3G voice broken with ALu 9361 femto
I am trying to create a setup with various Osmocom components to get the Alcatel-Lucent 9361 femtocells I have to function as a small 3G network. Currently, I am experiencing issues with 3G voice calls, quite similar to the ones described in #3411 / #2459 / #1937: the voice call is dropped.
I have traced the issue to the following code: https://github.com/osmocom/osmo-mgw/blob/9aaaab6b3b5a541a6c17077f5f1f8bc00ba77152/src/libosmo-mgcp/mgcp_network.c#L873
The femtocell rejects the IuUP message due to a CRC mismatch and indeed, when the bytes are patched, the header CRC is not updated and therefore cannot match.
Thanks a lot for your detailed bug report. The lack of proper IuUP support has been
haunting us for a long time. I once started to implement the related state machines
in libosmocore, see the 'laforge/iu_up' branch. However, nobody has yet found the time
or resources to integrate that properly into osmo-mgw and test it :/