Need help with dialup connection (and syn packets)

Need help with dialup connection (and syn packets)

[Ed W]

Hi, I have a dialup connection (yes they still exist) and PPP with 
demand dial.  I have a problem with the exponential backoff sending new 
SYN packets when creating a new tcp connection. The problem is that the 
dialup connection takes around 23 seconds to complete (and then hangs up 
10 seconds later due to inactivitity), but by then the gaps between SYN 
packets is very long...

Unfortunately most operating systems send an initial SYN, then 
exponentially backoff with intermittent resends, say after 1 sec, 2 
secs, 4 secs, 8 secs, 16 secs, etc.  So what we observe is that because 
the dialup connection takes so long to complete, by then the tcp 
connection is only trying quite intermittently to connect, eg you might 
well wait another 8+ seconds before the next syn is resent, quite easily 
my demand dial connection will hangup before the retransmit is even fired...

Does anyone have any suggestions on how I might fake this a little? I 
effectively desire to simulate buffering syn packets before the PPP 
connection comes up?

Thanks for any off the wall thoughts...

Ed W

Re: Need help with dialup connection (and syn packets)

[John Lauro]

Sounds like the main problem is your aggressive hangup due to
inactivity.  It should be at least 4 times as the connect time, not
under half!.  I suggest 6 minutes, but at least 2 minutes.

If you can't adjust that, probably the next best alternative is a
pre-emptive ping or something to wake up the modem about 25 seconds
before you want to connect, or just ping every 5 seconds until you get
a successful response

On Sat, Mar 23, 2013 at 12:33 PM, Ed W <lists@wildgooses.com> wrote:
> Hi, I have a dialup connection (yes they still exist) and PPP with demand
> dial.  I have a problem with the exponential backoff sending new SYN packets
> when creating a new tcp connection. The problem is that the dialup
> connection takes around 23 seconds to complete (and then hangs up 10 seconds
> later due to inactivitity), but by then the gaps between SYN packets is very
> long...
>
> Unfortunately most operating systems send an initial SYN, then exponentially
> backoff with intermittent resends, say after 1 sec, 2 secs, 4 secs, 8 secs,
> 16 secs, etc.  So what we observe is that because the dialup connection
> takes so long to complete, by then the tcp connection is only trying quite
> intermittently to connect, eg you might well wait another 8+ seconds before
> the next syn is resent, quite easily my demand dial connection will hangup
> before the retransmit is even fired...
>
> Does anyone have any suggestions on how I might fake this a little? I
> effectively desire to simulate buffering syn packets before the PPP
> connection comes up?
>
> Thanks for any off the wall thoughts...
>
> Ed W
> --
> To unsubscribe from this list: send the line "unsubscribe netfilter" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Need help with dialup connection (and syn packets)

[Ed W]

Connectivity costs $1.50/minute.  You pay for 20 second increments. 
Speed is 2.4kbits (20KB/min)

It's a dial on demand router for a satellite based system

Any other thoughts?  I'm obviously going to look at application specific 
proxies, but I guess I'm hoping that someone might put me on to some 
clever ideas to buffer packets or duplicate them with delay...

Thanks

Ed W


On 23/03/2013 21:11, John Lauro wrote:
> Sounds like the main problem is your aggressive hangup due to
> inactivity.  It should be at least 4 times as the connect time, not
> under half!.  I suggest 6 minutes, but at least 2 minutes.
>
> If you can't adjust that, probably the next best alternative is a
> pre-emptive ping or something to wake up the modem about 25 seconds
> before you want to connect, or just ping every 5 seconds until you get
> a successful response
>
> On Sat, Mar 23, 2013 at 12:33 PM, Ed W <lists@wildgooses.com> wrote:
>> Hi, I have a dialup connection (yes they still exist) and PPP with demand
>> dial.  I have a problem with the exponential backoff sending new SYN packets
>> when creating a new tcp connection. The problem is that the dialup
>> connection takes around 23 seconds to complete (and then hangs up 10 seconds
>> later due to inactivitity), but by then the gaps between SYN packets is very
>> long...
>>
>> Unfortunately most operating systems send an initial SYN, then exponentially
>> backoff with intermittent resends, say after 1 sec, 2 secs, 4 secs, 8 secs,
>> 16 secs, etc.  So what we observe is that because the dialup connection
>> takes so long to complete, by then the tcp connection is only trying quite
>> intermittently to connect, eg you might well wait another 8+ seconds before
>> the next syn is resent, quite easily my demand dial connection will hangup
>> before the retransmit is even fired...
>>
>> Does anyone have any suggestions on how I might fake this a little? I
>> effectively desire to simulate buffering syn packets before the PPP
>> connection comes up?
>>
>> Thanks for any off the wall thoughts...
>>
>> Ed W
>> --
>> To unsubscribe from this list: send the line "unsubscribe netfilter" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html