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msc {
hscale=3;
ms [label="MS via 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="inter-BSC Handover, from remote BSS"];
bsc_gscon <= mgw_msc [label="N-Connect: BSSMAP Handover Request"];
bsc_gscon box bsc_gscon [label="bsc_subscr_con_allocate()"];
bsc_gscon abox bsc_gscon [label="ST_HANDOVER_MT_WAIT_LCHAN"];
bsc_gscon box bsc_gscon [label="lchan_select_by_chan_mode()"];
bsc_lchan <- bsc_gscon [label="lchan_activate(lchan, FOR_HANDOVER)"];
bsc_lchan abox bsc_lchan [label="LCHAN_ST_WAIT_TS_READY"];
...;
--- [label="on no lchan, lchan FSM error or timeout"];
bsc_lchan -> bsc_gscon [label="GSCON_EV_LCHAN_ALLOC_ERROR"];
bsc_gscon box bsc_gscon [label="handover_end(fail)"];
bsc_gscon => mgw_msc [label="BSSMAP Handover Failure"];
ms note bsc_gscon [label="MS happily continues on the old lchan."];
--- [label="END: 'on error'"];
...;
--- [label="IF lchan FSM decides that it is an lchan for speech"];
bsc_lchan abox bsc_lchan [label="LCHAN_ST_WAIT_MGW_ENDPOINT_AVAILABLE"];
bsc_lchan -> bsc_gscon [label="GSCON_EV_ENSURE_MGW_ENDPOINT"];
bsc_gscon abox bsc_gscon [label="ST_HANDOVER_\nWAIT_CRCX_BTS"];
bsc_gscon box bsc_gscon [label="handover_created_mgw_endpoint = true"];
bsc_gscon -> bsc_mgcp [label="mgcp_conn_create()"];
bsc_mgcp => mgw_msc [label="CRCX (for BTS)"];
bsc_mgcp abox bsc_mgcp [label="ST_CRCX_RESP (MGCP_MGW_TIMEOUT = 4s)"];
bsc_gscon note bsc_mgcp [label="conn FSM relies on mgcp FSM timeout"];
...;
--- [label="On Timeout"];
bsc_mgcp note bsc_mgcp [label="On timeout, 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 error 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 -> bsc_mgcp [label="mgcp_conn_delete()"];
bsc_gscon box bsc_gscon [label="handover_end(fail)"];
bsc_gscon => mgw_msc [label="BSSMAP Handover Failure"];
ms note bsc_gscon [label="MS happily continues on the old lchan."];
--- [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 -> bsc_lchan [label="LCHAN_EV_MGW_ENDPOINT_AVAILABLE"];
bsc_lchan abox bsc_lchan [label="LCHAN_ST_WAIT_ACTIV_ACK"];
bsc_gscon note bsc_gscon [label="MSC-side CRCX needs from Handover Required the RTP IP address
and port of the MSC's MGW; from MGW CRCX ACK (BTS) the conn->user_plane.mgw_endpoint; The
Call-ID, which we actually derive from the SCCP connection ID"];
bsc_gscon abox bsc_gscon [label="ST_HANDOVER_MT_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_mgcp note bsc_mgcp [label="On timeout, the MGCP FSM will terminate, emitting the parent_term
event set upon mgcp_conn_create():"];
bsc_mgcp -> bsc_gscon [label="GSCON_EV_MGW_FAIL_MSC"];
bsc_gscon note bsc_gscon [label="GSCON_EV_MGW_FAIL_MSC is handled by the conn FSM allstate
handler. It sets conn->user_plane.fi_msc = NULL."];
bsc_gscon -> bsc_lchan [label="LCHAN_EV_RELEASE"];
bsc_gscon -> bsc_mgcp [label="mgcp_conn_delete() (FSM for BTS)"];
bsc_gscon box bsc_gscon [label="handover_end(fail)"];
bsc_gscon => mgw_msc [label="BSSMAP Handover Failure"];
ms note bsc_gscon [label="MS happily continues on the old lchan."];
--- [label="END: 'On Timeout'"];
...;
bsc_mgcp <= mgw_msc [label="CRCX OK (for MSC)"];
bsc_gscon <- bsc_mgcp [label="GSCON_EV_MGW_CRCX_RESP_MSC"];
bsc_gscon abox bsc_gscon [label="ST_HANDOVER_MT_WAIT_LCHAN"];
--- [label="END: chan_mode a speech mode?"];
--- [label="END: lchan FSM decides that it is an lchan for speech"];
