bts-examples: add example for E1 connected BTS

The manual lacks an example on how to set up an E1 connected BTS.
Especially the relation between trunk number and E1 line number is not
obvious.

Change-Id: I02f5d4fe059e5cc9c3ffc2e3636d812532c09239
Related: OS#5308
This commit is contained in:
Philipp Maier 2021-11-25 15:40:10 +01:00
parent 67fb8b7c17
commit 5cebdefed6
1 changed files with 117 additions and 0 deletions

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@ -174,3 +174,120 @@ network
For building a multi-TRX setup, you also need to connect the TIB cables
between the two nanoBTS units, as well as the coaxial/RF AUX cabling.
====
=== Example configuration for OsmoBSC with E1 BTS
The following configuration sample illustrates the usage of BTSs that are
connected via an E1/T1 backhaul.
.OsmoBSC configured for single-TRX E1 Ericsson DUG20
====
----
e1_input <1>
e1_line 0 driver dahdi
e1_line 0 port 3
network
network country code 1
mobile network code 1
encryption a5 0
neci 1
handover 0
bts 0
type rbs2000
band GSM900
om2000 version-limit oml gen 12 rev 10 <2>
cell_identity 0
location_area_code 1
training_sequence_code 7
base_station_id_code 63
ms max power 15
cell reselection hysteresis 4
rxlev access min 0
channel allocator ascending
rach tx integer 9
rach max transmission 7
oml e1 line 0 timeslot 1 sub-slot full <3>
oml e1 tei 62 <4>
gprs mode none
is-connection-list add 4 512 12 <5>
is-connection-list add 16 524 12
is-connection-list add 28 536 12
is-connection-list add 40 548 12
trx 0
rf_locked 0
arfcn 123
nominal power 42
max_power_red 12
rsl e1 line 0 timeslot 1 sub-slot full <6>
rsl e1 tei 0 <7>
timeslot 0
phys_chan_config CCCH+SDCCH4
hopping enabled 0
e1 line 0 timeslot 1 sub-slot full <8>
timeslot 1
phys_chan_config TCH/F
hopping enabled 0
e1 line 0 timeslot 2 sub-slot 1 <9>
timeslot 2
phys_chan_config TCH/F
hopping enabled 0
e1 line 0 timeslot 2 sub-slot 2
timeslot 3
phys_chan_config TCH/F
hopping enabled 0
e1 line 0 timeslot 2 sub-slot 3
timeslot 4
phys_chan_config TCH/F
hopping enabled 0
e1 line 0 timeslot 3 sub-slot 0
timeslot 5
phys_chan_config TCH/F
hopping enabled 0
e1 line 0 timeslot 3 sub-slot 1
timeslot 6
phys_chan_config TCH/F
hopping enabled 0
e1 line 0 timeslot 3 sub-slot 2
timeslot 7
phys_chan_config TCH/F
hopping enabled 0
e1 line 0 timeslot 3 sub-slot 3
----
====
<1> In this example we use a dahdi E1 card. This card has 4 ports. Here we use port numer 3. It should be noted that the dahdi driver also requires additional configuration, which is not covered by this manual.
<2> In this example we use an E1 Ericsson DUG20, which uses an OML dialect, called "OM2000".
<3> The first usable timeslot on an E1 line is TS1. In this example we will assume that TS1-TS3 are connected to the BTS stright through. TS1 will handle all signaling traffic. Here we assign this timeslot to OML.
<4> OML always requires a TEI (Terminal Equipment Identifier) to set up. This number can be found in the manual of the BTS.
<5> This BTS has an built in “Interface Switch” (IS) that offers flexible way to reconfigure the interconnection between the internal components of the BTS and the external E1 line. This depends on the exact BTS type and configuration.
<6> Similar to OML we assign TS1 to RSL as well.
<7> Like with OML, RSL also requires a TEI to be configured. Usually each TRX will have a specific TEI assigned.
<8> CCCH+SDCCH4 will also be mapped on TS1. The traffic for those control channels will be multiplexed alongside the RSL and OML traffic.
<9> The bandwidth of one E1 timeslot matches the bandwidth of 4 GSM air interface timeslots. The E1 timeslot is split up into four sub-slots, which are then assigned to one GSM air interface timeslot each. Since the first timeslot on the first TRX is already used for signaling we begin the sub-slot counting with sub-slot 1 for alignment reasons.
=== E1 Line number and MGCP trunk number
The switching of the voice channels is done via OsmoMGW, which acts as a media
converter between E1 and VoIP (RTP). OsmoBSC will use the E1 line number to
address the trunk via MGCP.
When configuring OsmoMGW, one needs to make sure that the trunk number that is
set up on OsmoMGW, matches the line number that is set up on OsmoBSC. When those
numbers mismatch the trunk cannot be addressed correctly.
.OsmoMGW trunk configuration that matches the OsmoBSC configuration above
====
----
trunk 0
rtp keep-alive once
no rtp keep-alive
line 0
----
====