Start Me Up: Determining and Sharing TCP's Initial Congestion Window

When multiple TCP connections are used between the same host pair, they often share a common bottleneck -- especially when they are encapsulated together, e.g. in VPN scenarios. Then, all connections after the first should not have to guess the right initial value for the congestion window, but rather get the appropriate value from other connections. This allows short flows to complete much faster -- but it can also lead to large bursts that cause problems on their own. Prior work used timer-based pacing methods to alleviate this problem; we introduce a new algorithm that ``paces'' packets by instead correctly maintaining the ACK clock, and show its positive impact in combination with a previously presented congestion coupling algorithm.