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authorNeels Hofmeyr <neels@hofmeyr.de>2018-05-29 02:45:07 +0200
committerHarald Welte <laforge@gnumonks.org>2018-06-08 16:16:42 +0000
commit9d8d0c67314b2e717ef371187d7ab8d371428ae4 (patch)
treed362810261531db369c0ba7e1d914510a229e7bd
parentc8658ac06e97ee9db1f4416e0f8ab15a0f582462 (diff)
doc: add lchan-release.msc
-rw-r--r--doc/Makefile.am1
-rw-r--r--doc/lchan-release.msc149
2 files changed, 150 insertions, 0 deletions
diff --git a/doc/Makefile.am b/doc/Makefile.am
index cc2e277b5..3c8c2e0fa 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -5,6 +5,7 @@ SUBDIRS = \
msc: \
$(builddir)/handover.png \
$(builddir)/assignment.png \
+ $(builddir)/lchan-release.png \
$(NULL)
$(builddir)/%.png: $(srcdir)/%.msc
diff --git a/doc/lchan-release.msc b/doc/lchan-release.msc
new file mode 100644
index 000000000..f75b559c1
--- /dev/null
+++ b/doc/lchan-release.msc
@@ -0,0 +1,149 @@
+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)"];
+}