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Bug #4036

fn-advance and rts-advance seem to do the same thing?

Added by laforge 3 months ago. Updated 3 months ago.

Status:
Resolved
Priority:
Normal
Assignee:
Category:
osmo-bts-trx
Target version:
-
Start date:
06/02/2019
Due date:
% Done:

100%

Spec Reference:

Description

There are two osmo-bts-trx specific settings: fn-advance and rts-advance.

  • they seem to do exactly the same thing: Advance the frame number in order to compensate for delays between osmo-trx and osmo-bts-trx
  • they seem to be used both only in scheduler_trx.c:trx_sched_fn() within very few lines from each other
  • they are simply added together.

In the default configuration, there's 20 frames of fn-advance and 5 frames of rts-advance, accounting for a total advance of 25 frames (of 4.616ms each, totalling to 115.4ms).

The documentation also seems wrong, as it claims rts-advance is specific to the PCU while fn-advance is generic. However, I cannot see any difference between those two. Am I missing something?

History

#1 Updated by laforge 3 months ago

  • Status changed from New to In Progress
  • % Done changed from 0 to 80

As sylvain points out, only fn-advance is used when pulling bursts out of the bottom of the osmo-bts scheduler. The sum of fn-advance and rts-advance is used when pulling MAC blocks out of Layer2 (LAPDm, RTP, PCUIF).

I've updated the related documentation in https://gerrit.osmocom.org/c/osmo-bts/+/14334

#2 Updated by laforge 3 months ago

  • Status changed from In Progress to Resolved
  • % Done changed from 80 to 100

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