osmo-bsc/doc/assignment.msc

msc {
	hscale=3;
	ms [label="MS/BTS"], bsc_lchan[label="BSC lchan FSM"],
	bsc_gscon[label="BSC conn FSM"], bsc_mgcp[label="BSC mgcp FSM"], mgw_msc[label="MGW/MSC"];

	ms note mgw_msc [label="lchan allocation sequence for BSSMAP Assignment Request"];

	bsc_gscon <= mgw_msc [label="BSSMAP Assignment Request"];
	bsc_gscon abox bsc_gscon [label="ST_ASSIGNMENT_\nWAIT_LCHAN"];

	bsc_lchan <- bsc_gscon [label="lchan_select_by_chan_mode(chan_mode)"];
	|||;
	--- [label="IF returned lchan is NULL"];
	bsc_gscon => mgw_msc [label="BSSMAP Assignment Failure"];
	bsc_gscon abox bsc_gscon [label="ST_ACTIVE"];
	---;
	|||;
	bsc_gscon box bsc_gscon [label="store lchan pointer in conn->lchan_for_assignment"];
	bsc_lchan <- bsc_gscon [label="lchan_activate(FOR_ASSIGNMENT)"];
	...;
	|||;
	--- [label="on lchan FSM error or timeout"];
	bsc_lchan -> bsc_gscon [label="GSCON_EV_LCHAN_ALLOC_ERROR"];
	bsc_gscon box bsc_gscon [label="'forget' all about conn->lchan_for_assignment"];
	bsc_gscon => mgw_msc [label="BSSMAP Assignment Failure"];
	bsc_gscon abox bsc_gscon [label="ST_ACTIVE"];
	--- [label="END: 'on error'"];
	...;
	...;

	--- [label="IF lchan FSM decides that it is an lchan for speech"];
	bsc_lchan -> bsc_gscon [label="GSCON_EV_ENSURE_MGW_ENDPOINT"];
	--- [label="IF there is an MGW endpoint for the BTS already (conn->user_plane.fi_bts)"];
	bsc_gscon -> bsc_lchan [label="LCHAN_EV_MGW_ENDPOINT_AVAILABLE"];
	--- [label="ELSE: no MGW endpoint for the BTS side yet"];
	bsc_gscon abox bsc_gscon [label="ST_ASSIGNMENT_\nWAIT_CRCX_BTS"];
	bsc_gscon box bsc_gscon [label="assignment_created_mgw_endpoint = true"];
	bsc_gscon -> bsc_mgcp [label="mgcp_conn_create()"];
	bsc_mgcp abox bsc_mgcp [label="ST_CRCX_RESP (MGCP_MGW_TIMEOUT = 4s)"];
	bsc_mgcp => mgw_msc [label="CRCX (for BTS)"];
	bsc_gscon note bsc_mgcp [label="conn FSM relies on mgcp FSM timeout"];
	...;
	--- [label="On Timeout"];
	bsc_mgcp note bsc_mgcp [label="On timeouit, the MGCP FSM will terminate, emitting the parent_term
		event set upon mgcp_conn_create():"];
	bsc_mgcp -> bsc_gscon [label="GSCON_EV_MGW_FAIL_BTS"];
	bsc_gscon note bsc_gscon [label="GSCON_EV_MGW_FAIL_BTS is handled by the conn FSM allstate
		handler. It sets conn->user_plane.fi_bts = NULL."];
	bsc_gscon -> bsc_lchan [label="LCHAN_EV_MGW_ENDPOINT_ERROR"];
	bsc_lchan note bsc_gscon [label="conn FSM timeout handler exits and relies on the lchan FSM
		signalling error, which should actually happen immediately:"];
	bsc_gscon <- bsc_lchan [label="GSCON_EV_LCHAN_ALLOC_ERROR"];
	bsc_gscon abox bsc_gscon [label="ST_ACTIVE"];
	bsc_gscon box bsc_gscon [label="'forget' all about conn->lchan_for_assignment"];
	bsc_gscon => mgw_msc [label="BSSMAP Assignment Failure"];
	--- [label="END: 'On Timeout'"];
	...;

	bsc_mgcp <= mgw_msc [label="CRCX OK (for BTS)"];
	bsc_mgcp box bsc_mgcp [label="libosmo-mgcp-client fsm_crcx_resp_cb()"];
	bsc_mgcp abox bsc_mgcp [label="ST_READY"];
	bsc_mgcp -> bsc_gscon [label="GSCON_EV_MGW_CRCX_RESP_BTS"];
	bsc_gscon abox bsc_gscon [label="ST_ASSIGNMENT_\nWAIT_LCHAN"];
	bsc_gscon -> bsc_lchan [label="LCHAN_EV_MGW_ENDPOINT_AVAILABLE"];
	--- [label="END: lchan FSM decides that it is an lchan for speech"];
	...;
	...;

