lchan_rtp_fsm: Deferr IPACC MDCX after BTS side MGCP MDCX

This is needed to be able to force MGW to provide an IPv4 address during
MDCX, since IPACC protocol on the BTS side only supports IPv4, but one
may need IPv6 side at the same time on the core side.
By moving the IPACC MDCX request to a later step, the BSC gains
knowledge of the local address on each side (BTS, MGW), and if they
don't match (ie. BTS uses IPv4 and MGW uses IPv6), it can then get MGW
to offer an IPv4 address during MGCP MDCX containing the BTS IPv4
address. At that point, the MGW can see the mismatch and provide an IPv4
address in the MGCP MDCX ACK, which can then finally be communicated to
the BTS during IPACC MDCX phase.

Previous order:
BSC -> MGW: CRCX
BSC <- MGW: CRCX ACK		(get MGW local IP addr)
BSC -> BTS: IPACC CRCX
BSC <- BTS: IPACC CRCX ACK 	(get BTS local IP addr)
BSC -> BTS: IPACC MDCX 		(set MGW IP addr)
BSC <- BTS: IPACC MDCX ACK
BSC -> MGW: MDCX 		(set BTS IP addr)
BSC <- MGW: MDCX ACK

New order:
BSC -> MGW: CRCX
BSC <- MGW: CRCX ACK 		(get MGCP local IPv6 addr)
BSC -> BTS: IPACC CRCX
BSC <- BTS: IPACC CRCX ACK 	(get BTS local IPv4 addr)
BSC -> MGW: MDCX 		(set BTS IPv4 addr)
BSC <- MGW: MDCX ACK 		(here MGW changes its local addr to IPv4)
BSC -> BTS: IPACC MDCX 		(set MGW IPv4 addr)
BSC <- BTS: IPACC MDCX ACK

Change-Id: I4de5ea5c94c1482c9cb0b6386997a942edc60e32

2 files changed, 10 insertions, 7 deletions

diff --git a/doc/lchan-rtp-fsm.dot b/doc/lchan-rtp-fsm.dot
index d5df643b5..4c2dd31bf 100644
--- a/doc/lchan-rtp-fsm.dot
+++ b/doc/lchan-rtp-fsm.dot
@@ -1,7 +1,7 @@
 digraph G {
 rankdir=TB
 labelloc=t; label="lchan RTP FSM"
-	
+
 	lchan [label="lchan\nFSM",shape=box3d]
 	lchan2 [label="lchan\nFSM",shape=box3d]
 	ho_as [label="Handover or Assignment FSM",shape=box3d]
@@ -23,14 +23,15 @@ labelloc=t; label="lchan RTP FSM"
 	lchan -> WAIT_LCHAN_READY [label="LCHAN_RTP_EV_LCHAN_READY",style=dashed]
 	WAIT_LCHAN_READY -> WAIT_IPACC_CRCX_ACK [label="IPACC BTS"]
 	WAIT_LCHAN_READY -> WAIT_READY_TO_SWITCH_RTP
-	WAIT_IPACC_CRCX_ACK -> WAIT_IPACC_MDCX_ACK
-	WAIT_IPACC_MDCX_ACK -> WAIT_READY_TO_SWITCH_RTP
+	WAIT_IPACC_CRCX_ACK -> WAIT_READY_TO_SWITCH_RTP
 	invisible -> ho [label="HO DETECT",style=dashed]
 	ho -> WAIT_READY_TO_SWITCH_RTP [label="LCHAN_RTP_EV_READY_TO_SWITCH",style=dashed]
 	WAIT_READY_TO_SWITCH_RTP -> WAIT_MGW_ENDPOINT_CONFIGURED
 	WAIT_MGW_ENDPOINT_CONFIGURED -> mgwep [label="MDCX",style=dashed]
 	mgwep -> WAIT_MGW_ENDPOINT_CONFIGURED [label="LCHAN_RTP_EV_\nMGW_ENDPOINT_\nCONFIGURED",style=dashed]
+	WAIT_MGW_ENDPOINT_CONFIGURED -> WAIT_IPACC_MDCX_ACK [label="IPACC BTS"]
 	WAIT_MGW_ENDPOINT_CONFIGURED -> RTP_READY
+	WAIT_IPACC_MDCX_ACK -> RTP_READY
 	RTP_READY -> lchan2 [label="LCHAN_EV_\nRTP_READY",style=dashed]
 	RTP_READY -> RTP_ESTABLISHED
 	lchan2 -> RTP_ESTABLISHED [label="LCHAN_RTP_EV_\nRELEASE",style=dashed]
diff --git a/doc/lchan.msc b/doc/lchan.msc
index b0e32d684..9962c77a7 100644
--- a/doc/lchan.msc
+++ b/doc/lchan.msc
@@ -68,10 +68,6 @@ msc {
 	ms <= rtp [label="IPACC CRCX"];
 	...;
 	ms => rtp [label="IPACC CRCX ACK (BTS RTP port info)"];
-	rtp abox rtp [label="LCHAN_RTP_ST_WAIT_IPACC_MDCX_ACK"];
-	ms <= rtp [label="IPACC MDCX (MGW RTP port info)"];
-	...;
-	ms => rtp [label="IPACC MDCX ACK"];
 	--- [label="END ip.access style BTS"];
 	|||;
 	rtp box rtp [label="lchan_rtp_fsm_switch_rtp()"];
@@ -91,6 +87,12 @@ msc {
 	...;
 	mgwep rbox mgwep [label="MGCP: MDCX OK"];
 	rtp <- mgwep [label="LCHAN_RTP_EV_MGW_ENDPOINT_CONFIGURED"];
+	--- [label="IF ip.access style BTS"];
+	rtp abox rtp [label="LCHAN_RTP_ST_WAIT_IPACC_MDCX_ACK"];
+	ms <= rtp [label="IPACC MDCX (MGW RTP port info)"];
+	...;
+	ms => rtp [label="IPACC MDCX ACK"];
+	--- [label="END ip.access style BTS"];
 	rtp abox rtp [label="LCHAN_RTP_ST_READY"];
 	lchan <- rtp [label="LCHAN_EV_RTP_READY"];
 	rtp note rtp [label="RTP FSM stays ready for Rollback until final establish event"];