TCP Window Size Scaling

Hi Zaman,

Originally the window size is a 16 bit value so the largest window size would be 65535. We couldn’t add more bits to the TCP header but it was possible to reassign the purpose of those 16 bits.

What we do nowadays is that we use a scaling factor so that we can use higher window sizes.

For example, the window size value is 400 and the scaling factor is 64.

400 x 64 = 25600

In my lesson one of the screenshots also showed a windows size of 132480.

Window size value = 2070
Window size scaling factor = 64

2070 x 64 = 132480

Here’s a short explanation of the relative sequence and ACK numbers:

TCP Header explained

Rene

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