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Diffstat (limited to 'doc/handover-inter-bsc-mt.msc')
| -rw-r--r-- | doc/handover-inter-bsc-mt.msc | 154 |
1 files changed, 154 insertions, 0 deletions
diff --git a/doc/handover-inter-bsc-mt.msc b/doc/handover-inter-bsc-mt.msc new file mode 100644 index 000000000..88a52daa7 --- /dev/null +++ b/doc/handover-inter-bsc-mt.msc @@ -0,0 +1,154 @@ +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"]; +} |