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path: root/doc/old/lchan-release.msc
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msc {
	hscale=2;
	ms [label="MS"], bts [label="BTS"], bsc[label="BSC"], bsc_gscon[label="BSC conn FSM"];

	ms note bsc_gscon [label="various lchan release scenarios"];
	

	ms rbox bsc_gscon [label="IF BSC releases, from BSSMAP Clear Request"];
	bsc note bsc [label="lchan_release() may be called with sacch_deact=true or false.
		Currently, the only time lchan_release(sacch_deact=true) is invoked is upon BSSMAP Clear
		Command, i.e. when the MSC instructs to stop using an active lchan.
		Some error handling code paths however directly invoke
		rsl_rf_chan_release(error=1, SACCH_DEACTIVATE)."];

	---;
	bsc_gscon note bsc_gscon [label="Rx: BSSMAP Clear Request from MSC"];
	bsc <- bsc_gscon [label="gsm0808_clear()"];
	bsc box bsc [label="lchan_release(sacch_deact=1)"];
	bsc box bsc [label="lchan->state = LCHAN_S_REL_REQ"];
	bsc box bsc [label="_lchan_handle_release(sacch_deact=1)"];
	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"];
	ms <= bsc [label="RR Channel Release"];
	ms note bsc [label="There is no ACK for RR Channel Release"];
	bsc box bsc [label="rsl_deact_sacch()"];
	bts <= bsc [label="RSL Deactivate SACCH"];
	bsc abox bsc [label="Start T3109 (net->T3109, t3109_expired())"];
	...;
	--- [label="If T3109 expires"];
	bsc box bsc [label="t3109_expired()"];
	bsc box bsc [label="rsl_rf_chan_release(error=1)"];
	bts <= bsc [label="RSL Release Request (Local End)..."];
	bts <= bsc [label="...for each SAPI, except link_id=0"];
	bsc box bsc [label="lchan->state = LCHAN_S_REL_REQ"];
	bts <= bsc [label="RSL RF Channel Release"];
	---;
	...;
	bsc rbox bsc [label="continue in the 'Common' part"];
	--- [label="END: 'BSSMAP Clear Request'"];
	...;
	...;

	ms rbox bsc_gscon [label="IF BSC releases, from implicitly unused lchan"];
	bsc note bsc [label="The BSC may release old unused lchans after Handover, or release lchans
		after some error condition."];
	bsc note bsc [label="BSC decides to release an unused lchan"];
	bsc box bsc [label="lchan_release(sacch_deact=0)"];
	bsc box bsc [label="lchan->state = LCHAN_S_REL_REQ"];
	bsc box bsc [label="_lchan_handle_release(sacch_deact=0)"];
	bts <= bsc [label="RSL Release Request (Local End)..."];
	bts <= bsc [label="...for all SAPIs"];
	...;
	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 all SAPIs"];
	bsc rbox bsc [label="continue in the 'Common' part"];
	---;
	...;
	...;

	ms rbox bsc_gscon [label="IF MS releases"];
	ms => bts [label="DISC"];
	bts => bsc [label="RLL Release Ind..."];
	bts => bsc [label="...for each SAPI"];
	bsc rbox bsc [label="continue in the 'Common' part"];
	---;
	...;
	...;
	ms rbox bsc_gscon [label="Common"];
	--- [label="for each SAPI (?)"];
	bts => bsc [label="RLL Release Confirm / RLL Release Ind"];
	bsc box bsc [label="abis_rsl_rx_rll()"];
	bsc box bsc [label="mark lchan->sapis[link_id] = LCHAN_SAPI_UNUSED"];
	bsc box bsc [label="rll_indication()"];
	bsc box bsc [label="for each bsc_rll_req matching this link_id:
		disable timer, call cb(BSC_RLLR_IND_REL_IND)"];
	bsc box bsc [label="rsl_handle_release()"];
	--- [label="IF all SAPIs are unused"];
	bsc box bsc [label="Stop T3109"];
	bsc note bsc [label="T3109 was started if the MSC requested the release"];
	bsc abox bsc [label="Start T3111 (net->T3111 value, t3111_expired())"];
	--- [label="END: all SAPIs are unused"];
	bsc -> bsc_gscon [label="GSCON_EV_RLL_REL_IND (only if RLL Release Ind)"];
	--- [label="END: for each SAPI"];

