[MME] s11: Allow CreateSessionResponse with no PAA IE

[pespin]

No description provided.

[pespin]

Don't merge it yet, waiting for @asdfuser to give it a try.

[asdfuser]

It helps, but the TAU still fails because the CreateSessionResponse is missing the S5c TEID (rsp->pgw_s5_s8__s2a_s2b_f_teid_for_pmip_based_interface_or_for_gtp_based_control_plane_interface.presence == 0)

I'm not sure if this can be ignored for the TAU as well or why it's not included in this case.

[pespin]

@asdfuser is the TEID provided during SGSNContextReq/Resp? IIRC it's not, so probably SGW needs to forward it during S11 CreateSessionResp most probably right?

[asdfuser]

@pespin The PDP Context IE contains a "TEID Control Plane" and "TEID Data I" and the spec says the following:

The Uplink Tunnel Endpoint Identifier Control Plane is the Tunnel Endpoint Identifier used between the old SGSN and
the GGSN in up link direction for control plane purpose. It shall be used by the new SGSN within the GTP header of
the Update PDP Context Request message.
The GGSN Address for User Traffic and the Uplink Tunnel Endpoint Identifier Data I are the GGSN address and the
Tunnel Endpoint Identifier used between the old SGSN and the GGSN in uplink direction for user plane traffic on a
PDP context. They shall be used by the new SGSN to send uplink user plane PDU to the GGSN until new GGSN
address for User Traffic is possibly received from GGSN (in Update PDP Context Response).

So I guess it's one of those?

[pespin]

@asdfuser my understanding is that, ffrom the point of view of the MME, if the SGW-C is not providing any of those during CreateSessionResponse, the MME should assume the TEIC and TEID didn't change at the PGW, and hence keep using the ones received from the SGSN. So it's actually fine from the MME not receiving those. Does that make sense to you as well?

[asdfuser]

@pespin Yeah, it does. I have prepared a patch covering that case on my test system, but I can only test it tonight once I'm back home and can operate the test UE.