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From: Rick H Kennerly (no email)
Date: Sat Nov 02 2002 - 18:57:24 EST
It's not so much a throughput question but rather a connection question and
quality of connection question.
While Susan reports good luck with Sailmail, she's also sitting--in a radio
sense--right in the backyard of the antenna. But these systems are not "on
demand, multiple connect or token ring passing kinds of systems distributed
server systems. Instead, these radio e-mail systems these are one to one
transactions.
Down here in the Carib radio e-mail connections are pretty good for Sailmail
and Airmail (ham) all summer long, but wait until the cruisers return for
the winter season. In the radio e-mail business it's a one to one network
kind of distribution. That means that the radio service can only serve one
cruiser radio at a time and each connected cruiser can have ~20 minutes
connect time per day (depending on the service rules). And there is no
orderly queue, take-a-number-and-wait, or sign-up sheet to be served next by
the radio server.
Instead the radio e-mail systems are like a teacher and a class of unruly
kids. The teacher asks the question, "who has something he or she wants to
say?" and at each desk hands go up and the students all scream, "me, me. me,
me, me." And from that confused mess the teacher selects a student who then
gets to occupy the teacher's undivided attention until that student's time
runs out or the student has nothing more to say. Of course, this teacher
isn't so bright, so he selects the loudest signals first (mostly because he
can't hear the weaker, more distant signals through the clutter). You can
see where I'm going with this...
The farther from the main antenna you are (leaving atmospherics out of this
for the time being) or the weaker your signal is and the more competition
there is for the server radio's undivided attention, the longer you'll have
to wait. During the winter down here, I've spent 12-hours or more flipping
around from "server" to "server" trying to be heard and get a connect.
Not only that, but when you do get a connect, not everyone in the class is
waiting for the teacher to finish with you but is busy screaming, "me, me,
me, me" all the time you're trying to talk, seriously degrading your
throughput because of all the "repeat" packets being sent. Then there are
commercial radio operators on big ships running enormous linear amplifiers
that put out 5 times the power of any Ham or Marine SSB unit.
All in all, for cruiser to cruiser contact, voice SSB or cruising HAM nets
deliver much more information much more efficiently.
Rick Kennerly, NH2F
Rick the Mouseherder
Xapic, Westsail 32
Cabo San Juan, Puerto Rico
www.mouseherder.com/xapic
www.westsail.org
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