Cellular Network Infrastructure » cni-legacy » OpenBSC

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== Configuring OpenBSC with muiltiple BTS and in-call handover ==

=== Prerequisites ===

It is assumed that you already have a functioning [wiki:osmo-nitb OpenBSC NITB] and two or more BTS available.

Note that if you are using BTS based on OsmoBTS/OsmoTRX handover requires:

* osmo-bts package version >= fw-5 (this [http://cgit.osmocom.org/osmo-bts/commit/?h=fairwaves/master&id=a6ad0b44ae45a2fd51b6a55507e8295605431e92 fix] is included)

* osmo-trx package version >= 0.2.0 (this [http://cgit.osmocom.org/osmo-trx/commit/?h=fairwaves/master&id=19c392df82fe7acd303e4340059c87c432623881 patch] is included)

=== Example network architecture ===

In this example we have one system running the NITB software and two BTS that are built on the [wiki:OsmoBTS] software.

{{{

#!graphviz

digraph G {

  rankdir = LR;

  BSC -> BTS0 [ label = "A-bis" dir=both ];

  BSC -> BTS1 [ label = "A-bis" dir=both ];

  BSC [ shape = square label = "BSC\n172.30.1.10" ];

  BTS0 [ shape = square label = "BTS 0\n172.30.1.11" ];

  BTS1 [ shape = square label = "BTS 1\n172.30.1.12" ];

  }

}}}

=== BTS configuration ===

There are three OsmoBTS parameters in particular which must be correctly configured:

* '''band''' - the band in which the BTS will operate

* '''ipa unit-id''' - each BTS must use a unique value

* '''oml remote-ip''' - this is the BSC IP address

The example configuration that follows is for two BTS both on the GSM900 band.

==== BTS 0 ====

Find the aforementioned parameters and ensure that they are correctly set.

{{{

bts 0

 band GSM900

 ipa unit-id 1801 0

 oml remote-ip 172.30.1.10

 ...

}}}

==== BTS 1 ====

Ensure that the second BTS has a different '''ipa unit-id''' configured from the first.

{{{

bts 1

 band GSM900

 ipa unit-id 1802 0

 oml remote-ip 172.30.1.10

 ...

}}}

=== BSC configuration ===

There are a number of OpenBSC NITB parameters that you must pay particular attention to:

* '''BTS ''n'''

   * '''band''' - as configured in the BTS

   * '''base_station_id_code''' - should be unique in location area

   * '''ip.access unit_id''' - as configured in the BTS

   * '''trx ''n''

      * '''arfcn''' - this must be frequencies that you have a licence for and the 

* '''neighbor-list mode automatic'''

Configure the first BTS within OpenBSC NITB:

{{{

bts 0

  ...

  band GSM900

  ...

  base_station_id_code 63

  ...

  ip.access unit_id 1801 0

  ...

  neighbor-list mode automatic

  ...

  trx 0

   rf_locked 0

   arfcn 74

   ...

  trx 1

   rf_locked 0

   arfcn 84

   ...

}}}

Ensuring that you have set the correct '''band''' and '''ip.access unit_id''', and an appropriate '''arfcn''' for each TRX.

Next configure the second BTS:

{{{

bts 1

  ...

  band GSM900

  ...

  base_station_id_code 62

  ...

  ip.access unit_id 1802 0

  ...

  neighbor-list mode automatic

  ...

  trx 0

   rf_locked 0

   arfcn 111

   ...

  trx 1

   rf_locked 0

   arfcn 122

   ...

}}}

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. 

Of course, there are many other core parameters that can be set and which may be important to your installation. For details of all the configuration options please see the [wiki:osmo-nitb_VTY NITB VTY reference].

==== Handover ====

The following parameters must also be configured in order to enable handover:

* '''handover 1'''

   * ''Enable in-call handover between multiple BTS.''

* '''handover window rxlev averaging 10'''

   * ''The receive level of the serving cell should be averaged over 10 SACCH frames.''

* '''handover window rxqual averaging 1'''

   * ''The receive quality of the serving cell should be averaged over 1 SACCH frame.''

* '''handover window rxlev neighbor averaging 10'''

   * ''The Rx Level of a neighbour cell should be averaged over 10 SACCH frames.''

* '''handover power budget interval 6'''

   * ''Consider performing a power budget (Rx level) handover every 6 SACCH frames.''

* '''handover power budget hysteresis 3'''

   * ''Set hysteresis (prevents continuous handover back and forth) to 3.''

* '''handover maximum distance 9999'''

   * ''When the distance from the BTS is greater than 9999 attempt a distance handover.''

These parameters must be set within the '''network''' section of the OpenBSC NITB configuration: 

{{{

network

 network country code 1

 ...

 handover 1

 handover window rxlev averaging 10

 handover window rxqual averaging 1

 handover window rxlev neighbor averaging 10

 handover power budget interval 6

 handover power budget hysteresis 3

 handover maximum distance 9999

}}}

Values can be tuned to modify the behaviour of handover.

=== Complete configurations ===

Complete example configs are included for reference and should not be used without modification, unless you happen to have a licence for those particular frequencies.

