Overview

As of writing this article, the only official documentation related to registering SIP clients with private Telekom.de landlines can be found here (archived version here).

The purpose of this article is to document for everyone interested in this topic (as well as for my future self) the configuration settings necessary to add these phone lines as trunks to FreePBX for inbound and outbound calls. There are a lot of incomplete, outdated, and non-functional configuration examples all across the internet. The settings documented below are what works for me as of writing this post and have been tested with multiple trunks and accounts.

FreePBX configuration

Add Trunk

1. Log into the FreePBX admin interface
2. Navigate to Connectivity > Trunks
3. Click on Add Trunk > Add SIP (chan_pjsip) Trunk

Configure TLS transport

1. Navigate to Settings > Asterisk SIP Settings
2. In the General SIP Settings tab, ensure the following configuration values:
   1. Security Settings
      1. Allow Anonymous Inbound SIP Calls > No
      2. Allow SIP Guests > Yes
      3. Default TLS Port Assignment > PJSip
   2. NAT Settings
      1. External Address > set this to your fixed public IP address (if you have one), otherwise ignore this setting
      2. Local networks > make sure to add your local network CIDRs here (e.g., 192.168.178.0/24)
   3. Everything else can be left on default values and/or empty
3. Go to the SIP Settings [chan_pjsip] tab
4. In the tls section, set tls - {freepbx_ip} - {interface_name} (e.g., tls - 10.100.20.10 - eth0) to Yes
5. Submit the configuration and restart FreePBX

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Trunk configuration

General

On this config page, the number for the line you want to add needs to be in local/regional format, i.e., 0301234567, not in international format (+49301234567).

Setting	Value
Trunk Name	Telekom-0301234567
Hide CallerID	No
Outbound CallerID	0301234567
CID Options	Allow Any CID
Maximum Channels	2
Asterisk Trunk Dial Options	T and System
Continue if Busy	No
Disable Trunk	No
Monitor Trunk Failures	(empty) and No

Dial Number Manipulation Rules

This needs only to be configured if the dialed number needs to be changed before sending it out the trunk, for example, in cases where you have multiple trunks configured and use a dial prefix on your phone to select the desired outbound line.

Don’t change anything here if you don’t know what you’re doing.

pjsip Settings

This is where the interesting stuff happens. All phone numbers entered in the following three sections need to be in * international format*, i.e., +49301234567.

General

Setting	Value
Username	+49301234567
Auth username	(empty; automatically uses value from Username field)
Secret	mySecretTelekomPassword (use your Kundencenter password here, i.e., the one you use to log into the Telekom.de website to view your invoices, not your router or PPPoE password)
Authentication	Outbound
Registration	Send
Language Code	Default
SIP Server	tel.t-online.de
SIP Server Port	(empty to use default port 5060)
Context	from-pstn
Transport	{freepbx_ip}-tls (if you cannot select this, check the Configure TLS transport section again)

Advanced

Setting	Value
DTMF Mode	RFC 4733
Permanent Auth Rejection	Yes
Forbidden Retry Interval	30
Fatal Retry Interval	30
General Retry Interval	60
Expiration	480
Max Retries	10
Qualify Frequency	60
Outbound Proxy	sip:tel.t-online.de\;lr (The \;lr is especially important here as it forces the route URI to use loose routing. If this is not included, the connections will fail!)
User = Phone	Yes
Contact user	+49301234567
From Domain	tel.t-online.de
From User	+49301234567
Client URI	(empty)
Server URI	(empty)
Media Address	(empty)
AOR	(empty)
AOR Contact	(empty)
Match (Permit)	(empty)
Support Path	No
Support T.38 UDPTL	No
T.38 UDPTL Error Correction	None
T.38 UDPTL NAT	No
T.38 UDPTL MAXDATAGRAM	(empty)
Fax Detect	No (unless this is your fax line, in which case you can set this to Yes)
Trust RPID/PAI	No
Send RPID/PAI	No
Send Private CallerID Information	No
Match Inbound Authentication	Default
Inband Progress	Yes
Direct Media	No
Rewrite Contact	Yes
RTP Symmetric	Yes
Media Encryption	SRTP via in-SDP (recommended)
Force rport	Yes
Message Context	(empty)

Codecs

Enable the following codecs and bring them in exactly this order:

1. g722
2. alaw
3. ulaw
4. gsm
5. g726

Disable everything else.

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Inbound Routes configuration

1. Navigate to Connectivity > Inbound Routes
2. Click on Add Inbound Route
3. Configure the inbound route as follows:

General

Setting	Value
Description	Telekom 0301234567 (or anything you like)
DID Number	+49301234567 (international format)
CallerID Number	(empty, defaults to ANY)
CID Priority Route	No (only change if necessary and you know what you’re doing)
Alert Info	None
Ringer Volume Override	None
CID name prefix	(empty, unless you have multiple lines / trunks and need to be able to distinguish between them on your phone)
Music On Hold	Default (or any other playlist you have configured)
Set Destination	configure your inbound route destination here

Advanced

Setting	Value
Indication Zone Country	Default
Signal RINGING	No
Reject Reverse Charges	No
Force Answer	No
Pause Before Answer	(empty)

Privacy

Configure as necessary.

Fax

Configure as necessary in case you want to use one of your phone numbers as a fax line. In this case, the Fax Detect option for the respective trunk needs to be set to Yes (Trunk configuration > pjsip Settings > Advanced).

Other

Configure as necessary.

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Outbound Routes configuration

1. Navigate to Connectivity > Outbound Routes
2. Click on Add Outbound Route
3. Configure the outbound route as follows:

Route Settings

Setting	Value
Route Name	give your route a name
Route CID	(empty)
Override Extension	as necessary, default No
Route Password	as necessary, default (empty)
Route Type	as necessary, default none selected
Music On Hold	select playlist as necessary or leave on default
Time Match Time Zone	Use System Timezone
Time Match Time Group	leave ---Permanent Route--- option, or change as necessary
Trunk Sequence for Matched Routes	add your previously configured trunk(s) here to be used for outbound call routing
Optional Destination on Congestion	leave Normal Congestion, or change as necessary

Dial Patterns

If this is your default outbound route, the most basic outbound dial patterns would be as follows:

( prepend )	prefix |	[ match pattern /	CallerID ]
+49	0	ZX.
+	00	ZX.

Refer to the included documentation in FreePBX on how to configure the dial patterns for your specific use case.

Everything else

Configure Notifications and Additional Settings as necessary, or leave them on default values.

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