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Multi-BTS with handover » History » Version 10

Anonymous, 02/19/2016 10:48 PM

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[[PageOutline]]
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== Configuring OpenBSC with muiltiple BTS and in-call handover ==
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=== Prerequisites ===
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It is assumed that you already have a functioning BSC/NITB, and two or more BTS available.
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Note that if you are using BTS based on OsmoBTS/OsmoTRX handover requires:
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* osmo-bts package version >= fw-5 (this [http://cgit.osmocom.org/osmo-bts/commit/?h=fairwaves/master&id=a6ad0b44ae45a2fd51b6a55507e8295605431e92 fix] is included)
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* osmo-trx package version >= 0.2.0 (this [http://cgit.osmocom.org/osmo-trx/commit/?h=fairwaves/master&id=19c392df82fe7acd303e4340059c87c432623881 patch] is included)
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=== Example network architecture ===
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In this example we have one system running the BSC/NITB software and two BTS that are built on the [wiki:OsmoBTS] software.
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{{{
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#!graphviz
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digraph G {
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  rankdir = LR;
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  BSC -> BTS0 [ label = "A-bis" dir=both ];
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  BSC -> BTS1 [ label = "A-bis" dir=both ];
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  BSC [ shape = square label = "BSC\n172.30.1.10" ];
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  BTS0 [ shape = square label = "BTS 0\n172.30.1.11" ];
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  BTS1 [ shape = square label = "BTS 1\n172.30.1.12" ];
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  }
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}}}
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=== BTS configuration ===
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There are three OsmoBTS parameters in particular which must be correctly configured:
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* '''bts''' - BTS number in a config file, always 0 for a BTS configuration file, 0..n for the NITB configuration file
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* '''band''' - the band in which the BTS will operate
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* '''ipa unit-id''' - each BTS must use a unique value
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* '''oml remote-ip''' - this is the BSC IP address
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The example configuration that follows is for two BTS both on the GSM900 band.
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==== BTS 0 ====
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Find the aforementioned parameters and ensure that they are correctly set.
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{{{
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bts 0
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 band GSM900
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 ipa unit-id 1801 0
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 oml remote-ip 172.30.1.10
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 ...
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}}}
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==== BTS 1 ====
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Ensure that the second BTS has a different '''ipa unit-id''' configured from the first.
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{{{
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bts 0
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 band GSM900
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 ipa unit-id 1802 0
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 oml remote-ip 172.30.1.10
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 ...
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}}}
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=== BSC configuration ===
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There are a number of BSC/NITB parameters that you must pay particular attention to:
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* '''BTS ''n'''
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   * '''band''' - as configured in the BTS
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   * '''base_station_id_code''' - should be unique in location area
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   * '''ip.access unit_id''' - as configured in the BTS
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   * '''trx ''n''
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      * '''arfcn''' - this must be frequencies that you have a licence for and unique across all neighbouring BTS
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* '''neighbor-list mode automatic'''
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Configure the first BTS within the BSC/NITB, ensuring that you have set the correct '''band''' and '''ip.access unit_id''', and an appropriate '''arfcn''' for each TRX.
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{{{
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bts 0
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  ...
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  band GSM900
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  ...
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  base_station_id_code 63
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  ...
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  ip.access unit_id 1801 0
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  ...
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  neighbor-list mode automatic
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  ...
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  trx 0
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   rf_locked 0
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   arfcn 74
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   ...
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  trx 1
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   rf_locked 0
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   arfcn 84
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   ...
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}}}
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Next configure the second BTS, ensuring that a different '''base_station_id_code''' is used this time, once again the correct '''ip.access unit_id''' is set, and an appropriate '''arfcn''' for each TRX:
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{{{
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bts 1
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  ...
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  band GSM900
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  ...
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  base_station_id_code 62
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  ...
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  ip.access unit_id 1802 0
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  ...
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  neighbor-list mode automatic
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  ...
