Hi,
I would like to know what are the capabilities of the silent-call implemented in OpenBSC. When I try the command from VTY, I do not get any useful information from the target. Should it be like a normal call where I can listen to the called number but without having the target notified?
Best regards, Robert,
Hi.
No, the silent call has nothing to do with audio - getting access to target's mic without it noticing is not part of GSM spec so in order to implement it you've got to exploit some bug in phone's baseband. I think it's being done couple of times successfully.
Silent call in OpenBSC is about initiating "pre-call" signaling so phone "wakes up", allocates the channel to BTS and waits for further instructions. Normally, the instructions to start ringing, display caller number etc would follow but not in this case. This is perfectly within GSM spec. The point is to get low-level connection to the phone so, for example, it's current position could be requested over RRLP. Or to test smth.
Out of curiosity - what kind of information would you find useful in this case?
On 03/11/2016 03:05 PM, robert wrote:
Hi,
I would like to know what are the capabilities of the silent-call implemented in OpenBSC. When I try the command from VTY, I do not get any useful information from the target. Should it be like a normal call where I can listen to the called number but without having the target notified?
Best regards, Robert,
Hi Robert,
On Fri, Mar 11, 2016 at 04:05:15PM +0200, robert wrote:
I would like to know what are the capabilities of the silent-call implemented in OpenBSC. When I try the command from VTY, I do not get any useful information from the target. Should it be like a normal call where I can listen to the called number but without having the target notified?
a silent call is a pure signalling connection, it does not have any actual voice data. It serves primarily the purpose of turning the MS into a permanently (on one TS) transmitting beacon that can be localized using various radio-localization techniques.
We implemented the feature in order to demonstrate/show-case some of the GSM "mis-features" that are being abused by signalling intelligence / law enforcement devices.
Hi,
Thank you for this explanation.
Best regards, Robert,
On Mar 11, 2016, at 5:04 PM, Harald Welte laforge@gnumonks.org wrote:
Hi Robert,
On Fri, Mar 11, 2016 at 04:05:15PM +0200, robert wrote:
I would like to know what are the capabilities of the silent-call implemented in OpenBSC. When I try the command from VTY, I do not get any useful information from the target. Should it be like a normal call where I can listen to the called number but without having the target notified?
a silent call is a pure signalling connection, it does not have any actual voice data. It serves primarily the purpose of turning the MS into a permanently (on one TS) transmitting beacon that can be localized using various radio-localization techniques.
We implemented the feature in order to demonstrate/show-case some of the GSM "mis-features" that are being abused by signalling intelligence / law enforcement devices. --
- Harald Welte laforge@gnumonks.org http://laforge.gnumonks.org/
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