Author Topic: band indicator = 1800 even though frequency set to 900  (Read 93 times)


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band indicator = 1800 even though frequency set to 900
« on: March 29, 2019, 11:59:51 AM »
I'm having a problem with the phone connecting to the cell station. I have set the BladeRF station to broadcast on the 900MHz range and verified this with another SDR. My cellphone sees the station but can't connect.

Attempted to connect to station then inspected for rejected IMSI numbers. none found.

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nipc list rejected
IMSI            No attempts register
--------------- ---------------

Here is my configuration from ybts.conf

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Here is the wired part. I performed a pcap for GMS traffic. I only see downlink traffic no uplink traffic. In the downlink traffic I see the band indicator field says 1800 even though I have set this to 900MHz. Please see attached pcap.

no. 425 > GSM CCCH > SI 6 Rest Octets > Band Indicator = 1800

I remember seeing a bug that was posted a few years ago about the wrong frequency being broadcast. I'm not sure if this is related.

Is this expected? It would of course help if I got a working pcap as well. I would like to review a pcap on a working configuration.

Here are the commands to get a pcap.

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telnet localhost 5038
mbts config Control.GSMTAP.GSM on
connect phone
Code: [Select]
sudo tcpdump -i any udp port 4729 -w GSMtraffic.pcap