http://www.dslreports.com/forum/r20372212 en Tue, 02 Dec 2008 10:28:17 EDT Tue, 02 Dec 2008 10:28:17 EDT http://www.dslreports.com/forum/remark,20372212 Tursiops_G : Determining a "Proper" RWIN setting is dependent on Several Factors... (There Is NO "One-Size-Fits-All" Answer). ;)

This is just a "Rough Ballpark" method that I've found to be helpful... Experiment with it, and see if it helps...

Things you Need to Know:

Your Effective MTU (Maximum Transmission Unit) - Generally 1500 for Cable and for DSL using PPPoA, and 1492 for DSL using PPPoE (However, these values may vary with some ISPs)... Do a "Tweak test" from Here: »/tweaks ,or check with your ISP for the correct MTU setting for your particular Service.

Service Tier/Connection Speed (Max Download Speed).

Network Latency (Ping Time).

Network Packet loss (% of "Dropped" packets).

Next, Calculate your Base RWIN with this formula: MTU - 40 = MSS , MSS x 44 = RWIN.

Example: If Your MTU is 1492, then your MSS is 1452 (MTU - 40), and your Base RWIN is 63888 (MSS x 44).

Note that This is your *BASE* RWIN... This assumes that you have a Service speed of around 1.5Mb/s to 3Mb/s, with "Low" Latency, and Little to NO Packet loss issues.

Speed Adjustment:

If you have a Lower-speed Service (384Kb/s to 768Kb/s), then Divide the Base RWIN by 2 (ex: 31944).

If you have a Higher-speed Service (>3Mb/s to 10Mb/s), then Multiply the Base RWIN by 2 (ex: 127776).

If you have an Even Higher-speed Service (>10Mb/s to 15Mb/s), then Multiply the Base RWIN by 3 (ex: 191664).

If you have an EXTREME-speed Service (>15Mb/s to 30+Mb/s), then Multiply the Base RWIN by 4 (ex: 255552).

NOTE: You may find that your "Optimal" RWIN may fall somewhere BETWEEN these values... However, Note that the RWIN value Should ALWAYS be an EVEN MULTIPLE of the MSS.

Latency/Packet Loss Adjustment:

If you are experiencing "High" Latency (>150mS), then you may find that using a Higher scale value RWIN may work better.

If you are experiencing noticeable Packet Loss, then you will probably find that using a Lower scale value RWIN will work better.

Again, This is Just a Rough GUIDELINE that will (hopefully) help you to get your RWIN "Into the Ballpark"... As Always, YMMV. ;)

-Tursiops_G.
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If You're Unsure, "RTFM"... If You're SURE, "RTFM" Anyway. ;)]]> http://www.dslreports.com/forum/remark,20372212 Wed, 23 Apr 2008 00:47:46 EDT http://www.dslreports.com/forum/remark,20370948 Lanik : I didn't use any mathematical equation if that's what you're asking. I used my experience as what works for others with similar advertised speeds. You hang around here long enough you get used to what people recommend and you'll start getting the right idea. The formula was designed to be used with max latency and works quite well when you're on other side of the country not so well when you're almost sitting on top of DSLR. FWIW DSLR is in NJ somewhere.

Try this:
• Ping 134.79.252.133 its a router in Standford University.
• Now use the latency * 1.5 * 100 / 8 and you should get a pretty good RWIN in the range of sixty thousand or higher.

Makes sense or still clear as mud? :D
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"If it ain't broke don't fix it."]]> http://www.dslreports.com/forum/remark,20370948 Tue, 22 Apr 2008 20:38:42 EDT http://www.dslreports.com/forum/remark,20370907 ajm786 : Ok, can you please tell me how you arrived at that figure? That's what I want to find out. :-)]]> http://www.dslreports.com/forum/remark,20370907 Tue, 22 Apr 2008 20:30:02 EDT http://www.dslreports.com/forum/remark,20370690 Lanik : SpeedGuide/CableNut et all believe that higher RWIN value is better we don't. If a lower RWIN will get you your advertised speed then whats the point of using something insane like 513920? RWIN calculator is based off your latency, 43800 is a little on a low side but 128480 should be plenty.
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"If it ain't broke don't fix it."]]> http://www.dslreports.com/forum/remark,20370690 Tue, 22 Apr 2008 19:51:37 EDT http://www.dslreports.com/forum/remark,20367468 ajm786 : I am trying to tweak my RWIN values, and I'm lost. I don't know who to believe!

I have Comcast Business Cable DSL, and my speed is 8M/1M. Following the Tweak FAQ section on this site, I calculated my RWIN value to be 43800, but using the Speedguide TCP IP Optimizer, it calculates that my RWIN should be 513920!

Can anyone shed light on this and point me in the right direction?

Thanks!]]> http://www.dslreports.com/forum/remark,20367468 Tue, 22 Apr 2008 09:55:43 EDT