| msc { |
| hscale=3; |
| ms [label="MS"], bts [label="BTS"], bsc[label="BSC"], bsc_gscon[label="BSC conn FSM"], bsc_mgcp[label="BSC mgcp FSM"], mgw[label="MGW"], msc_[label="MSC"]; |
| |
| ms note msc_ [label="lchan allocation sequence for BSSMAP Assignment Request"]; |
| |
| bsc <= msc_ [label="BSSMAP Assignment Request"]; |
| bsc box bsc [label="bssmap_handle_assignm_req()"]; |
| bsc -> bsc_gscon [label="GSCON_EV_A_ASSIGNMENT_CMD"]; |
| |
| --- [label="is the chan_mode a speech mode?"]; |
| |
| bsc_gscon abox bsc_gscon [label="ST_WAIT_CRCX_BTS (MGCP_MGW_TIMEOUT = 4s)"]; |
| bsc_gscon -> bsc_mgcp [label="mgcp_conn_create()"]; |
| bsc_mgcp => mgw [label="CRCX (for BTS)"]; |
| bsc_mgcp abox bsc_mgcp [label="ST_CRCX (MGCP_MGW_TIMEOUT = 4s)"]; |
| bsc_gscon note bsc_mgcp [label="two timeouts running in parallel"]; |
| bsc_gscon note bsc_mgcp [label="note: #define MGCP_MGW_TIMEOUT exists twice, |
| once in libosmo-mgcp-client, |
| once in bsc_subscr_conn_fsm.c"]; |
| bsc_mgcp -> bsc_gscon [label="mgcp_conn_create() exits"]; |
| bsc_gscon -> bsc [label="bssmap_handle_assignm_req() exits"]; |
| ...; |
| --- [label="On Timeout"]; |
| bsc_gscon note bsc_gscon [label="The conn FSM likely timeouts first"]; |
| bsc_gscon => msc_ [label="BSSMAP Assignment Failure"]; |
| bsc_gscon abox bsc_gscon [label="ST_ACTIVE"]; |
| bsc_mgcp note bsc_mgcp [label="The MGCP FSM will timeout right after that, and terminate itself, |
| 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. There is code |
| that would emit a BSSMAP Assignment Failure, but not in |
| ST_ACTIVE"]; |
| --- [label="end: 'On Timeout'"]; |
| ...; |
| |
| bsc_mgcp <= mgw [label="CRCX OK (for BTS)"]; |
| bsc_mgcp box bsc_mgcp [label="libosmo-mgcp-client fsm_crcx_resp_cb()"]; |
| bsc_mgcp -> bsc_gscon [label="GSCON_EV_MGW_CRCX_RESP_BTS"]; |
| --- [label="end: 'is the chan_mode a speech mode?'"]; |
| |
| bsc_gscon note bsc_gscon [label="for mode=sign, we're still handling GSCON_EV_A_ASSIGNMENT_CMD; |
| for speech mode, we're handling GSCON_EV_MGW_CRCX_RESP_BTS"]; |
| bsc <- bsc_gscon [label="gsm0808_assign_req()"]; |
| |
| bsc box bsc [label="lchan_alloc(): pick available lchan"]; |
| bsc box bsc [label="rsl_chan_activate_lchan()"]; |
| |
| --- [label="is the chosen lchan on dynamic timeslot that is currently used as PDCH?"]; |
| bts <= bsc [label="i) RSL RF Chan Release of PDCH (Osmocom dyn TS)"]; |
| bts <= bsc [label="OR ii) RSL PDCH Deact (ip.access dyn TS)"]; |
| bsc -> bsc_gscon [label="gsm0808_assign_req() returns early"]; |
| bsc_gscon abox bsc_gscon [label="ST_WAIT_ASS_COMPL (GSM0808_T10_VALUE=6s)"]; |
| ...; |
| bts note bsc_gscon [linecolor="red", |
| label="Osmocom style dyn TS use lchan->act_timer to watch over RF Chan Release, but there |
| seems to be no timer watching over PDCH Deact!"]; |
| ...; |
| bts => bsc [label="i) RSL RF Chan Release ACK (Osmocom dyn TS)"]; |
