Commit Graph

100 Commits

Author SHA1 Message Date
Vadim Yanitskiy 8631189d9e power_control: add CTRL command for sending default params
There exists a VTY command for sending default power control params,
but so far there was no CTRL counterpart for it.  This patch adds a
SET command 'send-power-control-defaults':

  $ osmo_ctrl.py \
	--host 127.0.0.1 -p 4249 \
	--set "bts.0.send-power-control-defaults" 1

Similar to 'send-new-system-informations', this command takes an
arbitrary dummy value (required for SET), which is simply ignored.

Change-Id: Ib370bd97ee2d9f72f8bec553550b1792d1345387
Related: SYS#6138
2022-09-30 01:02:57 +07:00
Pau Espin 3dca75e1e2 doc: Document use of Osmux in IPA Abis against OsmoBTS
Related: SYS#5987
Change-Id: I41788f8d3bc29735cc30516f429311b73ba71910
2022-09-19 08:45:24 +00:00
Pau Espin 57c2e68da2 vty: Allow setting LAC as hexadecimal value
The LAC value currently configured is now printed as hexadecimal value
too.
It can still be entered as a decimal value in order to keep backward
compatibility, though the hexadecimal one is now preferred.

Related: OS#5631
Depends: libosmocore.git Ia2b7fbbf5502c28374c21dbff548232680da27d4
Change-Id: I9090d73ae9d39244b79b9dbafa1b164faebabc52
2022-09-19 08:44:25 +00:00
Vadim Yanitskiy a019e9af8b lchan_select: implement dynamic selection mode for assignment
This change implements an additional channel allocation mode, which
can be employed during a TCH channel allocation for assignment.
Selection between ascending and descending order is performed
depending on pre-configured parameters:

* Uplink RxLev threshold and number of samples for averaging,
* C0 (BCCH carrier) channel load threshold.

This is useful in setups where Tx power of the RF carriers cannot be
adjusted +dynamically at run-time and thus BS Power Control cannot
be performed.  In such setups the BCCH carrier is transmitting at
relatively higher power than the other RF carriers.  The key idea
is to allocate channels in a smarter way, so that UEs with poor signal
would get channels on carriers with high Tx power, while UEs with good
signal could use carriers with lower Tx power.

Change-Id: I1b7a0d706976b73cc5c30a8714b830811addfe8d
Related: osmo-ttcn3-hacks.git Ia522f37c1c001b3a36f5145b8875fbb88311c2e5
Related: SYS#5460
2022-06-30 16:36:55 +00:00
Vadim Yanitskiy c2928ac269 lchan_select: allow different alloc order for assignment and handover
A follow-up patch implements a special channel allocation mode, which is
only working for assignment (basically TCH selection for a voice call).
This mode cannot be employed for initial CHANNEL REQUEST or handover due
to the absence of an already established lchan.

Adding this mode to the existing VTY command syntax would be confusing:

  channel allocator (ascending|desscending|dynamic)
                                           ^^^^^^^

so this patch extends the VTY syntax in a way that it becomes possible
to configure different channel allocator modes for different cases:

  OsmoBSC(config-net-bts)# channel allocator mode ?
    set-all     Set a single mode for all variants
    chan-req    Channel allocation for CHANNEL REQUEST (RACH)
    assignment  Channel allocation for assignment
    handover    Channel allocation for handover

The old command syntax, which is basically 'set-all', is kept for
backwards compatibility, but marked as deprecated.

Change-Id: I3ae73b36ee9433cc768376b56f0765e5f416162f
Related: SYS#5460
2022-06-30 16:36:41 +00:00
Vadim Yanitskiy ff9d3a64dc lchan_select: prepare a list of timeslots once, iterate over it
The lchan_avail_by_type() attempts to find an unused lchan for the
given GSM_LCHAN_* value: TCH/F, TCH/H, or SDCCH.  This is achieved
by looking up timeslots with compatible GSM_PCHAN_* values.

For instance, finding an unused SDCCH lchan may involve:

* attempt to find a timeslot with pchan=GSM_PCHAN_CCCH_SDCCH4,
* attempt to find a timeslot with pchan=GSM_PCHAN_CCCH_SDCCH4_CBCH,
* attempt to find a timeslot with pchan=GSM_PCHAN_SDCCH8_SACCH8C,
* attempt to find a timeslot with pchan=GSM_PCHAN_SDCCH8_SACCH8C_CBCH,
* attempt to find a timeslot with pchan=GSM_PCHAN_OSMO_DYN (switched),
* attempt to find a timeslot with pchan=GSM_PCHAN_OSMO_DYN (not switched).

