[PATCH] osmo-gsm-manuals[master]: dynamic timeslots: add BSC level config instructions

This is merely a historical archive of years 2008-2021, before the migration to mailman3.

A maintained and still updated list archive can be found at https://lists.osmocom.org/hyperkitty/list/gerrit-log@lists.osmocom.org/.

Neels Hofmeyr gerrit-no-reply at lists.osmocom.org
Thu Dec 1 02:05:02 UTC 2016


Review at  https://gerrit.osmocom.org/1352

dynamic timeslots: add BSC level config instructions

Add high level description on and a config example for dynamic timeslots in a
new chapter featured in the OsmoBSC and OsmoNITB manuals.

>From the OsmoBTS manual's chapter on dynamic timeslots, add references to the
above.

Change-Id: I44ff1e4c2340c65ff23e85408fc6d6a45ea9e046
---
M OsmoBTS/chapters/dynamic-timeslots.adoc
M common/chapters/bts.adoc
2 files changed, 127 insertions(+), 3 deletions(-)


  git pull ssh://gerrit.osmocom.org:29418/osmo-gsm-manuals refs/changes/52/1352/1

diff --git a/OsmoBTS/chapters/dynamic-timeslots.adoc b/OsmoBTS/chapters/dynamic-timeslots.adoc
index 29dff5b..7c43d18 100644
--- a/OsmoBTS/chapters/dynamic-timeslots.adoc
+++ b/OsmoBTS/chapters/dynamic-timeslots.adoc
@@ -7,11 +7,14 @@
 The Abis message handling for dynamic timeslots is independent of the BTS
 model. However, dynamic switchover will only work for BTS models that implement
 the internal API to reconnect a timeslot (_bts_model_ts_disconnect()_ and
-_bts_model_ts_connect()_).  Currently, these BTS models support dynamic
-timeslots:
+_bts_model_ts_connect()_, see also <<osmobts_hardware_support>>).
+
+Currently, these OsmoBTS models support dynamic timeslots:
 
 * _osmo-bts-sysmo_
 * _osmo-bts-litecell15_
 * _osmo-bts-trx_
 
-See also <<osmobts_hardware_support>>.
+Dynamic timeslots are driven by the BSC and need to be configured there. When
+using OsmoBSC or OsmoNITB, see the BTS configuration chapter on dynamic
+timeslots in <<userman-osmobsc>> or <<userman-osmonitb>>, respectively.
diff --git a/common/chapters/bts.adoc b/common/chapters/bts.adoc
index c9fda7f..80c91d6 100644
--- a/common/chapters/bts.adoc
+++ b/common/chapters/bts.adoc
@@ -267,3 +267,124 @@
 
