S1 Paging failure

[RafalArciszewski]

Hi @acetcom,
I am facing a problem with paging procedure on S1 interface with one of eNB from ZTE. Test was done with Open5gs v2.2.8.
After the UEContext is released MME is sending Paging message but this message is send on SCTP stream 0x1. This stream is regarded as 'UE-associatied-signalling'. In fact when I read 3gpp standard it seems that Paging messages should be send as a 'non UE-associatied-signalling' in SCTP stream 0x0.
This ZTE eNB has a strict implementation of SCTP streams and ignores the Paging messages. I had many problems related to SCTP with other EPCs to get connected.

Is it possible to change the MME code that Paging messages are sent as 'non UE-associated-signalling'?

3gpp reference 36.413 point 3.1 Definitions:
UE-associated signalling: When S1-AP messages associated to one UE uses the UE-associated logical S1-connection
for association of the message to the UE in eNB and EPC.
UE-associated logical S1-connection: The UE-associated logical S1-connection uses the identities MME UE S1AP ID
and eNB UE S1AP ID according to definition in TS 23.401 [11]. For a received UE associated S1-AP message the
MME identifies the associated UE based on the MME UE S1AP ID IE and the eNB identifies the associated UE based
on the eNB UE S1AP ID IE. The UE-associated logical S1-connection may exist before the S1 UE context is setup in
eNB.
I understand from above that after UEContextRelease procedure is done the MME and UE S1AP id are gone and Paging should be sent as 'non UE-associated signaling'.
Procedures described in this standard usually has a remark "The procedure uses UE-associated signalling". For Paging there is no such remark.

I attach also the pcaps for reference (one from Open5gs, second from other EPC):

open5gs_paging_fail.zip

d_paging_ok.zip

Regards,
Rafał Arciszewski

[acetcom]

Hi @RafalArciszewski

I agree. So, I've changed to use Non-UE signalling connection when MME/AMF sends paging message.

Thank you so much!
Sukchan

[RafalArciszewski]

Thanks for quick response and commit! I will test it.

Regards,
Rafał

[RafalArciszewski]

It is working now. Thanks!

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