SMF integration with a third-party UPF

Q/A
,
#1

I’m trying to integrate the SMF function from free5GC with an UPF from Open5GCore. Similar problem has been mentioned in the network-instance-ie-encoding/866 topic. Encoding issue has been resolved as suggested there. Unfortunately, yet another problem occurs when PDU session is being established. UPF throws a segmentation fault. Did anyone have a similar issue and ultimately manage to integrate both solutions? Thanks for your help in advance.

Before adding nwInstFqdnEncoding: true to SMF config:

::pfcp_decode_network_instance_dup():232> network_instance is in wrong format! ::pfcp_decode_network_instance_dup():232> network_instance is in wrong format!

After adding nwInstFqdnEncoding: true to SMF config. Encoding problem disappeared but still there’s a segmentaion fault.

Segmentation fault (core dumped)

#2

Usually, a segfault is caused by the network function accessing a struct field without checking its presence.
If 3GPP spec defines the field as optional, the receiving network function must be able to handle its absence.

If 3GPP spec defines the field as mandatory, you can file a bug with the sending network function.
Nevertheless, the receiving network function should still be robust against malformed input.
Often, the 3GPP spec defines what to do with malformed input, which is typically a negative response, not crashing.

To debug segfaults:

  1. Use dumpcap to capture the traffic around the crashing network function.
  2. Run the problematic network function under gdb debugger.
  3. When the segfault occurs, check the backtrace to tell where it’s happening.
  4. Read the source code side-by-side with the packet that caused the crash.