This commit introduces CSFB (circuit switched fall-back) capabilities to
srsLTE. Actually, all the eNB has to do is to send a
RrcConnectionRelease with the RedirectedCarrierInfo IE.
The MME triggers this by the S1AP CS Fallback Indicator IE, which may
be present either in the Initial Context Setup Requst or in the
UE Context Modification Request.
As srsLTE has no support for the UE Context Modification Request at all
yet (!), basic support for this message is introduced in this patch.
Both Mobile Originated and Mobile Terminated CSFB with a coupel of
different UE models have been verified using this patch in a setup
consisting of srsENB attached to an undisclosed EPC connected via SGsAP
to a complete Osmocom 2G network.
Closes: #358Closes: #363
Harald Welte
Francisco Paisana