...;
...;
bsc_lchan note bsc_lchan [label="TODO: when does the MS send RLL Establish Ind? I guess like
this:"];
bsc_lchan abox bsc_lchan [label="LCHAN_ST_WAIT_RLL_ESTABLISH"];
ms => bsc_lchan [label="RLL Establish Ind"];
bsc_lchan abox bsc_lchan [label="LCHAN_ST_ACTIVE"];
bsc_lchan -> bsc_gscon [label="GSCON_EV_LCHAN_ACTIVE"];
bsc_gscon abox bsc_gscon [label="ST_HANDOVER_MT_\nWAIT_HO_ACCEPT\nsanity timer?"];
bsc_gscon box bsc_gscon [label="Compose RR Handover Command"];
bsc_gscon => mgw_msc [label="BSSMAP Handover Request Acknowledge"];
mgw_msc note mgw_msc [label="MSC forwards the RR HO Cmd to the remote BSS"];
...;
--- [label="On timeout"];
bsc_lchan <- bsc_gscon [label="NEW lchan: LCHAN_EV_RELEASE"];
ms <=> bsc_lchan [label="release procedure (async)"];
bsc_gscon box bsc_gscon [label="handover_end(fail)"];
bsc_gscon abox bsc_gscon [label="ST_WAIT_CLEAR_CMD"];
bsc_gscon => mgw_msc [label="BSSMAP Clear Request"];
bsc_gscon -> bsc_mgcp [label="mgcp_conn_delete()"];
ms note bsc_gscon [label="MS happily continues on the old lchan."];
--- [label="END: On timeout"];
...;
ms => bsc_gscon [label="RR Handover Accept"];
bsc_gscon => mgw_msc [label="BSSMAP Handover Detect"];
mgw_msc note mgw_msc [label="MSC switches call to new path"];
bsc_gscon abox bsc_gscon [label="ST_HANDOVER_MT_WAIT_SABM\nT3105"];
...;
ms => bsc_gscon [label="SABM"];
bsc_lchan note bsc_lchan [label="SABM: Layer 2 message containing ?"];
bsc_gscon abox bsc_gscon [label="ST_HANDOVER_MT_\nWAIT_MDCX_BTS\nT?"];
bsc_lchan note bsc_lchan [label="TODO: what is UA?"];
ms <= bsc_gscon [label="RR UA"];
bsc_gscon note bsc_gscon [label="TODO: at what point do we know the information needed for BTS
MDCX?"];
bsc_gscon -> bsc_mgcp [label="mgcp_conn_modify()"];
bsc_mgcp abox bsc_mgcp [label="ST_MDCX_RESP"];
bsc_mgcp => mgw_msc [label="MDCX (for BTS)"];
...;
--- [label="Should the Handover Complete arrive early"];
ms => bsc_gscon [label="RR Handover Complete"];
bsc_gscon box bsc_gscon [label="handover_complete_received = true"];
---;
...;
--- [label="On timeout of the mgcp FSM"];
bsc_gscon note mgw_msc [label="MGCP FSM terminates"];
bsc_gscon <- bsc_mgcp [label="GSCON_EV_MGW_FAIL_BTS"];
bsc_lchan note bsc_gscon [label="The phone has already taken on the new lchan, but now we happen
to not be able to use it. The only sensible thing is to end the conn."];
bsc_gscon abox bsc_gscon [label="ST_WAIT_CLEAR_CMD"];
bsc_gscon => mgw_msc [label="BSSMAP Clear Request\n(Equipment Failure)"];
bsc_lchan <- bsc_gscon [label="NEW lchan: LCHAN_EV_RELEASE"];
ms <=> bsc_lchan [label="release procedure (async)"];
bsc_gscon -> bsc_mgcp [label="mgcp_conn_delete()"];
--- [label="END: On timeout of the mgcp FSM"];
...;
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"];
--- [label="IF !handover_complete_received"];
bsc_gscon abox bsc_gscon [label="ST_HANDOVER_MT_WAIT_HO_COMPL\nT?"];
--- [label="ELSE"];
bsc_gscon -> bsc_gscon [label="gscon_handover_post_complete()"];
---;
...;
ms => bsc_gscon [label="RR Handover Complete"];
bsc_gscon box bsc_gscon [label="gscon_handover_post_complete()"];
bsc_gscon => mgw_msc [label="BSSMAP Handover Complete"];
bsc_gscon note bsc_gscon [label="handover_end(success), conn->ho = NULL"];
bsc_gscon abox bsc_gscon [label="ST_ACTIVE"];
}
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