I'm curious, why is there a dropdown in the Security section that allows you to set the type of encryption? Did Motorola forget to remove this if programming a repeater or does it restrict the repeater to a certain type of encryption?
The DMR standard is sorely lacking when it comes to encryption. As far as I can tell, to this day, the PI Header frame contents aren't even defined in the standard. No provision was made for late entry encryption data, which is why algorithms that require that data (EP, AES) are forced to steal bits from voice frames in order to transmit the next superframe's MI value. That still leaves the key ID which also has to be sent in order for radios to join/decrypt an active EP/AES call. If radios miss the call setup, specifically the PI Header frame, say due to a noise burst, they have no key ID data to facilitate selecting the correct EP/AES key from their key tables and the radios are forced to remain muted.
When the repeater's encryption type is set to EP, the repeater steals more bits in order to continuously send the key ID data, which lets late entering radios acquire all of the information they need to join/decrypt the call in progress.
Meanwhile, P25 sends all of this encryption data (AlgID, KeyID, 64 bit MI) in every LDU2 frame, making late entry a breeze. DMR is saddled with ghetto 32 bit MIs because stealing 144 voice bits (64 MI bits, 8 CRC bits, 72 FEC bits) from every 360 ms superframe is out of the question, so 32 bit MIs it is. No doubt, these DMR limitations and the required hackery / bit stealing exists because Motorola really wanted to cripple DMR, especially in the encryption 'nads. Typical corporate douchebaggery.
I remember 5 or 6 years ago, it was tried right in front of me, and the Enc. from the portables wouldn't pass through the repeater.
