Telekom - multiple SIP-Trunks

Hi all,

I’m new here, and I’m facing some issues with two Telekom SIP Trunks on PBXAct (latest version 12.7.6-2002-2.sng7 with asterisk 16.6.2).

I have configured both trunks as CHAN_SIP, and they are working fine, for a while. Every few weeks both trunks become unavailable and stop working.

I called the telekom support already multiple times, and last time they said, that the problem is, that both sip trunks are using the same source port. I checked that, and they might be right about that.

e.g: netstat -alpen | grep 217.0 returns a single row, instead of two:
tcp 0 0 192.168.XXX.XXX:42454 217.0.XX.XX:5060 VERBUNDEN 995 27454 2588/asterisk

Is there a possibility to split the sip trunks, so that they use two different tcp connections?
I thought about adding a different IP, but I do not think, that this might work and it would be a really bad workaround in production.

I really would appreciate some help on this.

Kind regards

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It depends on what your ITSP is expecting.

In one configuration, the ITSP sends multiple numbers on a single trunk. When this is the case, you configure a single trunk (per IP address) and let the Inbound Route sort the calls by incoming DID (your phone numbers).

In the other configuration, the ITSP sends a single phone number on each trunk. In this configuration, you need to set up a trunk each for each of the connections. Normally, the trunk configuration is differentiated by a username/password/IP address combo.

Asterisk works very well with the first setup, so if you can get your ITSP to send all of your calls on a single trunk, you can set that up easily. It avoids the system getting confused about which trunk it’s using, since the trunk becomes the conduit for all of your calls, and trunks can handle a theoretically limitless number of calls at a time.

In the second setup, it possible for Asterisk to switch the trunks around because the source and destination addresses are the same. Chan-SIP is also known for locking up when this kind of traffic happens.

As a first step, I’d set up your trunk(s) using PJ-SIP. This will get you away from some of the problems you are seeing with the trunks locking up. Many people on the forums have had similar issues, so it would also be a good idea to look back through the old forum posts using the search function at the top of the page.

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thanks for your reply.

I have two sip trunks configured with multiple numbers on each of them.
e.g.: +49123456-XX and +49567891-XX

Both of them have their own telekom sip trunk credentials and their own registration string.
Futhermore the configuration varies based on the different phone numbers.
Of course, everything else is the same.

The german telekom is really inflexible about their configuration. They want me to use different ports for each trunk, but I cannot configure that.

About PJSIP:
I tried setting up pjsip with tcp more than a dozen times in the last year. It never worked out for me. It always registers, but nothing works.
I would assume that it fails, because our phone system runs on an internal ip address and pjsip cannot work with NAT. It also looks to me, that it redirects the traffic to the wrong port on the public ip address, instead of the NAT port.

I searched already through different forums and the different issues with the telekom sip trunk, but I could not find anything, that describes my problem with the pjsip trunk or where the issue discussed and the solution resembles any mistakes in my configuration.

Furthermore all examples how to configure it, are not working for me.

Some more Information about my PJSIP configuration. Maybe someone might find an error in it.


Unless your provider expressly told you to do otherwise, UDP is your only choice for anything on your trunks.

Telekom only supports tcp trunks.

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I just heard from our telekom sales contact, that the Telekom wants to offer something called CompanyFlex in the second half of 2020.

This is different, because I can register multiple and different phone numbers / blocks on the same trunk.

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Anyone here, who can help me with my pjsip trunk on nat, or with my current problem with my two trunks?
I do not want to believe, that I’m the only one, who has one of these issues with the telekom.

I really would appreciate some help on this.

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