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Neels Hofmeyr gerrit-no-reply at lists.osmocom.orgReview 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>