neels has posted comments on this change. ( https://gerrit.osmocom.org/c/osmo-msc/+/31740 )

Change subject: do CN CRCX first ......................................................................

Patch Set 1:

(2 comments)

Commit Message:

https://gerrit.osmocom.org/c/osmo-msc/+/31740/comment/ff9b5b10_eb74cb20 PS1, Line 13: Update the voice call sequence chart to show the effects. for convenience, renderings of the voice call charts before and after this patch: https://people.osmocom.org/neels/ohGhe5ah/voice_call_full.before.png https://people.osmocom.org/neels/ohGhe5ah/voice_call_full.after.png

note how the CN CRCX happens first, before sending the first RTP related MNCC, so that this first MNCC can already contain the correct RTP port of the MGW towards CN.

On the MO side we see the CN CRCX OK establishing the RTP port before MNCC_SETUP_IND towards MNCC is sent.

On the MT side we see the CN CRCX OK happens before MNCC_RTP_CREATE goes back to the MNCC. It also shows that the MNCC_CALL_CONF_IND happens before that CRCX OK, because the CALL_CONF_IND does not yet contain RTP or codecs information.

These charts were made (a long time ago) with some script of mine that automatically scrapes the osmo-msc log to create an .msc ladder diagram.

(maybe i should run this again now, since the patches have changed a bit. I don't expect any difference, but I guess I should confirm that.)

File src/libmsc/gsm_04_08_cc.c:

https://gerrit.osmocom.org/c/osmo-msc/+/31740/comment/82047761_1ffb3d9f PS1, Line 901: /* Directly ack with MNCC_CALL_CONF_IND, not yet containing SDP or RTP IP:port information. */ (here is that MT MNCC_CALL_CONF_IND that has no RTP nor SDP yet)