	...;
	bsc box bsc [label="T3111 expires"];
	bsc box bsc [label="rsl_rf_chan_release()"];
	bsc box bsc [label="Stop T3109"];
	bsc note bsc [label="[If lchan->state is LCHAN_S_REL_ERR, don't do anything]"];
	bsc abox bsc [label="Start lchan->act_timer (4s, lchan_deact_tmr_cb())"];
	bts <= bsc [label="RSL RF Channel Release"];

	...;
	--- [label="IF lchan->act_timer expires"];
	bsc box bsc [label="lchan_deact_tmr_cb()"];
	bsc box bsc [label="rsl_lchan_mark_broken(): lchan->state = LCHAN_S_BROKEN"];
	bsc box bsc [label="lchan_free() (see below)"];
	--- [label="END: 'lchan->act_timer expires'"];
	...;

	bts => bsc [label="RSL RF Channel Release ACK"];
	bsc box bsc [label="rsl_rx_rf_chan_rel_ack()"];
	bsc box bsc [label="Stop lchan->act_timer"];
	bsc box bsc [label="Stop T3111"];

	--- [label="IF lchan->state == LCHAN_S_BROKEN"];
	bsc note bsc [label="If an ACK comes in late, for specific BTS models, we may choose to 'repair'
		the lchan so that it is usable again, by calling do_lchan_free() directly (see below)."];
	bsc box bsc [label="rsl_rx_rf_chan_rel_ack() exits here and none of below actions happen.
		The lchan remains LCHAN_S_BROKEN indefinitely."];
	--- [label="END: lchan->state == LCHAN_S_BROKEN"];
	bsc box bsc [label="do_lchan_free()"];
	--- [label="IF lchan->state == LCHAN_S_REL_ERR"];
	bsc note bsc [label="If release failed, we take the lchan back into operation after due
		timeout"];
	bsc abox bsc [label="Start lchan->error_timer (T3111+2, error_timeout_cb())"];
	bsc note bsc [label="do_lchan_free() continues, async:"];
	...;
	bsc box bsc [label="error_timeout_cb()"];
	bsc box bsc [label="lchan->state = LCHAN_S_NONE"];
	bsc box bsc [label="dyn TS: activate PDCH..."];
	--- [label="ELSE"];
	bsc box bsc [label="lchan->state = LCHAN_S_NONE"];
	--- [label="END: lchan->state == LCHAN_S_REL_ERR"];
	bsc box bsc [label="lchan_free()"];
	--- [label="IF conn is still associated (and not dyn TS in switchover)"];
	bsc -> bsc [label="S_LCHAN_UNEXPECTED_RELEASE"];
	bsc box bsc [label="handle_release()"];
	bsc box bsc [label="Stop T10"];
	bsc note bsc [linecolor=orange,label="conn->T10 is actually dead code, it is never started.
		Instead, the conn FSM starts ST_WAIT_ASS_COMPL with a T10 value."];
	bsc -> bsc_gscon [label="GSCON_EV_RR_ASS_FAIL"];
	bsc -> bsc_gscon [label="GSCON_EV_TX_SCCP: BSSMAP Clear Request"];
	bsc box bsc [label="bsc_clear_handover()"];
	bsc box bsc [label="Stop T3103"];
	bsc box bsc [label="free handover struct"];
	bsc box bsc [label="lchan->conn = NULL"];
	--- [label="END: 'conn is still associated'"];
	bsc box bsc [label="Stop T3101"];
	bsc note bsc [label="T3101 is started when sending an RR Immediate Assignment"];
	bsc -> bsc [label="S_CHALLOC_FREED"];
	bsc -> bsc [label="rll_lchan_signal()"];
	bsc box bsc [label="for each bsc_rll_req matching this lchan:
		disable timer, call cb(BSC_RLLR_IND_REL_IND)"];
}