diff options
Diffstat (limited to 'manuals/OsmoNITB/chapters/bsc.adoc')
-rw-r--r-- | manuals/OsmoNITB/chapters/bsc.adoc | 120 |
1 files changed, 120 insertions, 0 deletions
diff --git a/manuals/OsmoNITB/chapters/bsc.adoc b/manuals/OsmoNITB/chapters/bsc.adoc new file mode 100644 index 000000000..49d25e5a9 --- /dev/null +++ b/manuals/OsmoNITB/chapters/bsc.adoc @@ -0,0 +1,120 @@ +== BSC level configuration + +The BSC component is shared between OsmoBSC and OsmoNITB. This chapter +describes some of the configuration options related to this shared BSC +component. + +=== Hand-over + +==== Hand-over in GSM + +Hand-over is the process of changing a MS with a currently active +dedicated channel from one BTS to another BTS. As opposed to idle mode, +where the MS autonomously performs cell re-selection, in dedicated mode +this happens under network control. + +In order to determine when to perform hand-over, and to which cells, the +network requests the MS to perform measurements on a list of neighbor +cell channels, which the MS then reports back to the network in the form +of GSM RR 'Measurement Result' messages. Those messages contain the +downlink measurements as determined by the MS. + +Furthermore, the BTS also performs measurements on the uplink, and +communicates those by means of RSL to the BSC. + +The hand-over decision is made by an algorithm that processes those +measurement results and determines when to perform the hand-over. + +==== Configuration of hand-over in OsmoBSC/OsmoNITB + +OsmoBSC (like the internal BSC component of OsmoNITB) only support +so-called intra-BSC hand-over, where the hand-over is performed between +two BTSs within the same BSC. + +Hand-over is enabled and configured by the use of a set of `handover` +commands. Using those, you can tune the key parameters of the hand-over +algorithm and adapt it to your specific environment. + +.Example handover configuration snippet +---- + handover 1 <1> + handover window rxlev averaging 10 <2> + handover window rxqual averaging 1 <3> + handover window rxlev neighbor averaging 10 <4> + handover power budget interval 6 <5> + handover power budget hysteresis 3 <6> + handover maximum distance 9999 <7> +---- +<1> Enable hand-over +<2> Set the RxLev averaging window for the serving cell to 10 measurements +<3> Set the RxQual averaging window for the serving cell to 1 + measurement (no window) +<4> Set the RxLev averaging for neighbor cells to 10 measurements +<5> Check for the conditions of a power budget hand-over every 6 SACCH + frames +<6> A neighbor cell must be at least 3 dB stronger than the serving cell + to be considered a candidate for hand-over +<7> Perform a maximum distance hand-over if TA is larger 9999 (i.e. never) + +//TODO: Move all to BSC node + +=== Timer Configuration + +The GSM specification specifies a variety of timers both on the network +as well as on the mobile station side. + +Those timers can be configured using the `timer tXXXX` command. + +.Configurable Timers +|=== +|node|timer|default|description +|network|t3101|10|Timeout for 'Immediate Assignment' (sec) +|network|t3103|?|Timeout for Handover (sec) +|network|t3105|40|Repetition of 'Physical Information' (sec) +|network|t3107|?|? +|network|t3109|?|RSL SACCH deactivation timeout (sec) +|network|t3111|?|RSL timeout to wait before releasing the RF channel (sec) +|network|t3113|60|Time to try paging for a subscriber (sec) +|network|t3115|?|? +|network|t3117|?|? +|network|t3119|?|? +|network|t3122|10|Waiting time after 'Immediate Assignment Reject' +|network|t3141|?|? +|=== + +//TODO: split between BSC and MSC timers + +=== Discontinuous Transmission (DTX) + +GSM provides a full-duplex voice call service. However, in any +civilized communication between human beings, only one of the +participants is speaking at any given point in time. This means that +most of the time, one of the two directions of the radio link is +transmitting so-called 'silence frames'. + +During such periods of quiescence in one of the two directions, it is +possible to suppress transmission of most of the radio bursts, as there +is no voice signal to transport. GSM calls this feature 'Discontinuous +Transmission'. It exists separately for uplink (DTXu) and downlink +(DTXd). + +Downlink DTX is only permitted on non-primary transceivers (!= TRX0), as +TRX0 must always transmit at constant output power to ensure it is +detected during cell selection. + +Uplink DTX is possible on any TRX, and serves primarily two uses: + +possible on any TRX, and serves primarily two uses: + +. reducing the MS battery consumption by transmitting at a lower duty cycle +. reducing the uplink interference caused in surrounding cells that + re-use the same ARFCN. + +DTS for both uplink and downlink is implemented in the BTS. Not all BTS +models support it. + +The Osmocom BSC component can instruct the BTS to enable or disable +uplink and/or downlink DTX by means of A-bis OML. + +//TODO: Test/implement, at least for uplink +//TODO: Move to BSC |