Scan one or all ports, on UDP or all protocols, to see if I'm getting, what I suppose to get

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http://unix.stackexchange.com – I have a GPS localizer (TK102). I've set it up to send responses over GPRS to particular IP and over particular port. I was told that, it uses UDP. It seems that something is being sent (paid transfer registerd on connection list for phone number used by localizer), but it did not reach server (probably). Seems that my listener, run on server, isn't receiving any responses from the localizer. Listener itself is working fine, because I can send UDP packet from any other client and they are being correctly catched up and registered in DB. I tested NetCat and UDP Test Tool on two various ports (HowTos)