path: root/doc/assignment-fsm.dot
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authorNeels Hofmeyr <neels@hofmeyr.de>2018-04-11 01:28:21 +0200
committerNeels Hofmeyr <neels@hofmeyr.de>2018-07-16 16:24:58 +0200
commit58a87a55fa2a8c90167e620c351679b4d5bcb63b (patch)
tree2de121d6a2a76cfccc3a1f38517663e4995dd74e /doc/assignment-fsm.dot
parentb0dcf068f4fa784441b18f8fe2c1eca9fb540325 (diff)
prevent ARFCN+BSIC collisions in configneels/inter_bsc_ho_saved2
If multiple BTS are configured with identical ARFCN+BSIC, handover cannot possibly work. Add warn_on_arfcn_bsic_collisions() and when collisions are detected: - exit right away on program startup. - warn on vty bts node-exit (go_parent_cb()), i.e. when ARFCN+BSIC collide implicitly from default values. - warn on vty bts/base_station_id_code cmd coming from telnet vty, i.e. when the user actively configures colliding BSIC. - warn on vty trx/arfcn cmd coming from telnet vty, i.e. when the user actively configures colliding ARFCN. When warning, warn on all of: - DHO log, - stderr, - vty_out() in case a vty instance is passed (i.e. from interactive vty). It's better to log this once too often than let the user miss it. Rationale: when I started to implement ttcn3 tests for inter-bsc HO, I saw that the new code based on ARFCN+BSIC would cause a handover request intended to go from BTS 0 to BTS 1 to instead go from BTS 0 to back to BTS 0 -- because of identical ARFCN+BSIC in the config of ttcn3-bsc-tests. Such a config badly confuses handover: measurement reports interpreted to come from the wrong cell, all handovers attempted to go to the first BTS (sometimes correctly, sometimes wrongly), in short, non-obvious failure across the handover board. The network would appear to work well, but occasionally a handover would kill a call without apparent reason. It seems worthwhile to prevent such misconfiguration as early as possible, and even allow previous ARFCN+BSIC misconfiguration that used to work to instead break now (only upon reading config during program startup, to not cause program exit just because a user introduces a temporary collision in an interactive vty session). Change-Id: Ia7c38188ccbad5d8b7398e3e5220015e62c08c8b
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