Cisco High Density Voice Fax Network Modules

Understanding High-Density Analog Voice/Fax Network Modules (NM-HDA)

Document ID: 20365

Updated: Feb 16, 2006



The analog voice/fax network modules provide standard analog interface to the telephony equipment and Public Switched Telephone Network (PSTN). The high-density analog voice/fax network modules (NM-HDA) serve up to 16 analog ports, or four times the number of ports that the low-density analog voice/fax network modules (NM-2V) support. The ports can be in these combinations:

  • 4 Foreign Exchange Station (FXS) ports

  • 12 FXS ports

  • 4 FXS and 4 Foreign Exchange Office (FXO) ports

  • 4 FXS and 8 FXO ports

  • 12 FXS and 4 FXO ports

The base card supports 4 FXS ports.

  • The addition of an 8-port FXS expansion module (EM) can increase the capacity to 12 FXS ports.

  • The addition of two 4-port FXO EMs can increase the capacity to 8 FXO ports along with 4 FXS ports.

  • The addition of one each of the FXS and FXO EMs can increase the capacity to 12 FXS ports and 4 FXO ports.

This diagram shows the NM-HDA:




There are no specific requirements for this document.

Components Used

This document is not restricted to specific software and hardware versions.


Refer to Cisco Technical Tips Conventions for more information on document conventions.

Product Numbers

Product Description Notes
NM-HDA-4FXS NM-HDA with 4 FXS ports Base module
EM-HDA-8FXS 8-port voice/fax EM—FXS Expansion module
EM-HDA-4FXO 4-port voice/fax EM—FXO Expansion module
DSP-HDA-16 16-channel DSP1 module for NM-HDA DSP module (required for some configurations)

1 DSP = Digital Signal Processor

Note: You cannot use two EM-HDA-8FXS modules on an NM-HDA base board. All other combinations are valid.


  • Voice, fax relay, fax pass-through, and modem pass-through are supported.

  • Ground-start and loop-start are supported on both FXS and FXO ports.

  • DSPs are on the base module board and the DSP EM (DSP-HDA-16).

  • Uses a standard telephone company (telco) RJ-21 amphenol connector, which is not provided with the network module. For pinout and additional information, refer to the document Connecting High-Density Analog Telephony Network Modules.

  • Some recommended RJ-21 cables are:

    • 253PP10GYADI male-to-male cable and 253PC10GYADI male-to-female cable from Gray Bar.

    • AT125-SM patch panel, which supports both male and female connection, from Gray Bar.

  • Port numbers are statically allocated to each slot in the NM-HDA and do not change based on the module that is plugged into that slot.

    • Base module (FXS): x/0/0-x/0/3

    • EM in slot 0 (FXS): x/0/4-x/0/11

    • EM in slot 0 (FXO): x/0/4-x/0/7

    • EM in slot 1 ( FXS): x/0/14-x/0/21

    • EM in slot 1 (FXO): x/0/14-x/0/17

  • FXS and FXO battery polarity reversal disconnect are supported.

  • FXO Answer and Disconnect Supervision are supported.

  • The FXO Power Failure feature is a hardware feature that is built into the FXO cards. The feature allows connectivity to an analog phone that is patched into the right pair of wires to be activated by a relay if power to the router that contains the NM-HDA fails.

  • These are supported:

    • VoIP H.323, VoIP session initiation protocol (SIP), and VoIP Media Gateway Control Protocol (MGCP) with Call Agent

    • Voice over Frame Relay (VoFR)

    • Voice over ATM (VoATM)

    • VoATM adaptation layer 5 (VoAAL5)

    • Trunked ATM adaptation layer 2 (AAL2)

  • VoIP H.323 and MGCP with Cisco CallManager are supported.

  • There is hookflash support. For the configuration, refer to the NM-HDA Timing Commands section of the document Cisco High-Density Analog Voice and Fax Network Module.

  • Caller ID is supported on FXS and FXO ports.

For software and memory requirements, specifications, and homologation of NM-HDA, refer to the document IP Communications High Density Analog Voice/Fax Network Modules.

For information on how to add port EMs, DSP EMs, and network module LEDs, refer to the document Connecting High-Density Analog Telephony Network Modules.


For the configuration of voice features in Cisco IOS® Software, refer to the document Voice over IP for the Cisco 3600 Series.

Note: In Cisco IOS Software, issue the voice-port slot/VIC-slot/unit global configuration command in order to configure the voice port parameters. The middle digit of the port number for the NM-HDA is always "0".

Platform Support

Cisco IOS Software Support 1 2600 2600XM 3640, 3660 2691, 3725, 3745
Maximum Number of Modules 1 1 3640 - 3 3660 - 6 2691 - 1 3725 - 2 3745 - 4
NM-HDA Cisco IOS Software Releases 12.2(2)XT, 12.2(8)T, 12.2(11)YT, 12.3(1) Cisco IOS Software Releases 12.2(8)T1, 12.2(11)T, 12.2(11)YT, 12.2(15)ZJ, 12.3(1), 12.3(2)T Cisco IOS Software Releases 12.2(2)XT, 12.2(8)T, 12.2(11)YT, 12.2(15)ZJ, 12.3(1), 12.3(2)T Cisco IOS Software Releases 12.2(8)T1, 12.2(11)YT, 12.2(15)ZJ, 12.3(1), 12.3(2)T, 12.3(4)XD

1 The module requires the Cisco IOS Software "Plus" feature set. The NM-HDA module is not supported on:

  • Cisco 1700 series routers

  • Cisco 3620 router

  • Catalyst 4500/4000 series switches

  • Catalyst 6500/6000 series switches

Voice is not supported on the Cisco 3631 router.

Note:  This module is not supported in the Cisco IOS Software "Enterprise Basic" (-j1s3) feature set. It may not be supported in other basic feature sets for these routers:

  • Cisco 261x (non-XM model)

  • Cisco 262x (non-XM model)

  • Cisco 3620 routers

For more information, refer to Field Notice: Cisco 2600 and 3600 IOS Software Feature Changes for 12.2(8)T and Table 3 of Cisco 2600/3620 Associated Feature Image and Memory Updates.

Note: The Cisco IOS Software releases that this document names are typically the minimum versions that are required in order to support the platform, module, or feature in question. For a complete list of Cisco IOS Software releases in which a feature, module, interface card, or chassis is supported, refer to the Software Advisor (registered customers only) tool.

Related Information

Updated: Feb 16, 2006
Document ID: 20365