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Patches for the Linux TCP stack
In the following you will find some patches for the vanilla Linux kernel TCP stack.
Internet-Draft: Make TCP more Robust to Long Connectivity Disruptions
Disruptions in end-to-end path connectivity which last longer than one retransmission timeout cause suboptimal TCP performance. The reason for the performance degradation is that TCP interprets segment loss induced by connectivity disruptions as a sign of congestion, resulting in repeated backoffs of the retransmission timer. This leads in turn to a deferred detection of the re-establishment of the connection since TCP waits until the next retransmission timeout occurs before attempting the retransmission.
This document describes how standard ICMP messages can be exploited to disambiguate true congestion loss from non-congestion loss caused by long connectivity disruptions. Moreover, a revert strategy of the retransmission timer is specified that enables a more prompt detection of whether the connectivity to a previously disconnected peer node has been restored or not. The specified algorithm is a TCP sender-only modification that effectively improves TCP performance in presence of connectivity disruptions.
RFC 4653 - Improving the Robustness of TCP to Non-Congestion Events
This document specifies Non-Congestion Robustness (NCR) for TCP. In the absence of explicit congestion notification from the network, TCP uses loss as an indication of congestion. One of the ways TCP detects loss is using the arrival of three duplicate acknowledgments. However, this heuristic is not always correct, notably in the case when network paths reorder segments (for whatever reason), resulting in degraded performance. TCP-NCR is designed to mitigate this degraded performance by increasing the number of duplicate acknowledgments required to trigger loss recovery, based on the current state of the connection, in an effort to better disambiguate true segment loss from segment reordering. This document specifies the changes to TCP, as well as the costs and benefits of these modifications.
This patch adds TCP-NCR as socket option to the Linux kernel. To use TCP-NCR in careful mode (resp. aggressive mode), an application has to set the TCP-NCR socket option (23) to the value 1 (resp. 2) when it starts a TCP connection.