 Configures the various GPRS NS related timers.  Please check the GPRS NS
 specification for the detailed meaning of those timers.
+
+
+=== Dynamic Timeslot Configuration (TCH / PDCH)
+
+A dynamic timeslot is in principle a voice timeslot (TCH) that is used to serve
+GPRS data (PDCH) when no voice call is active on it. This enhances GPRS
+bandwidth while no voice calls are active, which is dynamically scaled down as
+voice calls need to be served. This is a tremendous improvement in service over
+statically assigning a fixed number of timeslots for voice and data.
+
+Dynamic timeslots work both with OsmoNITB as well as with OsmoBSC driven by a
+third-party MSC. The causality is as follows: to establish a voice call, the
+MSC requests a logical channel of a given TCH kind from the BSC. The BSC
+assigns such a channel from a BTS' TRX's timeslot of its choice. The knowledge
+that a given timeslot is dynamic exists only on the BSC level. When the MSC
+asks for a logical channel, the BSC may switch off PDCH on a dynamic timeslot
+and then assign a logical TCH channel on it. Hence, though compatibility with
+the BTS needs to be ensured, any MSC is compatible with dynamic timeslots by
+definition.
+
+OsmoBSC and OsmoNITB support two kinds of dynamic timeslot handling, configured
+via the `network` / `bts` / `trx` / `timeslot` / `phys_chan_config`
+configuration. Not all BTS models support dynamic channels.
+
+[[dyn_ts_compat]]
+.Dynamic timeslot support by various BTS models
+[cols="50%,25%,25%"]
+|===
+|                    |`TCH/F_TCH/H_PDCH` |`TCH/F_PDCH`
+|ip.access nanoBTS   |-                  |supported
+|Ericsson RBS        |supported          |-
+|sysmoBTS using _osmo-bts-sysmo_ |supported |supported
+|various SDR platforms using _osmo-bts-trx_ |supported |supported
+|Nutaq Litecell 1.5 using _osmo-bts-litecell15_ |supported |supported
+|Octasic OctBTS using _osmo-bts-octphy_ | -  | -
+|===
+
+The _OsmoBTS Abis Protocol Specification_ <<osmobts-abis-spec>> describes the
+non-standard RSL messages used for these timeslot kinds.
+
+NOTE: Same as for dedicated PDCH timeslots, you need to enable GPRS and operate
+a PCU, SGSN and GGSN to provide the actual data service.
+
+==== Osmocom Style Dynamic Timeslots (TCH/F_TCH/H_PDCH)
+
+Timeslots of the `TCH/F_TCH/H_PDCH` type dynamically switch between TCH/F,
+TCH/H and PDCH, depending on the channel kind requested by the MSC. The RSL
+messaging for `TCH/F_TCH/H_PDCH` timeslots is compatible with Ericsson RBS.
+
+BTS models supporting this timeslot kind are shown in <<dyn_ts_compat>>.
+
+NOTE: At the time of writing, OsmoNITB disables TCH/F on this timeslot type due
+to transcoding limitations. Operation of OsmoBSC with a third-party MSC is not
+affected by this limitation. See https://osmocom.org/issues/1778.
+
+==== ip.access Style Dynamic Timeslots (TCH/F_PDCH)
+
+Timeslots of the `TCH/F_PDCH` type dynamically switch between TCH/F and PDCH.
+The RSL messaging for `TCH/F_PDCH` timeslots is compatible with ip.access
+nanoBTS.
+
+BTS models supporting this timeslot kind are shown in <<dyn_ts_compat>>.
+
+==== Avoid PDCH Exhaustion
+
+To avoid disrupting GPRS, configure at least one timeslot as dedicated PDCH.
+With only dynamic timeslots, a given number of voice calls would convert all
+timeslots to TCH, and no PDCH timeslots would be left for GPRS service.
+
+==== Dynamic Timeslot Configuration Examples
+
+This is an extract of an _osmo-nitb_ or _openbsc_ config file. A timeslot
+configuration with five Osmocom style dynamic timeslots and one dedicated PDCH
+may look like this:
+
+----
+network
+ bts 0
+  trx 0
+   timeslot 0
+    phys_chan_config CCCH+SDCCH4
+   timeslot 1
+    phys_chan_config SDCCH8
+   timeslot 2
+    phys_chan_config TCH/F_TCH/H_PDCH
+   timeslot 3
+    phys_chan_config TCH/F_TCH/H_PDCH
+   timeslot 4
+    phys_chan_config TCH/F_TCH/H_PDCH
+   timeslot 5
+    phys_chan_config TCH/F_TCH/H_PDCH
+   timeslot 6
+    phys_chan_config TCH/F_TCH/H_PDCH
+   timeslot 7
+    phys_chan_config PDCH
+----
+
+With the ip.access nanoBTS, only `TCH/F_PDCH` dynamic timeslots are supported,
+and hence a nanoBTS configuration may look like this:
+
+----
+network
+ bts 0
+  trx 0
+   timeslot 0
+    phys_chan_config CCCH+SDCCH4
+   timeslot 1
+    phys_chan_config SDCCH8
+   timeslot 2
+    phys_chan_config TCH/F_PDCH
+   timeslot 3
+    phys_chan_config TCH/F_PDCH
+   timeslot 4
+    phys_chan_config TCH/F_PDCH
+   timeslot 5
+    phys_chan_config TCH/F_PDCH
+   timeslot 6
+    phys_chan_config TCH/F_PDCH
+   timeslot 7
+    phys_chan_config PDCH
+----

-- 
To view, visit https://gerrit.osmocom.org/1352
To unsubscribe, visit https://gerrit.osmocom.org/settings

Gerrit-MessageType: newchange
Gerrit-Change-Id: I44ff1e4c2340c65ff23e85408fc6d6a45ea9e046
Gerrit-PatchSet: 1
Gerrit-Project: osmo-gsm-manuals
Gerrit-Branch: master
Gerrit-Owner: Neels Hofmeyr <nhofmeyr at sysmocom.de>



More information about the gerrit-log mailing list