Categories
GSM Mobile Networks RF

GSM with Osmocom Part 9: Calls & SMS at last!

So now we’ve covered the basics of what’s involved let’s get some traffic on our network.

For starters we’ll need to start each of our network elements and bring up whichever BTS hardware we’re using.

In order for our calls to have audio, we’ll need to set a parameter on the Media Gateway. We’ll cover the Media Gateway in more detail down the line, but there’s one value in the MGW we’ll need to set in order to have calls working, and that’s the rtp bind-ip value.
You can either set it in the config file or via VTY/Telnet on port 4243.

We’ve talked about using systemctl to start all the services, but there’s a script in the /etc/osmocom directory called osmocom-all.sh which starts all the network elements for us.

Once you’ve got all the services started I’d suggest hopping onto the OsmoBSC and enabling all the logging you can, then connecting / starting your BTS.

You should see the Abis over IP connection & OML link come up as the BTS connects to the BSC.

And then, hold your breath, power up a phone and search for networks.

All going well you’ll see OsmoMSC in the network search, select it and you should see log data flying by as the phone (“terminal”) connects to the network.

Assuming you configured the IMSI of the SIM on the HLR you should be connected to the network and showing bars on the phone.

You can check your phone number (MSISDN) by dialling the USSD code *#100#

But it’s not a network with just one phone connected, connect a second phone, check it’s phone number the same way and call from one to the other.

SMS should also just work.

And there you have it, a functional GSM network!

But this isn’t the end for us, it’s really just the beginning.

There’s still so much more to learn and work on – Over the next few weeks / months we’ll add packet data to the network with GPRS or EDGE, connect into external call routing and SMS routing interfaces, use Circuit Switched Fallback to provide voice service to users on LTE networks and roam between them.

One reply on “GSM with Osmocom Part 9: Calls & SMS at last!”

Leave a Reply

Your email address will not be published. Required fields are marked *