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  trx 0
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   rf_locked 0
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   arfcn 111
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   ...
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  trx 1
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   rf_locked 0
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   arfcn 122
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   ...
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}}}
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For details of all the configuration options please see the [wiki:osmo-nitb_VTY NITB VTY reference].
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==== Handover ====
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The following parameters must also be configured in order to enable handover:
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* '''handover 1'''
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   * ''Enable in-call handover between multiple BTS.''
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* '''handover window rxlev averaging 10'''
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   * ''The receive level of the serving cell should be averaged over 10 SACCH frames.''
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* '''handover window rxqual averaging 1'''
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   * ''The receive quality of the serving cell should be averaged over 1 SACCH frame.''
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* '''handover window rxlev neighbor averaging 10'''
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   * ''The Rx Level of a neighbour cell should be averaged over 10 SACCH frames.''
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* '''handover power budget interval 6'''
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   * ''Consider performing a power budget (Rx level) handover every 6 SACCH frames.''
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* '''handover power budget hysteresis 3'''
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   * ''Set hysteresis (prevents continuous handover back and forth) to 3.''
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* '''handover maximum distance 9999'''
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   * ''When the distance from the BTS is greater than 9999 attempt a distance handover.''
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These parameters must be set within the '''network''' section of the BSC/NITB configuration: 
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{{{
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network
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 network country code 1
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 ...
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 handover 1
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 handover window rxlev averaging 10
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 handover window rxqual averaging 1
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 handover window rxlev neighbor averaging 10
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 handover power budget interval 6
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 handover power budget hysteresis 3
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 handover maximum distance 9999
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}}}
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Values can be tuned to modify the behaviour of handover.
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=== Testing handover ===
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To test handover you have two options:
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1. Physically move a phone to trigger handover decision.
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2. Use "subscriber ID handover BTS_NR" command in the NITB VTY to force handover.
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=== Complete configurations ===
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Complete example configs are included here for reference only and should not be used without modification, unless you happen to have a licence for those particular frequencies.
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==== BTS 0 ====
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{{{
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bts 0
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 band GSM900
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 ipa unit-id 1801 0
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 oml remote-ip 172.30.1.10
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 rtp jitter-buffer 0
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 paging lifetime 0
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 gsmtap-sapi bcch
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 gsmtap-sapi ccch
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 gsmtap-sapi rach
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 gsmtap-sapi agch
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 gsmtap-sapi pch
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 gsmtap-sapi sdcch
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 gsmtap-sapi pacch
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 gsmtap-sapi pdtch
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 gsmtap-sapi sacch
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 fn-advance 20
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 ms-power-loop -10
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 timing-advance-loop
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 trx 0
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  rxgain 12
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  power 0
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 trx 1
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  rxgain 12
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  power 0
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}}}
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==== BTS 1 ====
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{{{
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bts 0
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 band GSM900
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 ipa unit-id 1802 0
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 oml remote-ip 172.30.1.10
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 rtp jitter-buffer 0
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 paging lifetime 0
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 gsmtap-sapi bcch
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 gsmtap-sapi ccch
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 gsmtap-sapi rach
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 gsmtap-sapi agch
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 gsmtap-sapi pch
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 gsmtap-sapi sdcch
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 gsmtap-sapi pacch
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 gsmtap-sapi pdtch
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 gsmtap-sapi sacch
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 fn-advance 20
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 ms-power-loop -10
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 timing-advance-loop
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 trx 0
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  rxgain 12
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  power 0
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 trx 1
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  rxgain 12
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  power 0
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}}}
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==== OpenBSC NITB ====
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Note that whilst this configuration is for NITB operation, the updates describe above could equally be applied to OpenBSC configured in BSC-only mode and with an external MSC etc.
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{{{
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!
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! OpenBSC (UNKNOWN) configuration saved from vty
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!!
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password foo
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!
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line vty
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 no login
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!
