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pespin gerrit-no-reply at lists.osmocom.orgpespin has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-pcu/+/22531 ) Change subject: doc: Introduce section documenting NACC support ...................................................................... doc: Introduce section documenting NACC support Change-Id: I74e4828ed1b99a7f4d28ea4797c93ee85c0068cb --- M doc/manuals/chapters/configuration.adoc 1 file changed, 80 insertions(+), 0 deletions(-) git pull ssh://gerrit.osmocom.org:29418/osmo-pcu refs/changes/31/22531/1 diff --git a/doc/manuals/chapters/configuration.adoc b/doc/manuals/chapters/configuration.adoc index f3323d7..7371e72 100644 --- a/doc/manuals/chapters/configuration.adoc +++ b/doc/manuals/chapters/configuration.adoc @@ -220,6 +220,86 @@ Set the gamma parameter for MS power control in units of dB. +=== Configuring Network Assisted Cell Change (NACC) + +Network Assisted Cell Change, defined in 3GPP TS 44.060 sub-clause 8.8, is a +feature providing the MS aid when changing to a new cell due to autonomous +reselection. In summary, the MS informs the current cell its intention to change +to a new target cell, and the network decides whether to grant the intended cell +change or order a change to another neighbor cell. It also provides several +System Informations of the target cell to the MS to allow for quicker +reselection towards it. + +OsmoPCU will automatically provide the required neighbor System Information when +the MS requests NACC towards a target cell also under the management of the same +OsmoPCU instance, since it already has the System Information of all BTS under +their control, obtained through PCUIF when the BTS registers against OsmoPCU, so +no specific user configuration is required here. + +However, for remote neighbors (cells managed by another OsmoPCU instance), +OsmoPCU requires to gather the information from somewhere else before being able +to provide it to the MS requesting the NACC. + +If OsmoPCU fails to gather the System Information, it will simply answer the MS +allowing the proposed changed but without previously providing the System +Information of the target cell. + +==== Neighbor Address Resolution + +First of all, it needs to translate the <ARFCN + BSIC> identity of the target +cell to change to, provided by the MS, into an identity that the Core Network +can use and understand to identify the target cell, which happens to be a key +composed of <RAI + Cell Identity>. This key is also named conveniently as +CGI-PS, since it actually equals to the Circuit Switch CGI + RAC. + +In order to apply this target cell identity translation, OsmoPCU uses the +OsmoBSC Neighbor Resolution CTRL interface (see OsmoBSC User Manual), since the +BSC is the node holding all the neighbor related information. +By default, the use of this interface is not configured and hence disabled in +OsmoPCU. As a result, until configured, the network won't be able to provide the +System Information to the MS prior to allowing the change during NACC against +remote cells, which means the cell change will take longer to complete. In order +to configure the interface, the OsmoBSC IP address and port to connect to must +be configured in OsmoPCU VTY. + +These neighbor address resolutions (<ARFCN + BSIC> => <RAI + CI>) are by default +cached for a while in order to avoid querying the BSC frequently and, as a +result, optimizing the resolution time too. + +.Example: Configure Neighbor Resolution CTRL interface against OsmoBSC +---- +pcu + neighbor resolution 172.18.13.10 4248 <1> + timer X1 500 <2> + timer X0 60 <3> +---- +<1> Port 4248 is the default and hence could be omitted in this case +<2> Time out if the BSC doesn't answer our CTRL resolution request after 500 ms +<3> Keep resolved neighbor addresses cached for 60 seconds + +==== System Information Resolution + +Once OsmoPCU gains knowledge of the target cell's address in the Core Network, +it can query its System Information. The query is done using RIM procedures +(NACC RAN-INFO application) over the Gb interface against the SGSN that OsmoPCU +is connected to. In its turn, the SGSN will potentially forward this query to +the PCU serving the target cell, which will provide back the System Information +of that cell. + +The System Information received from remote neighbors are by default +cached for a while in order to avoid querying the SGSN frequently and, as a +result, optimizing the resolution time too. + +.Example: Configure System Information resolution +---- +pcu + timer X2 500 <1> + timer X11 60 <2> +---- +<1> Time out if the SGSN doesn't answer our RIM RAN-INFO request request after 500 ms +<2> Keep resolved remote neighbor System Information cached for 60 seconds + + === GPRS vs EGPRS considerations ==== Configuration -- To view, visit https://gerrit.osmocom.org/c/osmo-pcu/+/22531 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: osmo-pcu Gerrit-Branch: master Gerrit-Change-Id: I74e4828ed1b99a7f4d28ea4797c93ee85c0068cb Gerrit-Change-Number: 22531 Gerrit-PatchSet: 1 Gerrit-Owner: pespin <pespin at sysmocom.de> Gerrit-MessageType: newchange -------------- next part -------------- An HTML attachment was scrubbed... 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