==== BTS 0 ====

{{{

bts 0

 band GSM900

 ipa unit-id 1801 0

 oml remote-ip 172.30.1.10

 rtp jitter-buffer 0

 paging lifetime 0

 gsmtap-sapi bcch

 gsmtap-sapi ccch

 gsmtap-sapi rach

 gsmtap-sapi agch

 gsmtap-sapi pch

 gsmtap-sapi sdcch

 gsmtap-sapi pacch

 gsmtap-sapi pdtch

 gsmtap-sapi sacch

 fn-advance 20

 ms-power-loop -10

 timing-advance-loop

 trx 0

  rxgain 12

  power 0

 trx 1

  rxgain 12

  power 0

}}}

==== BTS 1 ====

{{{

bts 1

 band GSM900

 ipa unit-id 1802 0

 oml remote-ip 172.30.1.10

 rtp jitter-buffer 0

 paging lifetime 0

 gsmtap-sapi bcch

 gsmtap-sapi ccch

 gsmtap-sapi rach

 gsmtap-sapi agch

 gsmtap-sapi pch

 gsmtap-sapi sdcch

 gsmtap-sapi pacch

 gsmtap-sapi pdtch

 gsmtap-sapi sacch

 fn-advance 20

 ms-power-loop -10

 timing-advance-loop

 trx 0

  rxgain 12

  power 0

 trx 1

  rxgain 12

  power 0

}}}

==== OpenBSC NITB ====

{{{

!

! OpenBSC (UNKNOWN) configuration saved from vty

!!

password foo

!

line vty

 no login

!

e1_input

 e1_line 0 driver ipa

 e1_line 0 port 0

 no e1_line 0 keepalive

network

 network country code 1

 mobile network code 1

 short name Osmocom

 long name Osmocom

 auth policy accept-all

 location updating reject cause 13

 encryption a5 0

 neci 1

 paging any use tch 0

 rrlp mode none

 mm info 1

 handover 1

 handover window rxlev averaging 10

 handover window rxqual averaging 1

 handover window rxlev neighbor averaging 10

 handover power budget interval 6

 handover power budget hysteresis 3

 handover maximum distance 9999

 timer t3101 10

 timer t3103 0

 timer t3105 0

 timer t3107 0

 timer t3109 4

 timer t3111 0

 timer t3113 60

 timer t3115 0

 timer t3117 0

 timer t3119 0

 timer t3122 10

 timer t3141 0

 dtx-used 0

 subscriber-keep-in-ram 0

 bts 0

  type sysmobts

  band GSM900

  cell_identity 0

  location_area_code 1

  base_station_id_code 63

  ms max power 15

  cell reselection hysteresis 4

  rxlev access min 0

  periodic location update 30

  radio-link-timeout 32

  channel allocator ascending

  rach tx integer 9

  rach max transmission 7

  channel-descrption attach 1

  channel-descrption bs-pa-mfrms 5

  channel-descrption bs-ag-blks-res 1

  ip.access unit_id 1801 0

  oml ip.access stream_id 255 line 0

  neighbor-list mode automatic

  gprs mode none

  no force-combined-si

  trx 0

   rf_locked 0

   arfcn 74

   nominal power 23

   max_power_red 0

   rsl e1 tei 0

    timeslot 0

     phys_chan_config CCCH+SDCCH4

     hopping enabled 0

    timeslot 1

     phys_chan_config SDCCH8

     hopping enabled 0

    timeslot 2

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 3

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 4

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 5

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 6

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 7

     phys_chan_config TCH/F

     hopping enabled 0

  trx 1

   rf_locked 0

   arfcn 84

   nominal power 23

   max_power_red 0

   rsl e1 tei 0

    timeslot 0

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 1

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 2

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 3

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 4

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 5

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 6

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 7

     phys_chan_config TCH/F

     hopping enabled 0

 bts 1

  type sysmobts

  band GSM900

  cell_identity 0

  location_area_code 1

  base_station_id_code 62

  ms max power 15

  cell reselection hysteresis 4

  rxlev access min 0

  periodic location update 30

  radio-link-timeout 32

  channel allocator ascending

  rach tx integer 9

  rach max transmission 7

  channel-descrption attach 1

  channel-descrption bs-pa-mfrms 5

  channel-descrption bs-ag-blks-res 1

  ip.access unit_id 1802 0

  oml ip.access stream_id 255 line 0

  neighbor-list mode automatic

  gprs mode none

  no force-combined-si

  trx 0

   rf_locked 0

   arfcn 111

   nominal power 23

   max_power_red 0

   rsl e1 tei 0

    timeslot 0

     phys_chan_config CCCH+SDCCH4

     hopping enabled 0

    timeslot 1

     phys_chan_config SDCCH8

     hopping enabled 0

    timeslot 2

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 3

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 4

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 5

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 6

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 7

     phys_chan_config TCH/F

     hopping enabled 0

  trx 1

   rf_locked 0

   arfcn 122

   nominal power 23

   max_power_red 0

   rsl e1 tei 0

    timeslot 0

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 1

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 2

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 3

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 4

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 5

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 6

     phys_chan_config TCH/F

     hopping enabled 0

    timeslot 7

     phys_chan_config TCH/F

     hopping enabled 0

}}}