Tursiops_G
Technoid
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join:2002-02-06
Norwalk, CT
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| reply to ajm786
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. |
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