| bts => bsc [label="OR ii) RSL PDCH Deact ACK (ip.access dyn TS)"]; |
| bsc box bsc [label="rsl_chan_activate_lchan() re-invoked"]; |
| bsc box bsc [label="lchan->state = LCHAN_S_ACT_REQ"]; |
| bts <= bsc [label="RSL Chan Activ"]; |
| --- [label="else (no dyn TS switchover)"]; |
| |
| bsc box bsc [label="lchan->state = LCHAN_S_ACT_REQ"]; |
| bts <= bsc [label="RSL Chan Activ"]; |
| bsc -> bsc_gscon [label="gsm0808_assign_req() returns"]; |
| bsc_gscon abox bsc_gscon [label="ST_WAIT_ASS_COMPL (GSM0808_T10_VALUE=6s)"]; |
| ---; |
| |
| ...; |
| --- [label="On Timeout"]; |
| bsc_gscon => msc_ [label="BSSMAP Assignment Failure"]; |
| bsc_gscon abox bsc_gscon [label="ST_ACTIVE"]; |
| bsc_gscon note bsc_mgcp [linecolor="red", |
| label="The mgcp FSM from CRCX above apparently lacks a cleanup action for this case. |
| It should be cleaned up eventually when the conn is torn down, but we should |
| release RTP endpoints as soon as possible."]; |
| --- [label="end: 'On Timeout'"]; |
| ...; |
| |
| bts => bsc [label="RSL Chan Activ ACK"]; |
| bsc box bsc [label="rsl_rx_chan_act_ack()"]; |
| bsc box bsc [label="Stop lchan->act_timer"]; |
| bsc box bsc [label="lchan->state = LCHAN_S_ACTIVE"]; |
| bsc -> bsc [label="S_LCHAN_ACTIVATE_ACK"]; |
| bsc box bsc [label="bsc_api.c handle_chan_ack()"]; |
| ms <= bsc [label="RR Assignment Command"]; |
| |
| ...; |
| ms note bsc_gscon [label="We rely on the overall conn FSM ST_WAIT_ASS_COMPL timeout."]; |
| ...; |
| |
| ms => bsc [label="RR Assignment Complete"]; |
| bsc box bsc [label="handle_ass_compl()"]; |
| --- [label="Release old lchan"]; |
| bsc box bsc [label="_lchan_handle_release(sacch_deact=0)"]; |
| bsc box bsc [label="rsl_release_sapis_from(start=1)"]; |
| bts <= bsc [label="RSL Release Request (Local End)..."]; |
| bts <= bsc [label="...for each SAPI except link_id=0"]; |
| bsc box bsc [label="rsl_release_request(link_id=0)"]; |
| bts <= bsc [label="RSL Release Request (Local End) for link_id=0"]; |
| bsc box bsc [label="_lchan_handle_release() returns here, the remaining release is asynchronous; |
| see `End: 'Release old lchan'` below."]; |
| ...; |
| bts note bsc_gscon [linecolor="red", |
| label="There seems to be no timer watching over RSL Release Request!"]; |
| ...; |
| bts => bsc [label="RSL Release Confirm..."]; |
| bts => bsc [label="...for each SAPI and link_id=0"]; |
| bsc abox bsc [label="start T3111"]; |
| ...; |
| bsc box bsc [label="T3111 expires"]; |
| bsc abox bsc [label="Start lchan->act_timer with lchan_deact_tmr_cb"]; |
| bts <= bsc [label="RSL RF Channel Release"]; |
| ...; |
| --- [label="On timeout"]; |
| bsc box bsc [label="lchan_deact_tmr_cb()"]; |
| bsc box bsc [label="rsl_lchan_mark_broken(): state=LCHAN_S_BROKEN"]; |
| bsc box bsc [label="lchan_free()"]; |
| bsc -> bsc [label="S_LCHAN_UNEXPECTED_RELEASE"]; |
