PACKET RADIO: Quickfix for Many Problems
Steve Wolf, W8IZ@W8IZ
(This text from the W8IZ packet radio bulletin
board. It's formatted to fit a 80 character screen.)
From: Steve, W8IZ
To : ALL @ W8IZ
Date: 25 October 1990
Re : FRACK IT (and why you can not get throughput!)
Frack is a time delay. Let's say you send a packet out to a friend that
says, "hi there". After you transmit your packet, your station awaits for an
"OK-I got it!" from the other station. That is, it waits for an
acknowledgement packet or "ack". However, it will not wait forever.
Eventually, it will get tired of waiting and send your "hi there" again. The
time it will wait before sending information again is called the FRACK or
"frame acknowledge" time.
Typically, a TNC's frack is set to 3 seconds. That is, your TNC will
wait three seconds before resending the information if an ack is not received.
Most of you can check this by typing a control-C and then typing the word
FRACK. A three second frack is great for two users typing to each other.
A PBBS like MSYS is a different beast. MSYS is a MULTIUSER SYSTEM.
That is where the name of the program, MSYS, comes from. MSYS might not come
back and acknowledge your packets in three seconds. There may be other users
or MSYS might just be a snot. Yes, a snot. It is possible to configure your
TNC to be very, very aggressive. You could take over the channel and not let
anyone else use it. MSYS is protected against that. Every once in a while it
pauses a bit more than normal. MSYS might even adjust it's frack for poor
conditions. It might wait much longer in the hopes that a temporary anomaly
will go away.
IF FRACK IS TOO SHORT
If you have frack set too short, you might end up in the following
situation. This situation has been seen on about five stations on NO8M so
You send MSYS a packet of information. MSYS sets up the ack but does
not send it within the three seconds. You resend the information. MSYS
discards the ack and resets another ack and prepares it to be sent. You go
ahead and time-out again and send the information. You just keep sending
information and never wait to get an ack. Eventually, you retry out.
Now ... if you set DWAIT to 16 and TXDELAY for the absolute lowest
value you can manage, you will have your station set up to cooperate with
everyone else on frequency.
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