Cisco VoIP Hardware and Software

Up to this point, we has been focused on the underlying technologies and concepts that are integral to VoIP. We will now turn our attention to Cisco-specific information. Cisco offers a variety of hardware and software solutions for implementing VoIP. Its routers and switches can be adapted to support voice communications, usually with the addition of voice modules and software in many cases.

Voice Modules and Cards

Routers and switches use voice modules to transform and transport voice traffic across the IP network. They use Voice Interface Cards (VICs) to provide connectivity to telephone equipment. Voice Network Modules (VNMs) and VICs are configured using Cisco IOS VoIP commands. Digital signal processors are used in various Cisco voice-enabled routers in order to convert analog voice signals to digital for transmission across an IP network and to convert back to analog once the packet has arrived at the destination router. DSPs can be found as modules inserted onto the motherboard, as on the 1700 series routers, or as slots built onto a VNM that is placed in the router.

Voice Network Modules

VNMs convert analog voice into a digital form for transmission over the IP network. At least one VNM is needed to enable the router to handle voice traffic. VNMs come in several different models for the 2600/3600 series routers. Figure 1 shows several models of VNMs available for the 26XX and 36XX routers.

Figure 1: Voice Network Modules

Only VICs are supported in the carriers with a V in the name. The NM-1V is a one-slot VNM. You can install one VIC in the NM-1V to gain up to two voice ports. The NM-1V/2V does not support WAN interface cards (WICs). The NM-2V is a two-slot version of the VNM. You can install up to two VICs in the NM-2V, providing up to four voice ports. The NM-HDV high-density VNM. This network module consists of five slots, one for the voice WIC (VWIC) and four for the packet voice DSP modules (PVDM). You can install one VWIC in the NM-HDV, providing up to two voice ports. The VNMs are the housings for the actual voice interface cards that provide the necessary functionality and connectivity to achieve voice communications.

Voice Interface Cards

Voice Interface Cards (VICs) are inserted in the VNM to provide the necessary interface and support for the desired type of voice configuration (FXS, FXO, or E&M). Figure 2 shows several VICs to give you an idea of what is available; this is not an exhaustive list, as Cisco continues to expand in this area.

Figure 2: Voice Interface Cards

One thing we would caution you about is that physically and outwardly, there is no difference between the FXS and FXO connectors; it can be easy to plug a telephone into what you think is an FXS port, but is actually an FXO port. Ensure that you are using the proper port type by checking the color and labels before attempting to connect.

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  VIC-2E/M The two-port E&M module VIC-2E/M connects an IP network directly to a PBX system. It can be configured for special settings associated with tie-line ports on most PBXs. E&M ports are color-coded brown.
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  VIC-2FXS The two-port FXS module VIC-2FXS connects to endpoint equipment such as a telephone, keypad, or fax. These ports provide ringing voltage, dial tone, and other endpoint specific functionality. FXS ports are color-coded gray.
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  VIC-2FXO The two-port FXO module VIC-2FXO connects to a PBX or PSTN. FXO ports are color-coded pink. Other types of FXO cards for use outside North America are capable of providing switching and signaling techniques used in other geographic regions such as VIC-2FXO-EU for use in Europe.
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  VWIC-2MFT-T-1 The two-port VWIC multiflex trunk interface card is a two-port card that can be used for voice, data, and integrated voice/data applications. The multiflex VWIC can support data-only applications as a WAN interface on the Cisco 1700, 2600, or 3600. It can also integrate voice and data with the Drop and Insert multiplexer functionality and/or configured to support packetized voice (VoIP) when in the digital T-1/E-1 network module.
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  Two-Port ISDN BRI Card Two two-port ISDN BRI VICs are available for the Cisco 1700, 2600, and Cisco 3600 series routers. These cards are available as ISDN BRI S/T or NT interfaces for terminating to an ISDN network.
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  Four-Port Analog DID/FXS VICs Two direct inward dial interface cards are available. One card is a two-port RJ-11 that supports DID only. These cards are used for providing DID service to extensions on a PBX so that users may transparently dial directly to extensions.