[ale] Calculating bandwidth for serial terminals

[cfowler]

> 
> The problem -
> 
>  The serial terminals are running very slow. Much slower, in fact, than
> when they were on a multimux using a 56k leased line. According to the
> people who setup the network, the VPN has a bandwidth of "300k". I'm
> going on the assumption that he means 300Kbps. What I need to figure out
> is just how much of this "300k" is being used

.

#1 Standard speed wouuld be 9600 bits per second which equals 1200 bytes
per second.  That would be for each terminal.

#2 Serial printers should be for 2400bps.  It is possible that you can
have a serial perinter set up for 9600bps but most dot-matrix printheads
can only keep up with 2400.  Th other time is spent in flow-control.

#3 WCS you have 32 serial terminals.  Then you would expect to be using
up 37kbps if this was at full stream.  I doubt you are up to full
stream.  


> 
> 
> The questions -
> 
>  Is there a way to figure out just how much bandwidth is used by a
> serial terminal? Does the baud rate correspond, either directly or
> indirectly, with the amount of bandwidth used? Or, does the amount of
> usage have more to do with how much bandwidth is being used? I need to
> find out what is causing the slowdown, so I can find a way to fix it. If
> it's a bandwidth issue, I need to have figures in my hand to take to the
> client.

You know the above.  What you need to do is sniff the network and see
how much data is going between the 2 sites.  You see Mulit-Tech Mux is
much different than a Digi Terminal Server.  I would say that it is
possible to get much better speed over the Mux connection due to many
facters.  

#1 TCP/IP overhead:  Considering that each packet on a network has
multiple headers and ends up have one byte for data.  That is the key
pressed.  2 packets since that character is being echoed by the remote
system.  This is extreme overhead.

So the user enters the letter 'A' on the keyboard so one char goes back
to the remote site.  Nope wrong.

[Etherenet Header][IP Header][TCP Header]A

Notice all the crap before the A.  This is the overhead that you are
experiencing.  I alos assume that you are using Dig's "Real TTY' on the
SCO box to fake true serial ports.  That software in itself may hadd
more headers.  I'm not sure.  Oh yea if you are using ppp to do the VPN
you also have a PPP header.  

All I can say is as a result of this setup you've got much data going
between the 2 sites.  I could be wrong but this is my opinion and I
think others may have better ideas on how to fix.

> 
> 
> Pointers, places to RTFM, RFC's, websites and tutorials greatly
> appreciated.

The MUX truly is a fantastic piece of gear.  Sure it may be "old" and
not so sexy as technology is concerned but neither are Wyse 50's.



> 
> 
> Thanks,
> ...alan
> 
> -- 
> And on the seventh day, He exited from append mode
> (Linux fortune)
> 
> 
> _______________________________________________
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> Ale at ale.org
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