I've identified 4 carriers in the 400Mhz band, with a clear 4 state constellation. Is there an easy way to verify it is indeed tetra? I'm using grc.
Gr. Sim
On 01-03-11 10:00, Sylvain Munaut wrote:
I've identified 4 carriers in the 400Mhz band, with a clear 4 state constellation. Is there an easy way to verify it is indeed tetra? I'm using grc.
Try to decode them using osmo-tetra ... (see previous annouce and the README to know how to).
Thanks. I'm struggling a bit how to get a GSMTAP dissector in wireshark. I need to recompile wireshark in order to get there, do i?
BTW it looks that idling causes the 4 state diagram, when there is data, it turns into a 8 sided diamond.
Gr. Sim
On 03/01/2011 10:12 AM, Sim IJskes wrote:
Thanks. I'm struggling a bit how to get a GSMTAP dissector in wireshark. I need to recompile wireshark in order to get there, do i?
Yes, you will need to compile one of the 1.5 development versions of wireshark. If you are using Ubuntu there are some PPAs with wireshark 1.5.1.
On 01-03-11 10:20, Holger Hans Peter Freyther wrote:
On 03/01/2011 10:12 AM, Sim IJskes wrote:
Thanks. I'm struggling a bit how to get a GSMTAP dissector in wireshark. I need to recompile wireshark in order to get there, do i?
Yes, you will need to compile one of the 1.5 development versions of wireshark. If you are using Ubuntu there are some PPAs with wireshark 1.5.1.
Thanks. I've found a PPA @ https://launchpad.net/~dreibh/+archive/ppa it has GSMTAP as a protocol.
I still don't have the right architectual image of GSMTAP i think. Do i need to direct wireshark to sniff on the same interface that tetra-rx opens its udp socket on, with a port filter, or is there a pseudo interface that listens for raw packets on the same UDP port?
Gr. Sim
On 03/01/2011 10:44 AM, Sim IJskes wrote:
Thanks. I've found a PPA @ https://launchpad.net/~dreibh/+archive/ppa it has GSMTAP as a protocol.
I still don't have the right architectual image of GSMTAP i think. Do i need to direct wireshark to sniff on the same interface that tetra-rx opens its udp socket on, with a port filter, or is there a pseudo interface that listens for raw packets on the same UDP port?
There is no pseudo interface. The tetra decoding program sends UDP packets to the IANA assigned port for GSMTAP on the specified ip address. E.g we like to use multicast addresses as this avoid seeing ICMP messages as the destination is not reachable.
The easiest would be to use wireshark's pseudo interface to scan every interface and then filter for udp in the trace and select gsmtap in the filterbar of wireshark.
On 01-03-11 10:54, Holger Hans Peter Freyther wrote:
I still don't have the right architectual image of GSMTAP i think. Do i need to direct wireshark to sniff on the same interface that tetra-rx opens its udp socket on, with a port filter, or is there a pseudo interface that listens for raw packets on the same UDP port?
There is no pseudo interface. The tetra decoding program sends UDP packets to the IANA assigned port for GSMTAP on the specified ip address. E.g we like to use multicast addresses as this avoid seeing ICMP messages as the destination is not reachable.
The easiest would be to use wireshark's pseudo interface to scan every interface and then filter for udp in the trace and select gsmtap in the filterbar of wireshark.
Ok. I've straced tetra-rx and it opens on 127.0.0.1. So i wiresharked it on lo with a port filter. That should work. But tetra-rx doesn't do a write on the udp-socket. That could of course mean there is no tetra data in the capture.
I've rebuild the usrp1-tetra_demod.py in the latest grc from git trunk, and the 25Khz lowpass gives me a nasty spike on -22Khz. A 20Khz gives me a much sharper idle constellation. Do you see any problem with 20Khz lowpass?
Gr. Sim
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Holger Hans Peter Freyther -
Sim IJskes -
Sylvain Munaut