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diff --git a/doc/old/assignment.msc b/doc/old/assignment.msc
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+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"];
+}