Each attempt involves iterating over all timeslots of each TRX,
either in ascending or in descending order (see _lc_dyn_find_bts()
and _lc_find_trx()).

This patch simplifies the lookup logic by preparing a monolithic
array of timeslot pointers once, and then using that array for
each GSM_PCHAN_* lookup attempt.  This change is required for the
upcoming dynamic channel allocation mode, which is fa more complex
than the existing ascending/descending ones.

A side effect of this change is that the interference aware mode
of allocation is not limited by the scope of a single TRX anymore.
Interference levels are now compared within the scope of the whole
BTS, so that lchans on the other TRXes may be picked if they are
better according to the interference reports from the BTS.

Change-Id: I7ccc56856bfd40fd7c63b7437736de60c2b516ff
Related: SYS#5460
2022-06-30 16:36:41 +00:00
Vadim Yanitskiy b06fc25539 doc/manuals: document channel allocation parameters
Change-Id: Ib77eb3d4ad896f1e37b52e549ca3c24f4980240b
Related: SYS#5460
2022-06-23 05:48:04 +07:00
Pau Espin beed1365fa doc: bsc.adoc: Update timer info from code (gsm_network_T_defs)
Change-Id: I1652e6d53f568f606b692b16d4198d5209df2d9c
2022-03-02 17:34:43 +01:00
Philipp Maier 5cebdefed6 bts-examples: add example for E1 connected BTS
The manual lacks an example on how to set up an E1 connected BTS.
Especially the relation between trunk number and E1 line number is not
obvious.

Change-Id: I02f5d4fe059e5cc9c3ffc2e3636d812532c09239
Related: OS#5308
2021-12-06 19:03:37 +01:00
Vadim Yanitskiy c122c10f34 [overpower] By default, permit only for speech channels using AMR
Change-Id: I087025f9db59348f2f70d4a291f8d887644d6b17
Related: SYS#5319
2021-11-15 11:59:03 +00:00
Vadim Yanitskiy 335361fbeb [overpower] Allow configuring specific channel mode(s)
Change-Id: I34d29d7d0f66c629367f3d6e8a660e199ecbe080
Related: SYS#5319
2021-11-15 11:59:03 +00:00
Vadim Yanitskiy fa3c917bb1 doc/manuals: fix wrong CI in the inter-BSC handover diagram
The 'bts0' in BSS 'Beta' has LAC=42/CI=3.  There is no LAC=42/CI=6.

Change-Id: I0f2e351e802311d4601579c2e755ca13a9056348
2021-11-14 19:35:00 +03:00
Vadim Yanitskiy a507875ae7 doc/manuals: add documentation for Temporary ACCH Overpower
Change-Id: Ie995dac6c7083a2b0b4d582f71f55b3736381edb
Related: SYS#5319
2021-11-12 22:52:02 +03:00
Vadim Yanitskiy 5944ff07a8 gsm_data: use ascending order for interference boundaries
It's more logical to have the boundaries sorted in ascending order:

  * band 1 represents lowest interference levels,
  * band 5 represents highest interference levels.

Change-Id: Ie9bf4bf0c89418685b8ea5096332d22cfba7c521
Related: SYS#5313
2021-11-10 14:45:12 +03:00
Vadim Yanitskiy dd0dabbffc doc/manuals: add documentation for interference reporting
Change-Id: I3c15b11bbcba0811e3a15fe64365067bf8ad0dae
Related: SYS#5313
2021-11-10 14:42:17 +03:00
Philipp Maier 9cb639daad control.adoc: comment out fixme note
The fixme note:
"FIXME: add variables defined in src/ctrl/control_if.c?"

is not directed at the reader of the manual. It should stay in the
source, but it should not be visible in the pdf. Lets comment it out.

Change-Id: Id68f53d18f0873af3c07a0ae52cd12bc94bc0b96
2021-11-03 17:25:28 +00:00
Philipp Maier 3ca2ae1d0a bsc_ctrl_commands: change neighbor-list mode/arfcn via control interface
It is possible to change the neighbor-list mode via the VTY from
automatic mode to manual neighbor-list configuration. In the manual
mode, the user can add ARFCN values manually. This command can be found
under the bts node. Lets add pendant of this command on the control
interface as well.

