Understanding RAS Thread

[jcardani]

Hi all,

I would like to start a thread on how RAS works to un-mute the audio of existing 2-way radios. I understand it's in a CRC/check sum/coding scheme is a certain field or fields. Which field affects RAS and how would the Checksum differ from a non-RAS implementation?

Fields that a FEC and/or check sum are performed in DMR:
(taken from the CML CMX7341 PMR/DMR Common Platform Processor chip data sheet)

EMB field
Slot Type
CACH TACT bits
Embedded signalling
Reverse Channel (RC)
Signalling Short LC in CACH
PI Header
Voice LC header
Terminator with LC
CSBK
Idle message
Data header
Rate 1⁄2 data continuation
Rate 1⁄2 last data block
Rate 3⁄4 data continuation
Rate 3⁄4 last data block
Rate 1 non-last data block
Rate 1 last data block
Response header block
Response data block MBC header
MBC continuation MBC last block
UDT header
UDT continuation UDT last block

 

[Forts]

I believe it's in the Voice LC header, but could be in other blocks as well. From my understanding it looks like the RAS key is added to a block of data, which is then CRC'd, then the RAS key is removed and the data and CRC sent over the air. A receiving radio with the proper key will be able to recover the original data and the CRC will pass... all is good. No key = bad CRC = no audio. And to really monkey with things, only a portion of the key is actually used. How it's determined which portion, I don't know...my eyes glazed over when I was looking at the patent info.

 

[jcardani]

Hi Forts,

Happy Thanksgiving. Therefore DSD/DSDPlus then would ignore the CRC check on the LC header correct?

Do you know the patent number that you referenced?

thanks!

 

[Forts]

Correct... DSDPlus doesn't care if the CRC is bad and will happily carry on (actually I believe the messed up CRC is used in recent Fast Lane DSDPlus builds as an indicator that RAS may be in use).

The patent in question is here: https://www.google.com/patents/US20130288643

 

[Forts]

RAS was also discussed in some detail a while ago over at Communications Support: New TRBO security feature: No more passive monitoring

 

[redbeard]

I'm getting an RAS indication in DSD+ but can still listen on my XPR 7550. DSD+ also won't show me the CC channel frequency anymore. I am not positive, but I want to say the control channel sounds a little different than usual now. This all started happening after the site added a new frequency. Any thoughts anyone?

 

[redbeard]

Since I'm not getting any answers, let me expand a bit with details. I'm thinking there might have been a slight change in the over the air protocol for the CON+ control channels. There was a new freq added to the site and that might have been a good opportunity for the tech to upgrade firmware while at the site.

I have two different setups running DSD+. One is running public 1.074 with a tapped 996XT just watching CC data and occasionally decoding some slot 2 audio. Two is running dual RTL-SDR.com sticks, the new version with SMA on the end. I am using fast lane 1.101pt on that machine and 2 instances of both FMP and DSD+ for control channel and voice follow.

Both setups intermittently give me an RAS indication where the color code and neighbor list are shown in the DSD+ event log window. I can however still passively monitor the system on my XPR 7550 by just scanning the freqs and using the RX list to hold talkgroups I want to hear. If RAS was actually implemented my understanding is that I couldn't listen on my XPR anymore.

Also, with the public release I never edited any of the freq, network, or group info. I used to get the channel activity window updated after a little while of monitoring, showing the CC on LCN 1 and then slots 2-6 on the 3 freq site. Now, CC always shows a question mark, and slot 2 randomly alternates showing up as either S2 or not at all.

Anyone want to make any guesses as to what's up? CC protocol change? DSD+ bug? Operator error? I should point out that I can nearly see the tower this site is on. Signal strength is not an issue. I tried some attenuation and it made no difference. Another guess is that some timing/tuning might be off since it effects slot 2 on the CC too. Maybe the signal is skewed somehow due to multicoupler/transmit combiner tuning when they added an extra freq to the site. I am still working on the knowledge that would let me examine the waveform for these issues.

 

[EricCottrell]

Hello,

One feature of Con+ systems is over-the-air distribution of the network information file. It is a method of updating radios in the field by sending a data file to the radios.

You could make a raw audio file with DSD+ during the portion of the problem period and post it on a file-sharing site.

73 Eric

 

[RayAir]

Here is a screenshot of a MotoTRBO Connect Plus XRC 9000 Network System Manager.
Slot 1.2 shows an example of a File Transfer going on OTA.

I tried to get it more clear.

 

[BM82557]

Here is a screenshot of a MotoTRBO Connect Plus XRC 9000 Network System Manager.
Slot 1.2 shows an example of a File Transfer going on OTA.

I tried to get it more clear.

Could you upload the picture to somewhere like Zippyshare - Zippyshare.com - Free File Hosting then make a new post with the link to the uploaded file? Thanks.

 

[RayAir]

Could you upload the picture to somewhere like Zippyshare - Zippyshare.com - Free File Hosting then make a new post with the link to the uploaded file? Thanks.

https://www.dropbox.com/s/7n1f6ofwm4a9b8m/Con+ XRC 9000 System Manager.png?dl=0