PACKET RADIO: DON'T BEACON (PLEASE!)
(This text from the W8IZ packet radio bulletin
board. It's formatted to fit a 80 character screen.)
Imagine yourself during the evening drive-time talking
to a friend on a popular two meter repeater. Every time
you or your friend drops the mike, everyone listening
announces they are there and says, "Beacon!". That would
be enough to drive you to simplex.
That is essentially what a beacon does, it robs time
from other users of the channel. Like a two meter repeater
a packet channel is not multi-tasking. Never has been
and never will be! Two stations, one of which is
transmitting, are using the frequency at any one time.
A beacon can do nothing but hold up that flow of
information.
A good example of a beacon's result can be seen on
145.01 or 223.7, the two forwarding frequencies used in
our area. Listen on a Friday evening, during the summer,
when the band is wide open.
ALOHA
Aloha! Neat word but death to packet radio. Aloha
happens when there is too much activity on a channel and
nothing can get through. A TNC waits until the frequency
is clear to transmit its information. However, it can
not wait forever. When the timers time-out, it goes
ahead and send its information on top of whatever is on
the band. The channel can only support so much activity.
With a couple of nodes forwarding traffic, a person
or two using a PBBS and two or three LANs hearing each
other, the frequency will be constantly buzzing with
packets. Add a beacon and pow, a TNC times out and
transmits over another packet. The frequency is still
active. The two TNCs that had collided now time out over
another TNC or two. Timers again time out and this time
the frequency goes quiet. All have collided and Aloha
exists. All you hear are beacons.
WHAT CAN YOU HEAR?
Can you hear REP, the Republic, Ohio, node. How
about AKR? And MTG? Probably not. You can hear CLE
though, can't you? Well, CLE hears REP, MTG, AKR and
a ton of other nodes. CLE hears you. When it is time
for your beacon to be sent, you will patiently await a
clear frequency and then send. You will send right over
REP talking to CLE. CLE looses the packet, ignores
REP and REP must wait for a timeout to resend the packet.
Aloha begins.
WHAT DO PBBSs HEAR?
Much of the same on the channel you are listening on.
However, there are five other ports that may also be
listening. It is not at all unusual on the NCARC PBBS
to have two users on 145.09 while the board is forwarding
mail on 223.7. Maybe someone is using the K Node, too.
Every incoming packet must be decoded and attended
to. A beacon must be received, decoded and discarded.
Even for a very fast machine, a busy channel will slow
it down noticeably. Even on a non-busy frequency, the
PBBS might be working its little processor off on other
ports.
HOW CAN THE NETWORK KNOW I'M ON?
Take out an ad in QST. Ask a newsletter editor to
publish you information. Put a message on a PBBS. Tell
your friends on VHF.
WHY DO PBBSs BEACON
Why they beacon every ten minutes, I don't know.
The NCARC PBBS beacons at intervals of a little over 24
hours. Software exists that can be set up to monitor
PBBS beacons. With PBBS beacons, there is a mail call.
This software looks at the mail call and if it recognizes
the call of the owner, it will call the board and retrieve
the mail.
If the software were designed to call the board
and retrieve the mail, it would eliminate beaconing
all together.
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