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Connecting two spa3102. Back2Back config.

This could be a helpful configuration for those who needs to connect two places, lets said in two differents countries, without a PBX to manage the calls. It’s pretty straightforward, but it’s not very safe.

The scenario: Two SPA3102, each one in a different location and connected to a PSTN. I going to skip the basic configuration part (enable web interface, fixed ip address, enable bridge mode).


LINE1 tab

1.- Enable the Line1, the fxs port.

Advanced -> Voice -> Line 1 -> Line Enable -> Yes


2.- Check the port and transport. Could be any port, but remenber because needs to fit with options in the dialplan.

Advanced -> Voice -> Line 1 -> Sip Settings


3.- Enable make and answer call withou registry:

Advanced -> Voice -> Line 1 -> Proxy and Registration

Make Call Without Reg: Yes

Ans Call Without Reg: Yes


4.- Add an user to manage this line: usrLine1Loc01

Advanced -> Voice -> Line 1 ->  Subscriber Information -> User ID


5.- Create a Dialplan to be able to make calls through the remote PSTN, and enable Ip Dialing, this feature will enable the SPA to dial using IP addresses rather than SIP URIs which is ideally what should be used.

Advanced -> Voice -> Line 1 -> Dial Plan




S0 = Dial Immediately

UsrPstnLoc02 = Remote PSTN user = Remote IP

5061= Remote PSTN port



1.- Enable the PSTN, the fxo port.

Advanced -> Voice -> PSTN -> Line Enable -> Yes


2.- Check the port and transport. Should be noted that the port is different of the line1.
Advanced -> Voice -> PSTN -> Sip Settings


3.- Enable make and answer call withou registry:
Advanced -> Voice -> PSTN -> Proxy and Registration

Make Call Without Reg: Yes
Ans Call Without Reg: Yes


4.- Add an user to manage this line: usrLine1Loc01
Advanced -> Voice -> PSTN -> Subscriber Information -> User ID


5.- Create a Dialplan to be able to make calls through the remote PSTN, and enable Ip Dialing, this feature will enable the SPA to dial using IP addresses rather than SIP URIs which is ideally what should be used.
Advanced -> Voice -> PSTN -> Dial Plans

# You could use any dialplan but 1, because most of the default settings are routed to it.

Dial Plan 2: (S0<:Usr-Line1-Loc2@IP-Location02:Port-Line1-Loc02>)

Dial Plan 2: (S0<:UsrLineLoc2@>)


6.- Make sure you are able to make calls from VoIP to PSTN. Besides this we’ll take some security measures, because if we do not, anyone just setting an IP/Soft phone with the SPA IP address will be able to make calls through the PSTN.

Advanced -> Voice -> PSTN -> VoIP-To-PSTN Gateway Setup

VoIP-To-PSTN Gateway Enable: Yes

Line 1 VoIP Caller DP: 1

VoIP Caller Default DP: 1

# Security hardening

VoIP Caller Auth Method: PIN

Should enter a PIN number after a set of beeps to access the PSTN. After 3 failed attempts, cannot reach the PSTN.

VoIP PIN Max Retry: 3

Making an IP address access list to allow the SPA located in Loc2 to bypass the PIN number.

VoIP Access List:

Add the pin number to access

VoIP Caller 1 PIN: 1234


7.-  Make sure you are able to make calls from PSTN to VoIP.

Advanced -> Voice -> PSTN -> PSTN-To-VoIP Gateway Setup

PSTN Ring Thru Line 1: yes

PSTN Ring Thru Line 1: no # Set yes if you want ring the phone locally, you will need a phone in the fxs port.

PSTN Caller Default DP: 2 # Or whatever dialplan number you choose

PSTN CID For VoIP CID: yes # Enable who's calling; Caller ID


8.- Set the delay to PSTN answer the call to 1, with this value the SPA will have enough time to get who is calling, otherwise we won’t know who is calling.

Advanced -> Voice -> PSTN -> FXO Timer Values (sec)

PSTN Answer Delay: 1


9.- Set the Disconnect Tone

Advanced -> Voice -> PSTN ->PSTN Disconnect Detection

US: 480@-30,620@-30;4(.25/.25/1+2)
UK: 400@-30,400@-30; 2(3/0/1+2)
France: 440@-30,440@-30; 2(0.5/0.5/1+2)
Germany: 440@-30,440@-30; 2(0.5/0.5/1+2)
Netherlands: 425@-30,425@-30; 2(0.5/0.5/1+2)
Sweden: 425@-10; 10(0.25/0.25/1)
Norway: 425@-10; 10(0.5/0.5/1)
Italy: 425@-30,425@-30; 2(0.2/0.2/1+2)
Spain: 425@-10; 10(0.2/0.2/1,0.2/0.2/1,0.2/0.6/1) - Telefonica
Portugal: 425@-10; 10(0.5/0.5/1)
Poland: 425@-10; 10(0.5/0.5/1)
Denmark: 425@-10; 10(0.25/0.25/1)
New Zealand: 400@-15; 10(0.25/0.25/1)
Australia: 425@-13; 10(0.375/0.375/1)
Argentina: 425@-30,425@-30;4(.3/.2/1+2)
Venezuela: 425@-30,425@-30;4(.5/.5/1+2) - CANTV

This values is for the local and most used telephones companies, for example in Spain depending on the phone company you will have a different disconnection tone.


The configuration will be the same in both devices, changing the IP address, the users and the values for specific countries if applies.

NOTE: You should open and forward to the device’s IP the following ports in the firewall/router in both sides to allow the communication between the devices.

LINE1: 5060

PTSN: 5061

RTP (voice): From 16384 to 16482. This values could be changed in:

Advance-> Voice -> SIP -> RTP Parameters

There is another way to do this, is configuring a stunserver (could be yours or a public one), doing NAT but this will be for another post.


General – Basic settings

Click to access spa3102_quick.pdf



Connecting Spa

Click to access spa_backtoback_2x_spa3000.pdf



About silvinux

I'm an IT freaky, that love to deploy (free software/ OpenSource) technologies in little projects at my home and this blog is a series of documents/manuals/guides that I've made through time to time.


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