Asterisk with SS7 via Wanpipe, Dahdi and libss7 – with ISUP SAM support

A howto on installing Asterisk with SS7 supported via libss7 on Sangoma hardware along with support for ISUP SAM messages.

After much head banging in bringing up an SS7 link with SAM support, I am documented what worked here.

Firstly, what is SAM support? One end of an SS7 link initialises a new call by sending an Initial Address Message (IAM). All SS7 software stacks support this and usually it’s enough. One case where it’s not enough is when one wants to address a phone number with more than the E.164 standard max length of 16  (usually to pass additional information tacked on the start, end of or even replacing an A or B number). In this scenario, SS7 uses a Subsequent Address Message (SAM) to send the additional digits. Most / all mainstream Asterisk SS7 software stacks do not support this.

The platform and software used is as follows:

  • Ubuntu 10.04 LTS standard CLI install;
  • dahdi-linux-complete-2.4.0 from the archives (direct link);
  • a patched version of libss7 supporting SAM via SVN (see below);
  • a patched version of chan-dahdi via SVN (see below);
  • Asterisk 1.6.0.28 from the archives (direct link);
  • Asterisk Addons 1.6.0.6 from the archives (direct link);
  • Sangoma Wanpipe 3.5.24 (direct link).

Yes, I know some of the above are obsolete. Unfortunately it’s what’s required for everything to play nicely together. And, guess what, it works!

Before You Start

Ensure you have all the necessary packages for building the packages:

You can assume the working directory is /usr/local/src in the following.

Installing dahdi-linux-complete

Download and extract dahdi-linux-complete into /usr/local/src. Then, in the same directory, create some symbolic links:

Now build dahdi-linux:

Now move onto dahdi-tools:

Installing libss7

There is a patched version of Digium’s libss7 referred to as Attila’s libss7 available via SVN. Download and install it:

Installing Asterisk

Download and extract the Asterisk 1.6.0.28 package reference above.

Now this next bit is very important and easy to miss – you also need a patched version of chan_dahdi.c that is compatible with the patched version of libss7. This is also available from SVN:

Then copy it to your Asterisk source:

Now continue with the Asterisk installation:

Install Asterisk Addons (optional)

Download and unpack the above referenced add ons package and build and install:

Sangoma Wanpipe

I’m using one of Sangoma’s E1 / T1 interface cards and so I need Wanpipe also. I’m using version 3.5.24 and preceed as follows after unpacking:

During the install, follow these prompts:

  • select option 2 => Asterisk/Dahdi Support;
  • enter path /usr/local/src/dahdi-linux (for Zaptel path prompt);
  • select defaults for everything else;
  • you DO want to install start-up scripts;
  • you DO to configure wanpipe devices for DAHDI;
  • you DO want to generate /etc/asterisk/chan_dahdi.conf and:
    • select E1 / T1 as appropriate;
    • select line framing and encoding;
    • choose clock source;
    • select Zaptel/Dahdi – PRI CPE as signalling;
    • select National ISDN 2 as switch type;
    • do not enable hardware DTMF detection;
    • use all channels;
    • select dial plan context as appropriate;
  • and continue for other ports as necessary;
  • finally, choose Save cfg: Stop Asterisk & Wanpipe now
  • you would like wanrouter to start on system boot;
  • and you would like to execute ‘dahdi_cfg’ each time wanrouter starts.

Configuration Steps

We now need to set various options in Wanpipe, Dahdi and Asterisk for SS7 as it’s PRI/ISDN by default.

Edit all /etc/wanpipe/wanpipeX.conf files as necessary and change:

to

Now edit /etc/dahdi/system.conf and change (for example):

to

which of course assumes signalling is on channel 1. If you have voice only links, you might need something like:

Lastly, we need to configure Asterisk. Replace lines such as:

with an appropriate configuration. Mine follows below with some edits and some important notes at the end:

  • Set pointcode, adjpointcode and defaultdpc as appropriate;
  • set networkindicator as appropriate and ensure it matches the other end (you can see what you’re being sent and what you’re sending via ss7 debug;
  • cicsbeginwith is normally 1 but the telco on my end are starting at 2 – this was groping in the dark diagnostics and issues such as no audio, CICs not in service when both sides claim they are, etc may point to misaligned CICs;
  • make sure you have configured from-pstn or the appropriate context in yourextensions.conf.

Confirming Your Link Is Up

Now start wanrouter (/etc/init.d/wanrouter start); dahdi (/etc/init.d/dahdi start); and Asterisk (/etc/init.d/asterisk start). You should see your link come up via logs available with the dmesg command. Launch the Asterisk console and check the status of your links:

You should now be okay to make test calls.

Do You Need Professional Support / Consultancy?

While I will try to respond to comments and questions on this blog, I don’t have the time to provide one on one assistance pro-bono. Professional consultancy on Asterisk and SS7 is available worldwide through my company, Open Solutions with contact details here.

References

For posterity, I have added Domjan Attila patched libss7 and chan_dahdi to GitHub: