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Optimizing ADSL connections
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Fresh-Faced Recruit
Join Date: May 2003
Status:
Offline
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Hey,
With an asynchronous connection, download speeds can be affected by heavy upstream activity. This occurs because after you recieve a TCP packet, you are supposed to send an ACK back to verify that you have recieved it. If your upstream is saturated, the ACK gets queued and if it taked to long to get it out, it screws up the download.
The document: http://www.benzedrine.cx/ackpri.html describes a method for fixing this problem in OpenBSD. Basically, he sets the computer to prioritixe the ACK instructions in the TCP queue. My question is, is this possible in OS X? How?
Thanks!
PS: I cross-posted this is OS X, Unix, and Networking. Feel free to lock/delete if this is a breach of etiquette.
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Grizzled Veteran
Join Date: Sep 2002
Location: Silicon Valley, CA
Status:
Offline
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Originally posted by theseum:
Hey,
With an asynchronous connection, download speeds can be affected by heavy upstream activity. This occurs because after you recieve a TCP packet, you are supposed to send an ACK back to verify that you have recieved it. If your upstream is saturated, the ACK gets queued and if it taked to long to get it out, it screws up the download.
The document: http://www.benzedrine.cx/ackpri.html describes a method for fixing this problem in OpenBSD. Basically, he sets the computer to prioritixe the ACK instructions in the TCP queue. My question is, is this possible in OS X? How?
Thanks!
PS: I cross-posted this is OS X, Unix, and Networking. Feel free to lock/delete if this is a breach of etiquette.
look for something called BroadbandOptimizer
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MacBook Pro 15" Unibody | iPhone 16GB 3G
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Administrator  Join Date: Apr 2001
Location: San Antonio TX USA
Status:
Online
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theseum,
You describe the situation very well, and in nicely understandable terms. One thing to note about this problem is that it takes a LOT of upstream traffic to slow your downloads if your connection, modem, router, etc. are properly configured. Of course if your ISP doesn't ensure that THEIR part of the connection is optimized, you can do anything you want to YOUR part and still not see any improvement.
Another issue is the difference between your upstream and downstream speeds. My ADSL connection gives me up to 1.5Mbps down with up to 125kbps up. This is fine for surfing, streaming files, etc., and usually isn't a problem with a single user playing online games. If I was serving files through this connection, I'd have serious problems with downloads while files were going out. Moral: if you plan to serve, buy a big enough connection.
A few tweaks I can suggest include optimizing the connection between your modem and router (ensure you have really high quality ethernet cable between them, and keep it short-a 1meter Cat5E cable is worth the price here), and making sure your router's MTU setting is appropriate; with most DSL connections it should be set for 1492, though WAN conditions and ISP settings may call for lower settings. Your best bet for objective measurements of your connection and great hints for optimizing what you can is to go to Broadband Reports' Tools page. Use the tools to measure your speed, and the tweaks forum to find ways to go faster.
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Glenn -----
OTR/L, MOT, Tx
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Dedicated MacNNer
Join Date: Jul 2002
Location: Boston, MA
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