	bsc_lchan -> bsc_gscon [label="GSCON_EV_LCHAN_ACTIVE"];
	bsc_gscon abox bsc_gscon [label="ST_ASSIGNMENT_\nWAIT_COMPLETE\nT10, 6s"];
	ms <= bsc_gscon [label="RR Assignment"];
	...;
	--- [label="On Timeout"];
	bsc_gscon => mgw_msc [label="BSSMAP Assignment Failure"];
	bsc_gscon -> bsc_lchan [label="LCHAN_EV_LCHAN_RELEASE"];
	bsc_gscon box bsc_gscon [label="'forget' all about conn->lchan_for_assignment"];
	--- [label="IF assignment_created_mgw_endpoint == true"];
	bsc_gscon -> bsc_mgcp [label="mgcp_conn_delete()"];
	bsc_gscon note bsc_mgcp [label="If the MGW endpoint didn't exist before the Assignment, release
		it now. If there was one before this, it is probably still in use by a previous lchan, so
		keep it in place."];
	bsc_gscon abox bsc_gscon [label="ST_ACTIVE"];
	--- [label="END: 'On Timeout'"];
	...;
	ms => bsc_gscon [label="RR Assignment Complete"];
	bsc_gscon -> bsc_lchan [label="OLD lchan: LCHAN_EV_LCHAN_RELEASE"];
	bsc_gscon box bsc_gscon [label="conn->lchan = conn->lchan_for_assignment"];
	--- [label="IF: chan_mode a speech mode?"];
	bsc_gscon abox bsc_gscon [label="ST_WAIT_MDCX_BTS"];
	bsc_gscon -> bsc_mgcp [label="mgcp_conn_modify()"];
	bsc_mgcp note bsc_mgcp [label="same mgcp FSM as above, for BTS side"];
	bsc_mgcp abox bsc_mgcp [label="ST_MDCX_RESP"];
	bsc_mgcp => mgw_msc [label="MDCX (for BTS)"];
	...;
	--- [label="On Timeout"];
	bsc_gscon -> bsc_lchan [label="LCHAN_EV_RELEASE"];
	bsc_gscon -> bsc_mgcp [label="mgcp_conn_delete()"];
	bsc_gscon => mgw_msc [label="BSSMAP Assignment Failure"];
	bsc_gscon abox bsc_gscon [label="ST_WAIT_CLEAR_CMD"];
	bsc_gscon => mgw_msc [label="BSSMAP Clear Request"];
	--- [label="END: 'On Timeout'"];
	...;
	bsc_mgcp <= mgw_msc [label="MDCX OK"];
	bsc_mgcp abox bsc_mgcp [label="ST_READY"];
	bsc_mgcp -> bsc_gscon [label="GSCON_EV_MGW_MDCX_RESP_BTS"];
	bsc_gscon abox bsc_gscon [label="ST_WAIT_CRCX_MSC"];
	bsc_gscon -> bsc_mgcp [label="mgcp_conn_create()"];
	bsc_mgcp note bsc_mgcp [label="second mgcp FSM for MSC side"];
	bsc_mgcp => mgw_msc [label="CRCX (for MSC)"];
	...;
	--- [label="On Timeout"];
	bsc_gscon -> bsc_lchan [label="LCHAN_EV_RELEASE"];
	bsc_gscon -> bsc_mgcp [label="mgcp_conn_delete()"];
	bsc_gscon => mgw_msc [label="BSSMAP Assignment Failure"];
	bsc_gscon abox bsc_gscon [label="ST_WAIT_CLEAR_CMD"];
	bsc_gscon => mgw_msc [label="BSSMAP Clear Request"];
	--- [label="END: 'On Timeout'"];
	...;
	bsc_mgcp <= mgw_msc [label="CRCX OK (for MSC)"];
	bsc_gscon <- bsc_mgcp [label="GSCON_EV_MGW_CRCX_RESP_MSC"];
	--- [label="END: chan_mode a speech mode?"];

	bsc_gscon => mgw_msc [label="BSSMAP Assignment Complete"];

	bsc_gscon abox bsc_gscon [label="ST_ACTIVE"];
}