At 10:32 PM 4/27/99 +0200, Dennis Dibbets wrote:
>Hi Guy's,
>
>I've got a problem. I'm using the ax25-protocol with a Baycom modem. I use
>ftp a lot to upload data to other hosts. But when i do this, my computer
>transmits too much at a time. This causes that the whole channel fills up,
>so that no other station in the area can work on the channel. I've set my
>mtu to 256.
>
>I've been told that the problem is the MRU-Setting. If it is the MRU, how
>can i configure this. In the manual of ifconfig is nothing to find about
>the MRU.
>
>If it ain't the MRU, what other thing can caus this?? I'm not so familiar
>with Linux, but i managed to get AX25 working under Linux..., that wasn't
>easy...
Hi Dennis,
Another approach is to make your system more "polite" at the AX.25 layer.
This is normally done by adjusting a parameter known as P-Persistance. It
is usually set to be (1 / number of channel users), assuming that the
number can be varied between zero and one.
Most TNC implementations offer a numeric range between zero and 255. So
the formula for computing the P-Persistance becomes (256 / number of
channel users). The theory here is that when your system has data to
transmit, it generates a random number from zero to 255. It checks to see
if the channel is already busy, and if not, then it compares the random
number with the P-Persistance number you calculated. If the random number
is less than the P-Persistance number you have configured, then the
transmitter will be keyed, and the packet will be transmitted. If the
random number is higher than the configured P-Persistance number, the
transmission is not made.
At this point another parameter, refered to as Slot Time come in to play.
It determines how long to wait before trying to generate a new random
number and repeating the process above.
The theory behind setting slot time is that it should be equal to the
amount of time it takes your station to determine that the channel is busy,
once another station has started a transmission. Normally for 1200 bps
packet, this is set for 100 milliseconds, and is normally a good choice,
considering the radio/TNC combination at most stations.
If you set the Slot Time to a larger value, or the P-Persistance to a
smaller value, you become a more polite neighbor on the channel. You may
still occupy a large percentage of the channel's capacity, however you will
wait longer (giving others more of a chance to get their data through)
before each transmission you make. If no one else keyed up, then the fact
that you occupied the channel just means that at least someone is making
use of the available bandwidth, rather than it going to waste.
I've not looked for the window size setting for a TCP connection in the
linux setup for a long time, but I think that's really the value you will
need to reduce if the concern is how long your longest transmissions
become. The window size governs how much data the connection will commit
to having in transit (not acknowledged) before it allows more data to be
queued for transmission.
Hope that one of these options helps you out!
73, Bob KD7NM
-----------------------------------------------------------------------
Bob Donnell, KD7NM [EMAIL PROTECTED] [EMAIL PROTECTED]
Western Washington Amateur IP Address Coordinator (425) 775-3651
--------------------- http://wetnet.wa.com/~kd7nm ---------------------
