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Max Analog Phones on a single FXS / ATA / VG port

Hi all,

I'm now working on the planning of an IP Telephony solution, now the customer is asking me about the max ammount of analog phones i can conect to a single physical line of a FXS port ot ATA or VG, since the actual solution allows them to connect several phones to the same physical telephone line, is there a limit of analog phones to be connected to a single physical line of an fxs port?

we are building the solution with VIC2-2FXS cards


Everyone's tags (2)

Re: Max Analog Phones on a single FXS / ATA / VG port

The supported solution is one analog phone to one fxs port. It is my assumption that you could split it at the ATA via some kind of pigtail, but you would still only be able to make one call to that ATA/"phone line", simply because it is ip based, not frequency based. The ATA would not know how to differentiate between the two simultaneous calls. You probably could get by with having multiple analog phones attached to the ATA but only one would be usable. Kind of like an archaic shared line.



Re: Max Analog Phones on a single FXS / ATA / VG port

Hi Bill,

Thanks for you answer, i agree it is not a regular type of installation, but is the customer requirement, do you have any doc stating the reason why it is not supported/recommended to share the physical line of the FXS port? customer want to know what is the risk of doing so and the technical reason about it. also i will like to know what is the maximum ammount of devices suported per line.


Cisco Employee

Re: Max Analog Phones on a single FXS / ATA / VG port

Dear Sir;

Our SPA ATAs (and typically majority of ATAs) are REN 3. REN is the Ring Equivalent Number which equates to max current the port can source. How many phones can be attaches? Well, it depends on the type of phones and countries, but most phones are on 0.6 and 1 REN. That's you can connect 3-5 standard phones.

A safe number is 3, if phones are standard.