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e1_input
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 e1_line 0 driver ipa
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 e1_line 0 port 0
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 no e1_line 0 keepalive
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network
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 network country code 1
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 mobile network code 1
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 short name Osmocom
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 long name Osmocom
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 auth policy accept-all
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 location updating reject cause 13
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 encryption a5 0
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 neci 1
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 paging any use tch 0
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 rrlp mode none
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 mm info 1
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 handover 1
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 handover window rxlev averaging 10
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 handover window rxqual averaging 1
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 handover window rxlev neighbor averaging 10
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 handover power budget interval 6
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 handover power budget hysteresis 3
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 handover maximum distance 9999
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 timer t3101 10
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 timer t3103 0
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 timer t3105 0
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 timer t3107 0
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 timer t3109 4
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 timer t3111 0
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 timer t3113 60
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 timer t3115 0
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 timer t3117 0
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 timer t3119 0
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 timer t3122 10
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 timer t3141 0
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 dtx-used 0
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 subscriber-keep-in-ram 0
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 bts 0
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  type sysmobts
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  band GSM900
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  cell_identity 0
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  location_area_code 1
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  base_station_id_code 63
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  ms max power 15
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  cell reselection hysteresis 4
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  rxlev access min 0
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  periodic location update 30
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  radio-link-timeout 32
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  channel allocator ascending
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  rach tx integer 9
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  rach max transmission 7
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  channel-descrption attach 1
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  channel-descrption bs-pa-mfrms 5
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  channel-descrption bs-ag-blks-res 1
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  ip.access unit_id 1801 0
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  oml ip.access stream_id 255 line 0
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  neighbor-list mode automatic
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  gprs mode none
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  no force-combined-si
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  trx 0
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   rf_locked 0
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   arfcn 74
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   nominal power 23
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   max_power_red 0
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   rsl e1 tei 0
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    timeslot 0
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     phys_chan_config CCCH+SDCCH4
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     hopping enabled 0
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    timeslot 1
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     phys_chan_config SDCCH8
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     hopping enabled 0
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    timeslot 2
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 3
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 4
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 5
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 6
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 7
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     phys_chan_config TCH/F
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     hopping enabled 0
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  trx 1
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   rf_locked 0
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   arfcn 84
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   nominal power 23
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   max_power_red 0
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   rsl e1 tei 0
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    timeslot 0
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 1
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 2
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 3
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 4
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 5
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 6
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 7
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     phys_chan_config TCH/F
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     hopping enabled 0
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 bts 1
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  type sysmobts
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  band GSM900
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  cell_identity 0
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  location_area_code 1
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  base_station_id_code 62
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  ms max power 15
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  cell reselection hysteresis 4
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  rxlev access min 0
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  periodic location update 30
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  radio-link-timeout 32
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  channel allocator ascending
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  rach tx integer 9
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  rach max transmission 7
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  channel-descrption attach 1
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  channel-descrption bs-pa-mfrms 5
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  channel-descrption bs-ag-blks-res 1
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  ip.access unit_id 1802 0
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  oml ip.access stream_id 255 line 0
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  neighbor-list mode automatic
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  gprs mode none
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  no force-combined-si
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  trx 0
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   rf_locked 0
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   arfcn 111
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   nominal power 23
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   max_power_red 0
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   rsl e1 tei 0
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    timeslot 0
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     phys_chan_config CCCH+SDCCH4
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     hopping enabled 0
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    timeslot 1
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     phys_chan_config SDCCH8
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     hopping enabled 0
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    timeslot 2
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 3
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 4
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 5
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 6
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 7
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     phys_chan_config TCH/F
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     hopping enabled 0
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  trx 1
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   rf_locked 0
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   arfcn 122
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   nominal power 23
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   max_power_red 0
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   rsl e1 tei 0
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    timeslot 0
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 1
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 2
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 3
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 4
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 5
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 6
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     phys_chan_config TCH/F
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     hopping enabled 0
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    timeslot 7
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     phys_chan_config TCH/F
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     hopping enabled 0
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}}}
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