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[aprssig] Delayed Packets

Stan Coleman N0YXV n0yxv at gihams.org
Mon Oct 24 03:29:50 UTC 2005


We have what I think is a unique thing happening in our town. On several
occasions now we've had packets show up minutes if not hours later after
they were transmitted. On Saturday we had a mobile that would show up on one
side of town then back at his home. I guess (from what I was told) that it
ping ponged across town several times. I did look up my RF log from Saturday
morning and didn't find ANY duplicates. I didn't see this event but I did
experience the event in the next paragraph.

I had an occasion where I went to work and well over an hour after I got to
work I saw a packet coming in from my car. This was a little bit worrisome
but it was showing still in the packing lot. After the third packet from the
parking lot I got up and went out to check my car. Nobody had been in my car
and it wasn't on. Those packets turned out to be repeats that had occurred
well over an hour before.

In town we only have one Digi (that I know of) and that is WY0F. We do
however have three full time IGates and 2 others that can be IGates at any
one time. If you pull up our town that's a huge number of IGates in a very
small area. Now here is my question, "Is it possible for all of these IGates
to be transmitting packets to that APRS network (Internet) at slightly
different times?" (See my guess below for a better explanation.)

Let me know if I'm really off base but here is my guess as to what happens.
Packet A gets IGated at two or more locations. Location one is using a Tier
2 server and location one is using a Tier 1 server (different servers in any
case). If the packets taking the longest path gets buffered anywhere along
the path that might be enough delay to cause the repeats. The packet going
through Tier 2 gets delayed enough to look enough different than the packet
going through Tier one that the system thinks they are two different packets
and puts both into the system. Thus making the vehicle appear to bounce
between two locations. Since we basically are using what amounts to telnet
packets and not a streaming system some routers put telnet packets at the
lowest end of their queue systems.

Almost everyone in town is IGating using UI-View and I'm (N0YXV-1) IGating
with Javaprssrvr. IGates are WY0F, KC0MWM, N0YXV-1, Digi is WY0F. The whole
system is WIDEn-N compatible.

If my theory is true I think the only fix would be to make sure that all
IGates in a local LAN area use the same internet server.




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