Need help with dialup connection (and syn packets)
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
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
Quoted 26 lines · 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
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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
Quoted 36 lines · 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
Quoted 26 lines · 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
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