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SRP52x FXO Inbound calls

Thanks to this community, I've understand that the FXO line of an SRP52x is a "life line" only. This is OK for me, it's exactly what I'm lookin for:

I want to use a SIP number for outside calls and be able to make and receive calls even when power is off and/or internet/Sip provider are down.

The question arises on normal operation: I supposed that inbound calls, coming from FXO line, go in transparency: this doesn't seem the case, at least in my installation. If this behaviour is planned, this unit is unuseful by my point of view: how can people looking for me know what number to dial to call me? Obviously the life line number is different from the SIP one, and, even more obviously, some of my new correspondents have the second, the olders have the first: I think that's normal to pretend to be reached from both.

Thanks for any suggestions

Tiziano Martelli

David Carr
Frequent Contributor


Hello, the FXO line is more or less a fail safe and not dependent on the internet as you stated and the SIP is dependent on the internet to make and receive calls.

To answer your first question about having to need the internet for sip calls, that is correct.  Without the internet, you will not be able to make or receive calls on that number.

The second issue from your post, wondering if they know who they are calling.  This is setup in the contact list on the line.  This allows you to dictate the parameters of an incoming call.  You can setup the contact list to dial which phones you would like to receive calls on the pstn line.  You can also setup  fallback dial plan to work if the internet does go out.

Regarding the first point I've probably not been enough clear in my exposition. Here is (I hope) a clearly explanation:
the SRP52x connects the "Line 1" phone to the "FXO" line in two cases: when there is no power (I.E. when you detach the power cord from the outlet) and when there is no active SIP registration (for example if you make a mistake while writing your SIP account credentials or, simplier, when the Internet connection goes down). This feature is expected, is what everyone is looking for and it's basically CORRECT.

The problem I'm asking help for is when everything goes right (power is available, SIP credentials are corrected and Internet is on): what happens to the calls coming from the FXO connected line? They simply remain unanswered and THIS IS ABSOLUTELY NOT ACCEPTABLE. A sample will clarify what I mean:
my FXO line number, known to everyone, is 0526013529. Then I sign a contract with a SIP Provider that gives me the number 0526357668. When there is no power at the SRP52x router and before I configure the new SIP account, all calls directed to 0526013529 come to the phone connected to "Line 1". BUT, when I configure the SIP account for the number 0526357668, ONLY calls directed to this number come to the "Line 1" connected phone, while all the calls directed to the 0526013529 number ring forever, giving to the caller the (wrong) sensation that no one is working here!
What I'm asking for is to LET INCOMING CALLS FROM FXO LINE COME IN ANYWAY (to  the "Line 1" connected phone).

I also require this feature, i am trying rationalising my Router, SPA9000 & SPA400 and a few SIP phones into one device, i have ordered a SRP527W and reading this forum i think i have made a mistake, i also use BT for POTS (free evening calls) and a SIP provider for cheaper international calls. i require both line to receive incoming calls all the time. call routing would also need to be added to be a useful system. i think the lack of a good opps and maintenance manual has caused this problem. is this a FW change will it be possible in the future? if not i will be sending the device back.

I apply a little logic, how will customers know a business has no power and dial a different number? Surly both the internet SIP and POTS PSTN incoming numbers should be active and the POTS number always works no matter what happens.

Hi Davicar

I have purchased this router to be able to selectively used VoIP or PSTN. Once I assign and enable any VoiP accounts, inbound calls on the PSTN lines are no longer ringing or passed through.

Please kindly fix this issue with a new firmware.

While I understand the PSTN becomes active if the router is no longer powered, I need the ability to answer any inbound PSTN calls at any time.



Hi further to my post:

Can CISCO support clarify the following:

Is the FXS connected to FXO by a relay that makes the connection ONLY when the power is down?

In that case this router is pretty useless and a firmware update is unlikely to fix the issue.

Please advise, so I can return the router to my supplier and ask for a refund, as the product is not fit for purpose.

Hi All,

The correct details are included in this thread already.

For the SRP520, the Line port is provided for life line (i.e. when you need to make an outbound emergency call) only.

Power out or no registration causes a physical connection between phone 1 and line ports, meaning that line 1 can be connected to either the SIP account or the PSTN line.  There is no selective call routing with this product.

The SRP520 does not include FXO termination circuitry, so there is no possibility that a firmware upgrade will change this behaviour.

The SPA3102 can provide the call handling functionality that you are looking for here.