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Dial-up networking/ppp binary transmissions slowing down and freeze

Keywords: Dial-up networking/ppp transmissions slowing down and freeze
Summary: through my best ISP - PPP binary transmissions slowing down
Program: pppd 2.3.3 - dip 3.3.7o - kernel 2.0.35
Hardware: Intel Pentium 133  16 MB RAM  Rockwell K56Flex modem  2.1 GB EIDE HD
          UART 16550A
Description: I dial into my ISP successfully but binary transmissions slow down
like images , FTP , ETC

The problem is that after I connect to my ISP and I surf the
transmissions of binary data (pictures, compressed files, etc.) is
slower and slower and it goes with 242 bytes/sec - horrible at any site
at any time with any protocol.
But the ISP is working well under other OS-es and when I phoned them ,
they could only tell me that the modems are system
independently configured. (They run SunOs)
One of the other ISPs I tried runs perfectly, but the best is that I
want to fix.
The PPP debug from the working ISP file differs in only one thing from the
want I want to use is that the good one sets MTU to 576 no matter what
I use in ppp options file and the other one sets MTU 1500 automatically, which
can't be changed , too.
I use a Pentium-133 PC with a modem based on Rockwell  K56Flex Chipset.
I use 2.0.35 kernel with pppd 2.3 p3.
I use dip (since chat does not work correctly) to access my server, I
include the script at the end.
I've alredy tried:
-setting up the  ports correctly with setserial
- there's no shared IRQ, I use IRQtune to optimise the system
- setting pppd options (on and off) (like asyncmap 0 ,nobsdcomp+novj,-detach,
-Trying out different MTU-MRU, Window size values
- The phone line's quality is good. I always log in with >=28.8 as in
Windows.  The modem Init script is good.

Please e-mail me or post a message if you have any more suggestions.

  ViZo -

-----------------DIP Script -------------------
       port cua1
       speed 115200
       shell setserial /dev/cua1 uart 16550A spd_vhi port 0x2F8 irq 3
       shell /sbin/irqtune
       get $mtu 1500
       send AT&FE0V1&C1&D2S95=47S0=0\r
       # send AT&K3\r
       wait OK 5
         if $errlvl != 0 goto modem_trouble
         dial 1234567
        if $errlvl != 1 goto modem_trouble
         sleep 2
         print Waiting for login prompt...
 wait Username: 20
         send xyz\r
         wait assword: 20
         send xyz2\r
         send ppp\r
         wait is 20
         get $locip remote 20
         wait is 20
         if $errlvl != 0 goto ppp_error
         print IP $rmtip
         print CONNECTED $locip
         print MTU: $mtu
         mode ppp

         print The modem connection failed
         goto error

         print TIME-OUT waiting for PPPlogin to fire up...
         goto error

         print time-out waitin for ppp message
         goto error

         print CONNECT FAILED to $remote
         quit 1

Expected: Stable binary transmissions speeds.
1 Solution

If I understand all of the above correctly, you are having trouble with one ISP, and things work well with another ISP?

Slow down your serial port. Or upgrade your RAM. Or both!
Your machine is being flooded with information and your machine can't handle it.
Try some different,slower speeds and see what this does.

vizo2Author Commented:
I've already tried to slow down the serial ports and the connection, it doesn't use. And it doesn't explain why other ISP's do work perfectly. I'm not silly. I would change my ISP , but the one I use is free and good. Because my linux workstation
is configured now well and I want to use it for networking , too.
They use SunOs 5.6 but they can't explain the situation.
Thank you for your answer. And please help me.

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i got same problem on my a few linux(s). excetly the same. i also want to know the answer.


Try dialing one of the ISPs numbers long distance.  If it speeds up, then your telco has a bad switch.  What kind of equipment is the ISP using on their end?

Also you might want to check the manual and turn data compression off.

Always add the time tested AT&F1&C1&D2

Try adding +MS=11,0,9600,33600 and try setting that last value lower and lower (i.e. 28800, 26400, 14400, 9600, etc)

But in my opinion, it's either a set of equipment that doesn't like each other (like USR and Ascend), or a telco screw up.
vizo2Author Commented:
I use the same init string as in windows the perfect fo v.34 -mnp5,..
I also tried every combination and turning off compression methods.
The starnge thing that it's working well under other OSs and I use the perfect init code.
Other local-numbered ISPs work well.
And I don't know why the hell it is working under Windows perfectly and not under Linux.
But, anyway thanks for your answer but I tried to slow down the speed at 24000 , too, while others running at 26 <= are running cool.

Thank you,
vizo2Author Commented:
the ISP use Sun Solaris 2.56 based machines with 28.8 US Robotics modems.
I think it must be a bug between the two systems.
Change the PPP daemon with ppp-2.3.5. This PPP work great and I think I saw kinda problem with ppp-2.3.3 and linux kernel 2.0.3x.
vizo2Author Commented:
I've alredy tried it (as I've written down), and it is bad with linux 2.1.1, too. It doesn't work with other systems too, with only one it does but that's the worse service.

Alan Cox, who is responsible for most of the networking code
of linux, has reported a "slow network connection problem"
between linux and solaris:

He writes:
Slow FTP Linux<->Solaris 2.4 or 2.5
     Solaris has some very bad TCP problems over slow links. Sun have now released a patch set for Solaris 2.5
     103447-03 and 103169-06 ( )

also the same document mentions a problem due to MTU mismatch

Sessions work but the first large output hangs the link
     This is often seen over SLIP links when path MTU
     discovery is used. Previously you could normally get
     away with mismatched MTU's at each end of a slip link
     to Linux boxes. With Path MTU this is no longer true.
     Fix the MTU's. Also beware of some very old terminal
     servers that mishandle MTU discovery. If so turn
     MTU discovery off or use 1500 byte+ MTU's
     on the slip link.

The first one is related to your ISP (do they have the
patch installed?)

The second one is I think more likely in your case
you can try setting your MTU to be the same as used by
your ISP (576)

or try disabling MTU discovery
I am not sure how but
there may be a related setting in /proc
or you may have to recompile your kernel
(with relevant options)
try checking the kernel source/documentation

hope this helps...


you can fiddle with increasing your window and buffer sizes, but for it to really make a difference, you need to get your ISP to do it too..

check out url

for details..   it explains how you can performance tune almost any tcp implementation to achieve maximum throughput on slow networks..

good luck

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