Change-Id: Id97bc0d31a358db6221c385761773fb48670c921
Related: SYS#5641
2021-11-03 17:25:28 +00:00
Philipp Maier 085a92584f heighbor_ident: add/del neighbor cells via ctrl interface
The VTY allows flexible control over the neighbor cell information via
the neighbor command, which can be found in the configure terminal under
the bts node. Lets add pendant of this command on the control interface
as well.

Change-Id: I343a40e18fa9b91e6c381912c0426a002841e079
Related: SYS#5641
2021-11-03 17:25:28 +00:00
Philipp Maier 554e169784 control.adoc: improve description of command bts.N.send-new-system-informations
Change-Id: I48bdb7fd991dac2d5112440c879d0ded5b726715
Related: SYS#5641
2021-11-02 10:52:51 +00:00
Pau Espin d203d173f2 MS Power Control Loop: Use P_CON_INTERVAL=2 by default
Increase the reaction time at the expense of more stable loop with less
temporary oscillations.

See updated user manual documentation in this commit for a larger
description.

Related: SYS#5371
Change-Id: I46be244a5e01a74086e3a977ec3ea139742a0074
2021-10-07 10:44:44 +00:00
Pau Espin 464227d071 MS Power Control Loop: Allow Turn off/on C/I independent from value setting
Improve the current VTY support to allow enabling/disabling C/I logic
independent from value setting. This way C/I support can be quickly
disabled & enabled.

Reminder: changing power parameters still require VTY Command "bts NR
resend-power-control-defaults" to be excuted prior to new parameters
being applied on the BTS.

Related: SYS#4917
Change-Id: Id1224c2d9a52db2ed805c49e048d3086ed0167f5
2021-09-29 15:39:17 +02:00
Pau Espin df612507d6 MS Power Control Loop: Support turn off C/I based logic
Setting LOWER_CMP_N and UPPER_CMP_N for all channel types can be quite
cumbersome and end up in lengthy config files. Let's instead add a
placeholder command to apply it to all channel types of a BTS at once.
This is useful specially since a user disabling C/I capabilities
probably does so because it may require a fair amount of fine-tuning
parameters to have it working perfectly. Hence, a user not willing to
spend time configuring those parameters correctly (and for which default
ones doesn't work properly) will require quick way to get rid of C/I
based MS Power Control Loop. By disabling C/I comparison, osmo-bts will
rely on RxLev only when applying the MS Power Control Loop, which is
fine for non noisy environments.

Related: SYS#4917
Change-Id: I0e1a1a9228a15e9ec9c41b7952b03e1d25309706
2021-09-21 16:51:21 +02:00
Philipp Maier 12a73bd3c3 doc/mgwpool: update documentation
The mgw-pool now allows to set a decription for each MGW /MGCP client
instance. Update the documentation so that it reflects the current
state.

Change-Id: I3026e027bba1a9a12ceca64e96df993b5957cb1d
Related: SYS#5091
2021-09-15 10:04:47 +00:00
Pau Espin 8367411772 Power Control Loop: Set P_CON_INTERVAL to 1 by default
TS 45.008 section 4.7.1:
"""
Upon receipt of a command from an SACCH to change its power level on the corresponding uplink channel, the MS
shall change to the new level at a rate of one nominal 2 dB power control step every 60 ms (13 TDMA frames), i.e. a
range change of 15 steps should take about 900 ms. The change shall commence at the first TDMA frame belonging to
the next reporting period (as specified in subclause 8.4). The MS shall change the power one nominal 2 dB step at a
time, at a rate of one step every 60 ms following the initial change, irrespective of whether actual transmission takes
place or not.
"""

Since the reported MS_PWR in L1 SACCH Header is, according to specs, the
one used for the last block of the previous SACCH period, it becomes
clear the first SACCH block after a requested MS Power Level change by
the network may contain mismatches between the announced MS_PWR by the
MS and the measured Rxlev/RxQual. Hence, let's better use a
P_CON_INTERVAL of 1 which retriggers the MS Power Control Loop every second
SACCH block.

Related: SYS#5371
Change-Id: Iade5b597e0e56b07c6d78995fcec7c641e4e643f
2021-09-13 17:48:48 +02:00
Pau Espin 506aa70d77 Support Neighbor Address Resolution over PCUIF IPA multiplex
While NACC was initially developed, it became clear there was need for
a way to interact PCU<->BSC in order resolve ARFCN+BSIC into CGI-PS
for later RIM usage.
Hence, this resolution was first (until today) implemented using an out
of bands RPC system using the CTRL interface, which required specific
config to be written and matches in osmo-pcu and osmo-bsc VTY (ip+port
of the CTRL interface to use).
However, this has several shortcomings:
* As explained above, specific configuration is required
* Since recently, we do support BSC redundancy in osmo-bts. Hence the BTS
  may switch to a BSC other than first one. If that happened, that'd mean
  the CTRL interface would still point to the initially configured one,
  which may not be the same currently serving the PCU.

