About high-speed TCP
High-speed TCP (HS-TCP) is designed for high-bandwidth, high-latency networks (also known as long fat networks, or LFNs). It optimizes connections by accelerating traffic over WAN links with large bandwidth but high latency. HS-TCP is automatically activated when the Bandwidth Delay Product (BDP) exceeds 100 packets.
To calculate the BDP and determine if HS-TCP should be enabled, use this formula to calculate the WAN buffer size:
buffer size in bytes = 2 * bandwidth (in bits per sec) * delay (in sec) / 8 (bits per byte)
If the calculated number is greater than the default (256 KB), enable HS-TCP with the correct buffer size. For a link of 155 Mbps and 100 ms round-trip delay:
• Bandwidth = 155 Mbps = 155000000 bps
• Delay = 100 ms = 0.1 sec
• BDP = 155 000 000 * 0.1 / 8 = 1937500 bytes
• Buffer size in bytes = 2 * BDP = 2 * 1937500 = 3 875 000 bytes.
To configure high-speed TCP, enable the high speed congestion control algorithm, increase the WAN and LAN buffers, and then enable in-path support.