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PA2AGA > HDDIG 01.03.00 06:14l 151 Lines 5551 Bytes #-9562 (0) @ EU
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From: pa2aga
To: hd_broadcast@pa2aga
Subject: HamDigitalDigest 2000/60C
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>and possibly full duplex last mile because half duplex just doesn't
>work beyond one or two hops and we need to span 30 or 40 hops.
Yes. We can support full duplex, and our sites generally use RF modems
on different bands for alternating backbone hops. That way they don't
interfere with each other, and the switch site can stream in both directions
along the backbone at the same time. Most of the users are still running
half duplex, but we have made provision for them to operate crossband
duplex. This eliminates the need for an expensive repeater grade in band
duplexer at each user's site. We don't have many users taking advantage
of that though. It does require a receive converter in addition to the normal
transverter, and a pair of antennas. That's still cheaper than a duplexer,
but most users don't perceive enough benefit to do it.
Gary
Gary Coffman KE4ZV | You make it |mail to ke4zv@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
>.
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Date: Mon, 28 Feb 2000 23:31:32 GMT
From: nomail@rob.knoware.nl (Rob Janssen)
Subject: Internet over packet?
Gary Coffman <ke4zv@bellsouth.net> wrote:
>>while we are at it, we should also be developing full duplex backbone links
>>and possibly full duplex last mile because half duplex just doesn't
>>work beyond one or two hops and we need to span 30 or 40 hops.
>Yes. We can support full duplex, and our sites generally use RF modems
>on different bands for alternating backbone hops. That way they don't
>interfere with each other, and the switch site can stream in both directions
>along the backbone at the same time. Most of the users are still running
>half duplex, but we have made provision for them to operate crossband
>duplex. This eliminates the need for an expensive repeater grade in band
>duplexer at each user's site.
I should say that I completely miss the basis for the claim of needing full
duplex because of a certain number of hops, and the need for 30-40 hops,
but aside of that: in Europe we usually use in-band fullduplex for links,
and DF9IC has designed a couple of easy-to-reproduce duplexfilters for that
purpose. They are available ready-made from some amateur and commercial
sources as well, usually at affordable prices.
Full-duplex to the user is normally not feasible (a separate transceiver at
the node side for each user!?), but some nodes use a hybrid system:
full duplex system including duplexfilter at the node, halfduplex-split
system at the user side. node can transmit data all the time, users
transmit one by one.
Channel access can be controlled by bit-repeating the uplink to the
downlink at the node, which has the advantage of allowing user-user
connects, or by using DAMA or OPTIMA, which allows for better throughput
but needs fast user transceivers.
Rob
--
+----------------------------------+--------------------------------------+
| Rob Janssen pe1chl@amsat.org | WWW: http://www.knoware.nl/users/rob |
| AMPRnet: rob@pe1chl.ampr.org | AX.25 BBS: PE1CHL@PI8WNO.#UTR.NLD.EU |
+----------------------------------+--------------------------------------+
>.
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Date: Tue, 29 Feb 2000 08:51:09 +0200
From: Paul Keinanen <keinanen@sci.fi>
Subject: Internet over packet?
On Mon, 28 Feb 2000 23:31:32 GMT, nomail@rob.knoware.nl (Rob Janssen)
wrote:
>I should say that I completely miss the basis for the claim of needing full
>duplex because of a certain number of hops, and the need for 30-40 hops,
If the technical quality of each link is so good that you only get
only a few single bit errors each hour, you can use simple bit
regeneration at each hop, then there is no need for individual
acknowledgement at each hop. The high reliability of each hop is the
case with Frame Relay, in which case you only have end to end
acknowledge is required, possibly with a very large window size.
You can of course improve the quality of each hop by using strong FEC,
thus reducing the number of retransmissions required, but this also
increases the propagation delay, since a whole frame must be received,
the ECC applied to the data and a new frame must be generated from the
_corrected_ data, thus much more time is required than in simple bit
regeneration.
With 30 - 40 hops, you can reach about 1000 km assuming 30 km hops,
which is about the practical maximum for high speed communication in
all weather conditions.
Paul OH3LWR
>.
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Date: Mon, 28 Feb 2000 12:12:16 GMT
From: n1naf@mint.net.net (Michael Francoeur)
Subject: Kantronics KTU weather station on APRS
Has anyone put a Kantronics KTU weather station on APRS. If so, how
did you do it?
Please send responses to my callsign @ mint.net.
- Mike (N1NAF)
>.
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Date: Sun, 27 Feb 2000 09:01:30 +0300
From: A <sn_tst@gmx.de>
Subject: ml
--
Привет!
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