Cisco FXS/FXO VOIP Gateways

Contents • Introduction (Right) • IAD2400 FXS gateways  • 2600/3600/3700 FXS/FXO routers • Expansion Modules (WIC-Type, AIM, and NM-Type) • FXS/FXO router pricelist  • Cisco documentation for 2600/3600/3700 FXS/FXO • Cisco documentation for IAD2400 FXS/FXO

FXS/FXO VOIP routers differ from POTs lines analog dialup gateways, which function like dialup gateways except that instead of using PRI lines (bundles of 24 or 30 digital phone lines in a single cable), POTs dialup gateways use individual, ordinary phone lines. Click here for details on POTs line analog dialup gateways.

One important distinction between FXS/FXO routers and other VOIP gateways is that FXS/FXO routers use ordinary phone lines and connectors, rather than digitized PRIs, to create the VOIP network. FXS/FXO configurations are particularly suited to settings only requiring a very small number of VOIP phone connections - typically no more than 8, or 16 at the most. 

Cisco's the IAD2400 series (Integrated Access Device) contains only FXS ports. It is a specialized router designed only for connecting a small office phone POTs type systems to the internet, or to set up a VOIP network where only ordinary POTS phone lines are available.  On the IAD2400 shown here, the FXS interface is at the far left side of the router. A special cable attaches to the IAD at that point which breaks out into individual jacks for connecting phone, lines, or other devices. Common configurations are 8FXS and 16FXS, and model lines include IAD2421, IAD2431, and IAD2432. Click here for Cisco's IAD2400 documentation.

It is also common and possible to use any 2600, 3600, or 3700 modular router as an FXO/FXO VOIP gateway. For example, assume you have a 2621 modular router, and want a VOIP router with 2 FXS and 2 FXO ports. The 2621 router has a base configuration that includes 1 NM port, 2 WIC ports, and 2 built-in 10/100 ethernet ports. You would need to install an NM-2V card with 1 VIC-2FXS and 1 VIC-2FXS cards in the NM port. The 2 FXO ports would be cabled into the phone jacks coming out of the wall (or just 1 if you only have one phone line) giving you 2 phone system lines to receive and make phone calls into the public phone network. Up to 2 phones could then be attached to the 2 FXS ports, and other office telephone equipment like fax machines could be daisy-chained to them as well. An ethernet port would be used to connect the router to the internet. Based on the software configuration you create, this gateway is able to send and receive phone calls both over the public phone system and the internet. Pictured here is a 2611XM with NM-2V in which 2 VIC-2FXS are installed (4 FXS total). Any combination of 2FXS and 2FXO are possible.

Introduction:  FXO and FXO based gateways enable VOIP networks to be created using ordinary phone lines and phone equipment. FXS and FXO ports are regular phone-jack-type ports. An FXS port plugs into a regular telephone - just like a regular (nonIP) phone would plug into the wall. Like a normal phone line, an FXS port will ring the telephone, and your will hear a dialtone when you list to the receiver. FXO ports connect phone systems into other digital and network equipment, including your router. An ordinary telephone will not work if plugged into an FXO port, because it does not general ring current or dialtone. Small office networks are often connected using FXS/FXO equipment this way. A router is connected to the public telephone systems (PSTN) using one or more FXO ports. The same router is connected to office phone lines using FXS ports. The same router connects calls in and out over the internet (including to another office's router) through its ethernet port and internet connection.

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