[Xastir] Smart RELAY digipeating

[BDonnell at ar-northwest.com]

> -----Original Message-----
> From: Wes Johnston [mailto:wes at kd4rdb.com]
> Sent: Wednesday, January 05, 2005 4:30 AM
> To: Bob Donnell
> Cc: archer at eskimo.com; oh2kku at iki.fi; xastir at xastir.org
> Subject: RE: [Xastir] Smart RELAY digipeating
> 
> 
> Ummm.... I've been watching this thread and think the idea is 
> to not digipeat
> RELAY by a home station if you have already heard the same 
> packet digipeated by
> the local WIDE.  That's a great idea.  So your station sits 
> on the packet for 3
> to 5 seconds before digipeating.
> 
> In the past few days is where I've gotten confused.  There 
> seems to be talk
> about KISS tncs delaying the delivery of a packet to the 
> network.  If what I've
> seen is correct, it is being said that the kiss tnc can cause 
> the delay.  Yes,
> it can, but if the packet is heard digipeated from the WIDE, 
> that KISS mode tnc
> isn't going to care... it's got "data" in queue and is just 
> waiting for access
> to the channel.
> 
> The trick to make this work _correctly_ is to use 6-pack 
> TNCs.  They communicate
> the busy/clear status back to the host computer.  Unlike KISS 
> tncs, you can't
> queue a packet in the tnc for minutes at a time... the host 
> must watch for the
> channel to be free, and as soon as it is, the host must start 
> sending data
> forcing the TNC on air.  This of course moves the host 
> computer one step closer
> to the radio and allows us to abort digipeating a relay packet.
> 
> Sure is a shame that KISS tnc's don't communicate the CD led 
> status via one of
> the rs232 handshake lines.

I think SOME TNC's can be configured to communicate the status of the CD line.  However you still have the delays imposed by transferring the entire packet to the computer (and that has to be allowed for) and transferring the entire packet from the computer back to the TNC.  If the RS-232 data rate is fast, say 19200 baud or faster, the delay is pretty small, but still present.  

If the duplex state of the TNC isn't modified, or alternatively, the p-persistence, to make the TNC very aggressive, then the TNC can still add in significant delay.

Curt and I had an off-list discussion some time ago (a year?) about adding 6-pack into xastir, for this very reason. 

Bob, KD7NM


> 
> Wes
> --
> 
> 
> 
> Quoting BDonnell at ar-northwest.com:
> 
> > > -----Original Message-----
> > > From: Curt, WE7U [mailto:archer at eskimo.com]
> > > Sent: Tuesday, January 04, 2005 9:00 AM
> > > To: Tapio Sokura
> > > Cc: xastir at xastir.org
> > > Subject: Re: [Xastir] Smart RELAY digipeating
> > >
> > >
> > > On Tue, 4 Jan 2005, Tapio Sokura wrote:
> > >
> > > > Still I'm a bit sceptical about this
> > > everyone-transmits-at-the-same-time
> > > > approach when there are stations involved that don't use
> > > the digipeating
> > > > functions of a conventional TNC. I have mine in KISS mode
> > > so some delay
> > > > is added from the serial communications (both ways) and from the
> > > > processing occurring on the computer. When the packet gets
> > > back to the
> > > > TNC from the computer to be digipeated, the channel is
> > > probably already
> > > > occupied from the digipeats by other stations. But I'm 
> not saying it
> > > > can't work..
> > >
> > > Understand.  You'd have to tweak your KISS settings so 
> that station
> > > was much more agressive on channel.  That'd be fine for 
> igating but
> > > not for normal operation.
> >
> > When using serial KISS mode, Xastir could make those TNC 
> settings changes
> > interactively.  Perhaps the easiest would be to set the TNC 
> to full-duplex
> > mode - that should assure a collision-rich environment...
> >
> > 73, Bob, KD7NM
> >
> > >
> > > --
> > > Curt, WE7U.   APRS Client Comparisons: 
> http://www.eskimo.com/~archer
> > > "Lotto:    A tax on people who are bad at math." -- unknown
> > > "Windows:  Microsoft's tax on computer illiterates." -- WE7U
> > > "The world DOES revolve around me:  I picked the 
> coordinate system!"
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