Using 1und1 sip with FreeSWITCH

As we are currently in Corona times, I wanted to set up an instance of BigBlueButton (BBB) for our marching band, so that we can have board meetings without meeting in person.

Due to the limited internet access in some villages in the area here, I also wanted to provide a phone dial-in, so board members with slow internet connections could also join the meetings.

BBB uses FreeSWITCH internally for audio routing and it supports connecting a SIP account for dial-in. I am using 1und1* for my internet and phone service, so I wanted to use one of my numbers as dial-in number for BBB. Unfortunately 1und1 is a bit picky with the SIP settings it supports, just using my phone number and password was not enough. I would always get the following error message:

"403: Contact User und Anrufernummer verschieden"

Searching the net for the error message lead me to this old mail from 2012, with no solution. But it had the helpful information, that the contact-user header was not properly set for 1und1. Searching a bit more I found the correct configuration:

  <gateway name="">
    <param name="proxy" value=""/>
    <param name="username" value="4929719000000"/>
    <param name="password" value="YourSuperSecretPassword"/>
    <param name="register" value="true"/>
    <param name="extension" value="4929719000000"/>
    <param name="extension-in-contact" value="true"/>

The important part is, that you need to specify your phone number in international format, both as username and as extension and set the extension-in-contact property to true. This configures FreeSWITCH to send the messages in a way that 1und1 expects.

I have a fully working dial-in to BBB now with one of my existing phone numbers, without any additional cost.

* Affiliation link, supporting our marching band