Feature #3236

Rx Assignment Failure from BSC does nothing

Added by neels over 2 years ago. Updated over 1 year ago.

Target version:
Start date:
Due date:
% Done:


Spec Reference:


The code actually says:

/* Receive an ASSIGNMENT FAILURE from BSC */
void msc_assign_fail(struct gsm_subscriber_connection *conn,
                     uint8_t cause, uint8_t *rr_cause)
        LOGP(DRR, LOGL_DEBUG, "MSC assign failure (do nothing).\n");

Thus, when the BSC encounters any failure of allocating an lchan and the MSC is told so, osmo-msc still waits it out, which is ridiculous.
(After a considerable timeout, the call fails, so classifying this as a Feature request, not a bug report.)
osmo-msc should instead abort any ongoing call setup and tell both sides that it's over right away.

I noticed this while dyn TS allocation in osmo-bts is buggy: paging and call alerting happily continues despite the first Assignment actually failing.

The way to reproduce exactly what I saw:

  • revert patch Ic06c8f0fe82ae8a06afa5defd93a685010687965 in osmo-bts
  • configure all as TCH/F_TCH/H_PDCH
  • place a voice call and run into chan activ nack

or otherwise cause a chan activ nack to result when trying to allocate a TCH/x for the call from the BTS,
which then propagates as an Assignment Failure towards the MSC (at least since osmo-bsc patch Ib204b4a5272f9b7b60ca5f932cd8a4c857316270)

(at time of writing those patches aren't actually merged yet, but from a future perspective I expect they will be.)

Related issues

Related to OsmoBSC - Bug #3708: osmo-bsc: Wrong handling of PDCH DEACT NACKResolved11/26/2018

Related to OsmoMSC - Feature #1609: Inter-BSC hand-over is missing (MSC side)Resolved11/21/201611/21/2016


#1 Updated by neels over 2 years ago

  • Description updated (diff)

#2 Updated by laforge over 2 years ago

  • Assignee set to stsp

#3 Updated by laforge about 2 years ago

  • Priority changed from Normal to High

#4 Updated by pespin about 2 years ago

  • Related to Bug #3708: osmo-bsc: Wrong handling of PDCH DEACT NACK added

#5 Updated by neels about 2 years ago

  • Assignee changed from stsp to neels

This is likely to get refactored in the course of inter-BSC and inter-MSC handover implementations,
because that will cause quite elaborate changes in how conns are being handled.

#6 Updated by neels about 2 years ago

  • Related to Feature #1609: Inter-BSC hand-over is missing (MSC side) added

#7 Updated by neels over 1 year ago

  • Status changed from New to Resolved
  • % Done changed from 0 to 100

osmo-msc master (refactored) handles Assignment Failure

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