Tag Archives: Home Subscriber Server

Connecting any 3rd Party HSS to Open5GS MME

You may want to connect Open5GS’ MME to a different Home Subscriber Server (HSS),

To do it we need a few bits of information:

  • The Domain Name of the HSS
  • The Realm of the HSS
  • The IP of the HSS
  • The Transport Used (TCP/SCTP)
  • If TLS is used

With these bits of information we can go about modifying the Open5GS MME config to talk to our different HSS.

Edit FreeDiameter Config

The config for the Open5GS MME’s Diameter peers is handled by the FreeDimaeter library,

You can find it’s config files in:


We’ll start by changing the realm to match the realm of the HSS and the identity to match the identity configured as the MME peer on the HSS.

We’ll next set the ListenOn address to be a reachable IP address isntead of just a loopback address,

If you’re using TLS you’ll need to put your certificates and private key files into the TLS config,

Finally we’ll put our HSS details in the Peer Configuration;

Once all this is done we’ll need to restart our MME and you should see the Diameter Capabilities Exchange / Answer commands between the HSS and the MME if all was successful,

systemctl restart open5gs-mmed

In the /var/log/open5gs/mme.log I can now see:

05/11 23:25:46.896: [app] INFO: MME initialize…done (../src/mme/app-init.c:33)
05/11 23:25:46.898: [diam] INFO: CONNECTED TO 'hss.nickexamplenet' (SCTP,soc#15): (../lib/diameter/common/logger.c:108)

And that’s it! We’re connected to an external HSS.

Through the freeDiameter config file you can specify multiple ConnectPeer() entries to connect to multiple HSS (like a pool of them), and requests will be distributed evenly between them.

PyHSS Update – IMS Cx Support!

As I’ve been doing more and more work with IMS / VoLTE, the requirements / features on PyHSS has grown.

Some key features I’ve added recently:

IMS HSS Features

IMS Cx Server Assignment Request / Answer

IMS Cx Multimedia Authentication Request / Answer

IMS Cx User Authentication Request / Answer

IMS Cx Location Information Request / Answer

General HSS Features

Better logging (IPs instead of Diameter hostnames)

Better Resync Support (For USIMs with different sync windows)


There’s still some functions in the 3GPP Cx interface description I need to implement:

IMS Cx Registration-Termination Request / Answer

IMS Cx Push-Profile-Request / Answer

Support for Resync in IMS Cx Multimedia Authentication Answer

Keep an eye on the GitLab repo where I’m pushing the changes.

If you’re leaning about VoLTE & IMS networks, or building your own, I’d suggest checking out my other posts on the topic.