[aprssig] packet delays through internet

Stephen H. Smith wa8lmf2 at aol.com
Sun Mar 20 16:37:19 EDT 2011

On 3/20/2011 1:07 PM, Russ Chadwick wrote:
> Significant packet delays were noted through an I-gate that consisted of a 
> D710, UI-View and Comcast ISP.  We (Mark, KC0D; Nick, N0LP; and I) did tests 
> yesterday and found the problem to be that UI-View was using Xon/Xoff flow 
> control while the D710 was not using flow control.  Delays of a few minutes 
> to 90 minutes were noted with this set-up.
> After we changed UI-View to having no flow control, expected delays of just a 
> few seconds were noted almost all of the time.  In addition to the delays 
> becoming normal, the problem with bad characters in the I-gated packets also 
> went away.
> At 2000 on March 19 we started a test where a timestamped packet on 144.340 
> MHz was sent to the I-gate every minute.  This test continued overnight to 
> 1800 on March 20.  The results for each packet can be viewed here,
> http://www.findu.com/cgi-bin/raw.cgi?call=KB0TVJ-4&time=1
> Russ  KB0TVJ

Arrrgh!!!     Xon/Xoff is asking for trouble, especially on radio data links,  
since any value from Hex 00 to Hex FF is possible in an incoming byte, 
especially if it is corrupted in any way.    Xon/Xoff flow control consists of 
binary characters transmitted over the same TXD/RXD conductors as the incoming 
and outgoing data.

o     X-Off is actually the same character as "Ctrl-S" a.k.a. "DC3"   (Hex 13)

o     X-On is identical to "Ctrl-Q"  a.k.a.  "DC1"  (Hex 17)

Did you try hardware handshaking (CTS/RTS conductors) on both ends?   This 
would appear to be the most positive flow control, assuming the cable between 
the two devices has the conductors required.

By the way, did you ever determine where the numerous corrupted versions of the 
two balloons' callsigns that appear on my maps came from?   It would appear 
that somewhere, someone was running an igate or digipeater in PASSALL  a.k.a. 
"junkque" mode.

It could have easily been these corrupted packets retransmitted to your igate 
that choked it with bogus X-on/X-off characters.....



Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      WA8LMF  or 14400    [Think bottom of the 2M band]
Skype:        WA8LMF
Home Page:          http://wa8lmf.net

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