During recent development of ANR related features, a similar need for
PCU<->BSC was required, but this time it was decided to extend the IPA
multiplex of the Abis OML connection to pass PCUIF messages,
transparently forwarded to each side by the BTS.
This has the advantage that connection PCU<->BTS is handled by BTS and
both sides send messages transparently.

Let's switch by default to using this new interface, while still
maintaing the old way for a while (announcing them as deprecated) to
avoid breaking existing deployments until they are upgraded to new
versions of osmo-pcu and osmo-bsc.

Change-Id: I9073a121564503f483c84263ac72476041e47c03
Related: SYS#4971
2021-09-13 16:04:05 +02:00
Pau Espin 87aa619d0b doc: power_control.adoc: Add small time graph showcasing P_CON_INTERVAL
Original graph made by Vadim Yanitskiy.

Change-Id: I9b76088b2d46973b477deb555214d64fcc746754
Related: SYS#5371
2021-09-06 12:26:59 +02:00
Pau Espin 54283ba626 MS Power Control Loop: Support set up of C/I parameters for osmo-bts
This commit extends existing VTY and RSL infrastructure to configure and
manage MS Power Parameters used in MS Power Control loop, by adding
support to set up Carrier-to-Interference (CI) parameters.

Using C/I instead of existing RxQual is preferred due to extended
granularity of C/I (bigger range than RxQual's 0-7).
Furthermore, existing literature (such as "GSM/EDGE: Evolution and Performance"
Table 10.3) provides detailed information about expected target values,
even different values for different channel types. Hence, it was decided
to support setting different MS Power Parameters for different channel
types.

These MS Power Parameters are Osmocom specific, ie. supported only by
newish versions of osmo-bts. Older versions of osmo-bts should ignore
the new IEs added just fine. The new IEs containing the MS POwer
Parameters are not send for non osmo-bts BTSs, hence this commit is
secure with regards to running  osmo-bsc against an ip.access BTS such
as nanoBTS.

Related: SYS#4917
Depends: libosmocore.git Change-Id Iffef0611430ad6c90606149c398d80158633bbca
Change-Id: I7e76ec47b323d469f777624b74b08752d1f5584f
2021-09-06 12:07:20 +02:00
Pau Espin da06d183e7 doc: power_control.adoc: Improve VTY snippet foot notes
Change-Id: Ie5f129c418c187d4f331d6e92884f4f507fb018f
2021-09-06 12:07:20 +02:00
Philipp Maier 8d22e68706 osmo_bsc_main: integrate MGW pooling into osmo-bsc
Since the libosmo-mgcp-client now supports MGW pooling, lets use this
feature in osmo-bsc. Large RAN installations may benefit from
distributing the RTP voice stream load on multiple media gateways.

Depends: osmo-mgw Icaaba0e470e916eefddfee750b83f5f65291a6b0
Change-Id: I8f33ab2cea04b545c403a6fe479aa963a0fc0d0d
Related: SYS#5091
2021-09-03 15:03:38 +00:00
Pau Espin 0f34f7e72f doc: manual: Fix typo in text
Change-Id: I1dfe298ad9a416ea15976527463a55873db56f22
2021-08-26 13:19:30 +02:00
Pau Espin 694d43f706 doc: Improve ACC ramp documentation
Commit below added support for ACC ramping based on channel load, but
documentation was not updated with it.

Fixes: 1e5e7004dc
Change-Id: I8701386b35ccdebfc843fd00535091648e52f739
2021-08-19 14:50:02 +00:00
Philipp Maier c96c05f07b osmo_bsc_main: remove unused commandline option -l
The option -l ("The local address of the MGCP") is still present in the
commandline help and the manual, but it is used nowhere and osmo-bsc
exists when it is used. Lets remove it.

Change-Id: Ia295f4414e0d6e78b388c0c72f1a5b8df8bc3d7e
2021-08-03 12:11:32 +02:00
Philipp Maier a23c7be0a1 running.adoc: explain mgw reset-endpoint VTY setting
When OsmoBSC is restarted, it does not automatically clear the calls on
the MGW. However, this is an important part of the configuration to
avoid trouble with resource leakage on the MGW, so lets make (especially
novice) users aware of that option.

