[TrunkCom] partial encryption and if so how is this possible?

[Mike Vander Veer]

OK, I'll try to explain this one...

On conventional Encrypted P25, the Pro-96 will NOT skip the transmission
On trunked Encrypted P25 with a 3600bps control channel, the Pro-96 WILL 
skip the transmission*
On trunked Encrypted P25 with a 9066bps control channel, the Pro-96 WILL NOT 
skip the transmission.

On 3600bps control channels, as long as the first user to transmit is 
encrypted, you won't hear it since the control channel carries the encrypted 
status bit throughout the conversation.  If the first person to transmit is 
not encrypted, they you will hear it and any encrypted transmissions that 
follow until the repeater times out and a new one is used.

On 9600bps control channels, the only message that carries the encryption 
flag is the initial channel grant. The update messages do not, which makes 
it difficult if not impossible for the scanner manufactures to determine 
encryption until they switch to the voice channel.

Mike




----- Original Message ----- 
From: "JERRY NONE" <thepolishdude at yahoo.com>
To: "Discussion of Monitoring Trunk Radio Systems" 
<trunkcom at mailman.qth.net>
Sent: Friday, January 07, 2005 9:55 AM
Subject: RE: [TrunkCom] partial encryption and if so how is this possible?


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> Somebody correct me if I am wrong but on the Pro-96,
> the radio scanner will skip right on over ENCRYPTED
> transmissions but UNENCRYPTED transmissions will stop
> it while in scan mode.
> --- Gary Hahn <garyhahn at wi.rr.com> wrote:
>
>> Win a new Icom IC-756PROIII and help QSL/QTH.net
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>> It's actually quite common, even on encrypted analog
>> channels.  The
>> receiving end will receive whether it's encrypted or
>> not...the radio figures
>> it out. (not unlike the BC796D figuring out if a
>> transmission is P25 or
>> analog)  So if I have mine set to encrypt and you do
>> not, we can still hold
>> a conversation.  I think both the transmitting and
>> receiving parties
>> typically have indicators on the radio telling them
>> whether encryption is
>> being used or not, since I've heard receiving
>> parties warn transmitting
>> parties that they're in the clear.
>>
>> >
>> >
>> > Good morning to all on the list.  I have noticed
>> that when
>> > listening to conversations on Michigan.s digital
>> 800 MHz
>> > system (MPSCS) there have been times where
>> conversations are
>> > partially encrypted.  This morning I heard what
>> sounded like
>> > some kind of road commission or something, but one
>> side of
>> > the conversation was clear and the other was
>> encrypted.  I.ve
>> > never known any system to do this, and the person
>> who was
>> > clear wasn.t asking the person who was encrypted
>> for a
>> > retransmit or anything.  As I said I only got to
>> listen to
>> > this for a few minutes and couldn.t guess on what
>> the agency
>> > was, but I found this to be strange.
>> >
>> >
>>
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