I was going through some TCP windowing over a high speed WAN link, and thought it might be worth to post some info regarding this.
We do face a typical problem of having slow speed file transfer even if the dedicated pipe is capable of supporting it.
There are three factors which affects this…
- TCP Window Size.
- Round trip latency of the circuit.
- Bandwidth of the circuit.
Maximum throughput you can get from a line with 10ms latency and a TCP window of 32KB can be calculated with…
32KB –> 32 x 1024 x 8 = 262144 Bits
262144 ÷ 0.01 = 26214400 bps = 26.2144 Mbps
Let’s say we have an OC-3 line, which is at 155 Mbps and a round trip latency of 10ms, and we need to calculate the TCP window size to maximize the throughput…
155.52 x 106 = 155520000 bps
TCP_WINDOW = 155520000 x 0.01 = 1555200 Bits = 194400 Bytes = 189.84375 KB
Hope I got the calculation right 🙂