Change-Id: I19c499c6ac83d7f9437b18b372977f6f2d518adf
Depends: osmo-mgw I47e7ff858d5067b46d52329be5f362ff61c0dff8
Related: SYS#5535
2021-08-03 11:44:57 +02:00
Philipp Maier 181b5f3b9a handover_ctrl: add control interface for handover settings
The VTY handover_vtc.c offers a large number of handover specific
settings. Those settings are (with one exception) auto generated using
macros. Lets add an equivalent for the control interface that uses the
same auto generation mechanisms.

Change-Id: I12f143906818fd6b16e8783157cbb1eb51e49ffc
Depends: libosmocore I53fc207677f52b1dc748b01d58424839cdba807c
Related: SYS#5369
2021-07-19 10:44:05 +02:00
Pau Espin fd3204e0de doc: bts.adoc: Update dyn ts section to include SDCCH8 support
Related: SYS#5309
Change-Id: I40f4b19e7df83351c9c9e65d71880ac6aaa4ee88
2021-07-09 10:45:04 +02:00
Pau Espin cc75145131 Rename osmo dyn ts enums to contain SDCCH8
They will gain support to be activated as SDCCH/8 soon too.

Related: OS#5309
Depends: libosmocore.git I56dcfe4d17899630b17f80145c3ced72f1e91e68
Change-Id: Id5b89fe589a52ff88486435ac43809edb4b80f98
2021-07-06 07:16:15 +00:00
Vadim Yanitskiy 997a257f8d power_control: constrain BS power reduction on BCCH carrier
BS Power Control is not allowed on the BCCH/CCCH carrier, unless
the BTS is operating in the BCCH carrier power reduction mode.

Allow constrained BS power reduction (up to 6 dB) on active logical
channels iff BCCH carrier power reduction mode is enabled.

Take into account that the maximum power difference between a timeslot
used for BCCH/CCCH and the timeslot preceding it shall not exceed 3 dB.

Change-Id: I2cc6a86731984f586ef35b43a8d3de631f7d8a2f
Related: SYS#4919, SYS#4918
2021-07-05 12:17:59 +00:00
Vadim Yanitskiy ced29cf94c power_control: implement BCCH carrier power reduction operation
The BCCH carrier (sometimes called C0) of a BTS shall maintain
discontinuous Downlink transmission at full power in order to
stay 'visible' to the mobile stations.  Because of that, early
versions of 3GPP TS 45.008 prohibited BS power reduction on C0.

However, starting from version 13.0.0 (2015-11) there is a feature
called 'BCCH carrier power reduction operation'.  This is a special
mode of operation, where the variation of RF level for some
timeslots is relaxed for the purpose of energy saving.

In BCCH carrier power reduction operation, for timeslots on the
C0 carrier, except timeslots carrying BCCH/CCCH, the output power
may be lower than the output power used for timeslots carrying
BCCH/CCCH.  In this case the maximum allowed difference in output
power actually transmitted by the BTS is 6 dB.

Introduce a VTY command to turn on and off the BCCH carrier power
reduction operation.  Also introduce a CTRL command.  On the
A-bis/RSL, abuse the BS POWER CONTROL message by setting
the Channel Number IE to 0x80 (RSL_CHAN_BCCH).

Currently, only osmo-bts-trx is supported.  A value greater than
zero makes it reduce the power on *inactive* timeslots of the
BCCH carrier.  Sending zero disables the BCCH power reduction
mode completely.

For more details, see 3GPP TS 45.008, section 7.1, and 3GPP TR 45.926.

Change-Id: I047fce33d4d3e4c569dd006ba17858467a2f4783
Related: SYS#4919
2021-07-05 12:17:59 +00:00
Philipp Maier 78ad200cf6 control.adoc: add doc for apply-config-file
apply-config-file is not documented in the manual.

Change-Id: I469e3925c1079e45eea246e599bcd50ba3fc9dd3
Related: SYS#5369
2021-06-24 10:15:49 +02:00
Philipp Maier b9930bdf09 bsc_ctrl_commands: add command to write vty config
we recently added control commands to apply vty config files during
runtime using the control interface. However, there is no command that
allows us to store the config file modifications.

