Thursday, February 03, 2005

Does Your VoIP Have a Lifeline?

The whole idea behind VoIP is to avoid the PSTN or Public Switched Telephone Network as much as possible. The PSTN is like a toll road. Every time you use it you have to pay a toll. The Internet is more like a freeway as far as telephony goes. Once you pay for access there is no nickel and diming for each phone conversation. But, what happens when your VoIP network slows down like a congested highway or some accident stops traffic altogether. Now what do you do?

The easy answer is to get back on that PSTN tollway until your VoIP is available again. That option is now being included in some of the newer ATAs, Analog Telephone Adaptors, used for single and dual line VoIP or hosted PBX solutions. The extra port is called a "PSTN Lifeline" or sometimes an FXO Interface. FXO stands for Foreign Exchange Office, which is a connection to a normal phone company line.

With ATAs that include a PSTN Lifeline, you plug your phone and broadband connection into the adaptor and connect the lifeline port to a regular analog phone line. It's a standard RJ11 telephone jack like you'd find on the back of a telephone. The magic is that when your VoIP service is down because of a broadband failure or a problem with your VoIP provider's proxy server or softswitch, the ATA will automatically switch your calls through to the public telephone network locally. Some ATAs automatically route 911 emergency calls through the PSTN lifeline, since not all VoIP services offer E911 service.

Examples of VoIP Analog Telephone Adaptors that include a PSTN Lifeline or the ZyXEL Prestige 2002L and the Grandstream HandyTone 486. It's likely that you'll be seeing this feature on more ATA products in the future.

At the Enterprise level, FXO ports are commonly included in routers being used for VoIP traffic. They are used as lifelines but also to give phones in one area the ability to make "local" phone calls in another. The calls travel from office to office over the corporate WAN and then are terminated to an FXO port at the destination location. This avoids paying toll charges when you have a perfectly good T1 or other high speed digital line running between locations already.

You can read more about how ATAs work in my article "Turning Analog Phones Into VoIP Phones." You might also be interested in reading "Hosted PBX Lets Small Businesses Act Big." Visit Enterprise VoIP for more VoIP information and solutions.

Click to check pricing and features or get support from a Telarus product specialist.


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