# Thread: How to calculate rwin

1. Member
Join Date
Jun 2009
Posts
21

## How to calculate rwin

I would like to optimize a line adsl 256bps. I do not know my rwin caluculer. my MTU is 1460 and the ping is 200 ms. How to calculate rwin ?  Reply With Quote

2. Member
Join Date
Feb 2009
Posts
20

## Re: How to calculate rwin

My MTU = 1500 (be 1472 plus 28 after verification by ping)
Corresponding MSS = MTU-40 = 1460
Multiplication by a factor whose value is 44 which gives: 64240
This value is less than 65535, as the maximum value.
Then we must multiply by 2 * 2 or 4 which produces: 64240 * 4 = 256960  Reply With Quote

3. Member
Join Date
Dec 2008
Posts
86

## Re: How to calculate rwin

Now that we know the MTU value, we must know the MSS value, this value will allow us to set the RWIN value. For this is simple:
MSS = MTU - 40 (IP header) which gives 1460 - 40 = 1420 (MSS).

For best results, RWIN should be a multiple of MSS (Maximum Segment Size).
Calculating the value:
MSS x 44 = (value below 65535) x 2 = x2 Value TcpWindowSize or GlobalMaxTcpWindowSize
This gives for our example:
1420 X 44 = 62,480 x2 x2 = 249920  Reply With Quote

4. Member
Join Date
Dec 2008
Posts
105

## Re: How to calculate rwin

The values found in the software chosen by PC Tips (TweakDun) before changes are the proper TTL (or 128), the proper MTU (ie 1500), but the RWIN is 371250. If one accepts that the proper RWIN is not too far from the default, it seems that the calculation of Zebulon is the one to choose.  Reply With Quote

calculate, mtu, rwin 