| bsc box bsc [label="bsc_api.c handle_release()"]; |
| bsc box bsc [label="bsc->assign_fail()"]; |
| bsc -> bsc_gscon [label="GSCON_EV_RR_ASS_FAIL"]; |
| bsc note bsc_gscon [linecolor="orange", |
| label="The name 'RR_ASS_FAIL' might suggest the event means an actual RR Assignment |
| Failure message being received. Maybe this should be called GSCON_EV_ASSIGNMENT_ERROR."]; |
| ...; |
| bsc box bsc [label="bsc->clear_request()"]; |
| bsc box bsc [label="bsc_clear_request encodes a BSSMAP Clear Request message and passes it on |
| to the conn FSM as data argument via:"]; |
| bsc -> bsc_gscon [label="GSCON_EV_TX_SCCP"]; |
| bsc_gscon => msc_ [label="BSSMAP Clear Request"]; |
| bsc note bsc_gscon [linecolor="red", |
| label="Instead of sending an arbitrary message, the conn FSM should |
| be explicitly instructed to clear the connection, to be able |
| to notice if the MSC failed to respond to the Clear Request. |
| Currently, this relies on the MSC responding with a Clear |
| Command, hopefully, some time later."]; |
| --- [label="End: 'On timeout'"]; |
| ...; |
| bts => bsc [label="RSL RF Channel Release Ack"]; |
| bsc box bsc [label="Stop lchan->act_timer"]; |
| bsc box bsc [label="Stop lchan->T3111"]; |
| --- [label="End: 'Release old lchan'"]; |
| bsc box bsc [label="still in handle_ass_compl()"]; |
| bsc note bsc [label="officially take over new lchan: conn->lchan = conn->secondary_lchan"]; |
| --- [label="is BTS using IPA Abis? (osmo-bts, ip.access)"]; |
| bts <= bsc [label="IPACC CRCX"]; |
| ---; |
| bsc -> bsc [label="handle_ass_compl() calls bsc_api->assign_compl()"]; |
| --- [label="is BTS using IPA Abis? (osmo-bts, ip.access) && conn->user_plane.rtp_ip"]; |
| bsc box bsc [label="bsc_assign_compl()"]; |
| bsc note bsc [label="set ass_compl.valid = true, |
| postponing GSCON_EV_RR_ASS_COMPL until after the |
| IPACC MDCX ACK received in osmo_bsc_audio.c"]; |
| bsc box bsc [label="exit early: bsc_assign_compl()"]; |
| bsc box bsc [label="exit early: handle_ass_compl()"]; |
| bsc box bsc [label="osmo_bsc_audio.c"]; |
| bts => bsc [label="IPACC CRCX ACK"]; |
| bts <= bsc [label="IPACC MDCX"]; |
| bts => bsc [label="IPACC MDCX ACK"]; |
| bsc box bsc [label="handle_abisip_signal()"]; |
| bsc -> bsc_gscon [label="GSCON_EV_RR_ASS_COMPL"]; |
| --- [label="else"]; |
| bsc box bsc [label="bsc_assign_compl()"]; |
| bsc -> bsc_gscon [label="GSCON_EV_RR_ASS_COMPL"]; |
| --- ; |
| |
| --- [label="is 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 => mgw [label="MDCX (for BTS)"]; |
| bsc_mgcp <= mgw [label="MDCX OK"]; |
| 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 [label="CRCX (for MSC)"]; |
| bsc_mgcp <= mgw [label="CRCX OK (for MSC)"]; |
| bsc_gscon <- bsc_mgcp [label="GSCON_EV_MGW_CRCX_RESP_MSC"]; |
| ---; |
| |
| bsc_gscon => msc_ [label="BSSMAP Assignment Complete"]; |
| |
| bsc_gscon abox bsc_gscon [label="ST_ACTIVE"]; |
| } |