Change-Id: If17095bb86f82dd8feb86eb72c4133ea3aa1c3b3
Related: SYS#5369
2021-06-24 10:15:49 +02:00
Philipp Maier 85e660b370 bts.adoc: fix typo BGSGP -> BSSGP
Change-Id: I4387b516c5c116cd7179611dc34a90b0a744cb6c
2021-05-21 10:10:06 +00:00
Harald Welte 858401b04e manual: Include QoS chapter and add osmo-bsc specific example
Change-Id: I3b1d44fc545725172142b903190a3ff5094805dd
Requires: osmo-gsm-manuals.git Id344c29eda2a9b3e36376302b425e9db1f6c0f28
Requires: libosmo-abis.git I8991dd6eb406a5b9a70498974fc1ad339452f871
2021-05-01 17:36:09 +00:00
Neels Hofmeyr aa01d326ff manual: Location Services: clarify BSC side address
A clarification that I promised a while back but forgot to submit.

Related: SYS#4876
Change-Id: I9b06ac7a2f2cb34cabfcec10af761322b8e962fb
2021-04-27 13:39:01 +00:00
Vadim Yanitskiy 3fd19268ae vty: deprecate BTS type 'sysmobts' in favor of 'osmo-bts'
Change-Id: I60d5ff887a7c830180088904c2458f7e73ce3893
2021-04-12 18:54:40 +00:00
Harald Welte f5d0733e44 CBSP: document rate counters and their mapping to basic/extended CBCH
Change-Id: Id298d547a90bb5d8e40f2cd300b7e1303bb43fdc
2021-02-22 13:44:32 +00:00
Philipp Maier ff5dcf7fd3 bts.adoc: describe ACCH repetition settings
The manual currently does not mention ACCH repetition yet. Lets
add some info on how to set up ACCH repetition correctly.

Change-Id: I1e27ac955882497bbeefac0c830708dd18ad46b3
Related: SYS#5114
2021-02-11 23:16:50 +01:00
Vadim Yanitskiy ea8d6939e6 power_control: make P_CON_INTERVAL parameter configurable
Change-Id: I6e0fae81cc60f708e49d5eb8dfc0bbcad926b18f
Related: SYS#4918
2021-02-07 19:20:12 +01:00
Vadim Yanitskiy e1d2691e69 power_control: enable Uplink DPC by default if format is known
So far osmo-bsc would enable Uplink DPC (Dynamic Power Control) only
for osmo-bts, and the 'static' mode for all other BTS models.  This
decision dates back to the time when ip.access specific encoding for
dynamic power control parameters was not implemented, and the MS
Power Parameters IE was sent empty in the RSL messages.

Let's make a step forward by enabling Uplink DPC by default for
all BTS models which declare the API for vendor-specific encoding
of the power control parameters.  Currently this includes osmo-bts
and nanoBTS, both supporting ip.access specific format.

Change-Id: If86d27d4332af3d82f862737340d061e42e34eba
Related: SYS#4918
2021-02-07 04:38:15 +01:00
Pau Espin f93f1dfec2 cosmetic: doc: wrap line too long
Change-Id: I2da6f58d84521289f86840b1da191a9faf76a1a8
2021-01-29 16:01:23 +01:00
Neels Hofmeyr 8e830dd136 hodec2: to balance congestion, use overload percent
For balancing load across congested cells and across congested TCH/*
kinds, instead of comparing the number of lchans above the configured
congestion threshold, compare the percent of lchans of overload.

In short, using a percentage prevents cells with less min-free-slots to
fill up 100% while neighbor cells still may have several free lchans
available.

An obvious example of why this is desirable is illustrated by
test_balance_congestion_by_percentage.ho_vty:

Cell A has min-free-slots 2, and has all slots occupied.
Cell B has min-free-slots 4, and has 2 slots remaining free.

If we count congested lchans as in current master: cell A has a
congestion count of 2: two more lchans in use than "allowed". If we move
one lchan over to cell B, it ends up with a congestion count of 3, which
is worse than 2. So when counting lchans, we decide that cell A should
remain full.

Instead, when comparing percentage of remaining lchans, we would see
that cell A is loaded 100% above congestion (2 of 2 remaining lchans in
use), but when moving one lchan to cell B, that would only be 75% loaded
above its treshold (3 of 4 remaining lchans in use). So a percentage
comparison would cause a handover to cell B.

Related: SYS#5259
Change-Id: I55234c6c99eb02ceee52be0d7388bea14304930f
2021-01-14 06:24:57 +00:00