS + FXO modules. Before choosing a module, confirm the router model, available NIM slot, IOS XE version, voice license package, number of analog ports, PSTN or endpoint connection type, and whether the design requires FXO, FXS, DID, or a mixed voice interface.

Quick Selection Guide

How to Choose ISR 4000 Voice NIM Modules

Choose FXO NIMs for PSTN, PBX, and Carrier Analog Lines

FXO ports are used when the router needs to connect to external analog phone lines, PBX trunks, key systems, or PSTN services. Choose a 2-port FXO module for smaller sites and a 4-port FXO module when the branch needs more analog trunk capacity. FXO is the correct direction when the router receives analog service from the outside line.

Choose FXS NIMs for Analog Phones and Fax Machines

FXS ports are used when the router needs to connect directly to analog endpoints such as phones, fax machines, modems, or other analog voice devices. Choose a 2-port FXS module for small endpoint counts and a 4-port FXS module when the branch needs more analog device ports. FXS is the correct direction when the router provides the analog phone port to the endpoint.

Choose Combo FXS + FXO NIMs for Mixed Branch Voice

For branch offices that need both analog endpoints and analog PSTN lines in one module, choose a combo FXS + FXO voice NIM. This is useful when a site needs to connect local phones or fax devices while also keeping analog PSTN lines for backup, survivability, or local calling.

Understand P-Version FXS Modules

P-version FXS modules are newer hardware versions created because of component changes in the manufacturing process. They serve the same functional role as the corresponding non-P FXS modules. Use the P-version when it is the available replacement SKU or when the router software release and platform support match the deployment requirement.

FXO vs FXS: Which One Do You Need?

Voice Module Selection Notes

• Choose FXO when the router connects to an outside analog phone line or PBX trunk.
• Choose FXS when the router connects directly to an analog phone, fax machine, or endpoint.
• Choose a combo FXS + FXO module when the branch needs both endpoint ports and PSTN line ports.
• Confirm the Cisco ISR 4000 router model and available NIM slot before ordering.
• Confirm IOS XE release support and required voice feature package before deployment.
• Do not confuse analog voice NIMs with PVDM modules. These analog voice NIMs include onboard DSP for analog voice services.
• For conferencing, transcoding, or higher-density DSP resources, a separate PVDM design may still be required depending on the voice architecture.

Common Buying Mistakes

• Buying FXS when the project needs FXO for PSTN or PBX lines.
• Buying FXO when the project needs FXS ports for analog phones or fax machines.
• Assuming a PVDM module can replace an analog FXS or FXO interface card.
• Forgetting to check whether the router has an available NIM slot.
• Ignoring IOS XE and voice license requirements for Cisco ISR 4000 voice deployments.
• Choosing too few ports for future analog phone, fax, or PSTN expansion.
• Mixing ISR 4000 voice NIMs with older ISR G2 VIC/VIC2 modules without checking compatibility.

Before You Order

To choose the correct ISR 4000 voice NIM, prepare the router model, IOS XE version, available NIM slot, number of required analog ports, voice license status, PSTN or PBX connection type, endpoint count, fax requirement, and whether the deployment needs FXO, FXS, DID, or a mixed FXS + FXO configuration.