[drats_users] ERROR Correction in slow speed data

Fri Sep 20 18:11:11 PDT 2013

Thanks for the correction. Still learning...

Dan Metcalf -- KB3UUN
On Sep 20, 2013 8:46 PM, "John Davis" <jdavis at gtworks.com> wrote:

>  Daniel:****
>
> That is incorrect.  There is definitely FEC on the voice.  Check the JARL
> spec.  ****
>
> ** **
>
> R2D2 is normally happens in low signal conditions. In Icom’s
> implementation of the vocoder, once the signal gets so low that the AMBE
> chip cannot faithfully recreate the voice packets, Icom had the choice to
> either just mute the voice or allow a little of it through and hope you get
> some intelligibility before it gets too low. ****
>
> ** **
>
> Forward Error Correction adds extra bits in a complex algorithm when
> transmitted that can reconstruct a packet when a certain number of bits are
> missing on the receive end.  That allows a digital signal to still be
> reconstructed at a lower signal level than if there was no FEC.  FEC is
> kind of like parity bits on steroids!****
>
> ** **
>
> Some people using other digital modes criticize D-STAR for having the
> R2D2.  You will notice that when R2D2 is present, you can sometimes pick
> out another word or two that you would miss if they chose to mute it at
> loss of packets.****
>
> ** **
>
> John WB4QDX****
>
> ** **
>
> *From:* drats_users-bounces at intrepid.danplanet.com [mailto:
> drats_users-bounces at intrepid.danplanet.com] *On Behalf Of *Daniel Metcalf
> *Sent:* Friday, September 20, 2013 8:21 PM
> *To:* Discussion of D-RATS
> *Subject:* Re: [drats_users] ERROR Correction in slow speed data****
>
> ** **
>
> I don't think is does. That is why when you radio loses sync you get R2D2
> and others remain able to receive. If I read the protocol documents
> correctly it is all fire and forget much like the VOIP protocols mentioned
> before.****
>
> ** **
>
> On Fri, Sep 20, 2013 at 6:23 PM, Joel Black <w4jbb at charter.net> wrote:****
>
>  Okay, this goes against what little I have learned about VoIP traffic.
>
> I didn't think there was any FEC with voice.  That's why voice has
> priority on data networks that use VoIP.  Otherwise, if a data packet has
> priority, it would bump a voice packet.  When a voice packet is bumped, you
> lose bits of it resulting in choppy audio.
>
> I have experienced this when some of our first quasi VoIP locations came
> online.  Voice is live traffic.  Once it is said, it goes.  There's nothing
> to re-transmit.
>
> Without getting into the engineering (which will leave me drooling and
> nodding off to sleep), how does D-STAR use FEC on voice?
>
> 73,
> Joel - W4JBB****
>
> ** **
>
> On 9/20/13 3:57 PM, John Davis wrote:****
>
>  That is true. The FEC is on the voice with 2400 bits for voice and 1200
> for FEC.****
>
>  ****
>
> John WB4QDX****
>
>  ****
>
> *From:* drats_users-bounces at intrepid.danplanet.com [
> mailto:drats_users-bounces at intrepid.danplanet.com<drats_users-bounces at intrepid.danplanet.com>]
> *On Behalf Of *Daniel Metcalf
> *Sent:* Friday, September 20, 2013 4:55 PM
> *To:* Discussion of D-RATS
> *Subject:* Re: [drats_users] ERROR Correction in slow speed data****
>
>  ****
>
> Agreed. From what I have read d-star is a lot like the UDP network
> protocol where it is transmit and forget there is no handshaking / error
> correction built in. It is up to the application developer to handle error
> correction and the d-rats package does perform some level of error
> correction.****
>
> Dan Metcalf - KB3UUN.****
>
> On Sep 20, 2013 3:54 PM, "John Davis" <jdavis at gtworks.com> wrote:****
>
>  My understanding is that the low speed data channel does NOT have error
> correction, however, D-RATS offers Error correction in Message and File
> Transfer modes where it is most important.****
>
>  ****
>
> John WB4QDX****
>
>  ****
>
> *From:* drats_users-bounces at intrepid.danplanet.com [mailto:
> drats_users-bounces at intrepid.danplanet.com] *On Behalf Of *Dave Welker
> *Sent:* Friday, September 20, 2013 3:19 PM
> *To:* D-Rats Mailing List
> *Subject:* [drats_users] ERROR Correction in slow speed data****
>
>  ****
>
> Hello all,****
>
> Can anyone confirm if the D-RATS slow speed data has FEC (Forward Error
> Correction) built in now or not?****
>
> I understand that D-STAR voice does have error correction built in.  I've
> checked on the D-RATS home page/documentation****
>
> which is a August 2009 reference.****
>
>  ****
>
> This is what I found in this document Under users manual/files:  Is this
> still current information?****
>
>  ****
>
> *Unlike the D-STAR DV Voice Channel, which has error correction built
> into the protocol, the Data Sub-channel has no error correction. *****
>
>  ****
>
> *This makes the transfer of data across D-STAR a lot more dependant on a
> good radio path being established between the two locations wishing to ***
> **
>
>  ****
>
> *exchange data.  D-RATS includes the ability to test connectivity between
> two locations**.*****
>
>  ****
>
> Thanks in advance****
>
> regards****
>
> Dave****
>
> W2SRP****
>
>  ****
>
>  ****
>
> Goals are where we want to be;
> Objectives are the steps to get there.****
>
>  ****
>
> There are 2 rules to success in life:
> 1. Don't tell people everything you know.****
>
>
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>
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>
> -- ****
>
> Dan Metcalf -- KB3UUN****
>
> c. 301 769 1111****
>
> Amateur Radio has something for everyone. Even if it is just peace of mind
> that no matter what happens your message will get through.****
>
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