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[aprssig] Re: More thoughts on Connected Packet - telpac_node

Spider spider at rivcom.net
Thu Dec 30 03:58:06 UTC 2004


----- Original Message ----- 
From: "Ray McKnight" <shortsheep at worldnet.att.net>
To: "'TAPR APRS Mailing List'" <aprssig at lists.tapr.org>
Sent: Wednesday, December 29, 2004 5:30 PM
Subject: RE: [aprssig] Re: More thoughts on Connected Packet - telpac_node




Most stations connect to Winlink via HF over PACTOR-III.
It is possible to achieve a 3.6kb data rate via this method.
Yes, over HF, it can be THREE TIMES faster than 1200 baud
Packet!  This is due to the advanced compression and signal
Processing built in to the PTC modems.


The compression that is in Airmail compresses typical text messages up to 
40% by what I've seen in my messages.  This greatly help the total 
throughput on any system.  Typically I see ~20% compression.  In any case, 
dozens of messages
can be sent in less than a few minutes....nominally making it "fast enough". 
You have to keep in mind it is not there to replace with the agencies we 
serve already have, it's a last ditch effort at getting the mail through. 
That is what we are there for as hams.


I believe the intent on adding Telpac was mainly for Hams who don't have a 
license to operate on HF.  Telpac gives
Them the ability to get into the system using existing, inexpensive 2 meter 
packet gear.


I don't know I was not there.  However, I think they soon realized that it 
was a great addition to the WL2K network as a whole.




 This method also opens the door for other innovative things like WiFi and 
other wireless implementations
at the LOCAL LEVEL, or "last mile" as they refer to it.

Well, I do not see why it would not work although I read where it was not 
the intent to make things like that work.
Shoot, all it is, is a TelNet connection.  How hard could that be for the 
programmers to make work?

>  But
>we shouldn't overlook the fact that Telpac will be very slow
>delivering that "last mile" when the data has to pass through
>the 1200 baud packet pipe to the end user.

I disagree.  Let me tell you why.  I was in a Remote Comm Unit (RCU)in La 
Paz County during the State Disaster Exercise.
I had a County Comm Unit parked next to me with no Email Capability and I 
had a State Comm Unit (TOAD1) parked on the other side of me.  (I might 
add...okay I am bragging...my 30kw Onan portible Gen, Burtha, powered all 
three units and did not sweat!!!) One of the goals was to give Winlink a 
good test....I was not sold on it until that day.
I set up a Telpac node...took about 20 minutes earlier in the week...I had 
an Elmer point me in the right direction with some questions I had.  I then 
had the EOC, Tod, K6SUD set up with Airmail....I had two very capable 
operators I let handle the EOC in Parker.  They had never used Airmail up 
till a few days before the event.
Except for some quick voice communications, the EOC and the RCU used 
Winlink.  Mail flowed freely and the slight delay was really not measured 
any different than a normal email run.  Most messages were under 2k and 
compressed to practically nothing.  Now, during this time, the State unit 
was having Sat problems at first and I really do not know if they ever got 
it going to use it for the event.  At the same time messages were going to 
and from the RCU and the EOC,
messages were being sent to and from the State EOC and three other western 
counties in AZ... Yuma, Yavapai and Mohave.  In the middle of all that I 
included emails to our County EM and a few others.  It actually worked 
without a flaw.  I ended up with three CRIT dispatchers in my unit sharing 
radios all wishing they had what I had at the time.
I might add that the Comm Inspector was also very impressed with the email 
use.....and I might also add one of the main National Guard Comm Units mucky 
mucks finally convinced me to give it a try....although they run HF Pactor.

You can argue all day long about it not working good enough and those that 
are using it will continue to get the comm job done.  All I can say is that 
it is in a growth stage and a development stage and it is doing good.  I 
personally enjoy the automation in sending and receiving Airmail provides 
and I enjoy a slight increase in security....you just cant pop up with a tnc 
and "read the mail" like normal packet.

> Because they are
>using only TNC's there is no benefit from the advanced compression,
>at least that's what I see here.

There is a 10 to 40% benefit in total throughput.


 But if a WiFi link can be
established directly to a Telpac node, then you have something
to brag about, and it should be very fast!


I am sure it can be done...I do not know why not.  I am sure if that is a 
popular suggestion to the authors, in time I think it would likely happen. 
I know D-Star is being talked about and the ethernet connect should not be 
that hard to do.



There is also a trade-off by the use of Airmail as the mail
Client (or ANY client for that matter other than ASCII), as
They all add some overhead for processing.  This increases the
Amount of data needed to send and receive messages, but probably
The convenience of a nice user interface outweighs that downside.

The handshake and message counting at the beginning of a connect is where 
the time comes in.

>Of course, the biggest drawback of Telpac is that it's
>Basically all done line-of-sight, local to the node, and
>Thus offers no benefit outside the local area.

Uh.... That is an advantage, not a disadvantage.




 Having
>Only 479 nodes worldwide, being that modes nodes are located
>Near metropolitan areas, there's a good chance many won't be
>Of benefit during a disaster.


That's because you have not got your's up and running yet....quit talking 
yourself out of it and just do it!  We'd then have 480 nodes and you would 
serve your local area well!

You know, everyone has talked about "Networks" since the day packet began. 
I admit most of my network  was toward So Cal and between KB6CRE and myself, 
we had radios on darn near every major mountain there was in So Cal, Western 
AZ and Nevada.  I had 9600 baud Links, I had 220 Mhz 2400 baud links into 
Arizona, I had 6 meter 4800 baud links and Nodes just all over the place and 
you know what...it really sucked.  It ended up having so much ham crap on 
it, it was near impossible to ever use it for anything useful!  So all this 
Network talk I hear is going in one ear and out the other....I hear nothing 
new and that we already knew 20 years ago.

73

Jim, WA6OFT









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