[srslte-users] VoLTE with srsenb and Amarisoft Callbox IMS

[Englberger, Norbert]

Hi,

we are trying to expand our existing 4G setup by connecting multiple srsenb to our Amarisoft Callbox for Data and Voice services.

Right now, we could connect the eNodeB with the Callbox and Data services (surfing the Internet) work, Voice calls fail.
When we start a Call the UE loses the complete connection to the Network and has to be reconnected manually ( switching to Airplane mode one and off).

After our first analysis of the PCAP files generated by the eNodeB showed a Malformed "E-RABSetupResponse", which could be fixed by reconfiguring the "ims" APN to use IPv4 only.

Since VoLTE still fails, we took a further look into the PCAPs and discovered the following:

No.        Time      Source  Destination        Protocol              Length  Info
1             0.000000                                             S1AP/NAS-EPS 131         InitialUEMessage, Attach request, PDN connectivity request
2             0.000852                                             S1AP/NAS-EPS 33           DownlinkNASTransport, ESM information request
3             0.020218                                             S1AP/NAS-EPS 103         UplinkNASTransport, ESM information response
4             0.020907                                             S1AP/NAS-EPS 226         InitialContextSetupRequest, Attach accept, Activate default EPS bearer context request
5             0.060364                                             S1AP     38           InitialContextSetupResponse
6             0.100302                                             S1AP/NAS-EPS 59           UplinkNASTransport, Attach complete, Activate default EPS bearer context accept
7             7.540231                                             S1AP/NAS-EPS 105         UplinkNASTransport, PDN connectivity request
8             7.540914                                             S1AP/NAS-EPS 131         E-RABSetupRequest, Activate default EPS bearer context request
9             7.540994                                             S1AP     31           E-RABSetupResponse [RadioNetwork-cause=not-supported-QCI-value]
10           15.540146                                           S1AP/NAS-EPS 105         UplinkNASTransport, PDN connectivity request
11           15.540839                                           S1AP/NAS-EPS 34           DownlinkNASTransport, PDN connectivity reject (Multiple PDN connections for a given APN not allowed)


In lines 1-6 the UE connects to the Network and to the APN "internet". This seem to work fine.
Then the UE tries to connect to the APN "ims" and after a while retries to connect, where the second connection is rejected. (Shouldn't there be any "reject" or "accept" message between the two connection requests?)

After we couldn't get VoLTE running with srsenb, we replaced it  with an Amarisoft eNB from a second System (Amarisoft-OTS) and the configuration with the two Amarisoft systems worked.

Maybe someone has more experience in connecting an srsENB to an Amarisoft MME + IMS than me and my team and could give some advice onto  where we have to look at in our configuration to make VoLTE work.

If needed I could provide PCAP and log-files from srsenb and Amarisoft Callbox.

Sincerely

Norbert
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