![\"download\"](\"http:\/\/blogs.it.ox.ac.uk\/nexus\/files\/2016\/09\/download.jpg\")
<\/a>“The connection has been lost. Attempting to reconnect to your session\u2026 “<\/p><\/div>\n
In many cases\u00a0this problem is caused by a feature known as\u00a0Auto-Tuning. This is supposed to\u00a0continually adjust TCP\/IP receive window size based on the network conditions at any given moment. But on a less-than-perfect network this can cause time-out issues.<\/p>\n
The TCP receive window size is the maximum amount of incoming\u00a0data that can be buffered at once\u00a0on the receiving side of a connection. The sending host can send only that amount of data before waiting for an acknowledgement and then\u00a0a “receive window” update from the receiving host.<\/p>\n
The TCP\/IP stack nowadays tunes itself with larger default window sizes than it used to. Instead of using a hard-coded default value, TCP automatically adjusts the window size – beneficial\u00a0during bulk data transmission by reducing the number of segments sent with\u00a0large\u00a0amounts\u00a0of data.<\/p>\n
Auto-Tuning continually determines the optimal receive window size by measuring bandwidth delays and the application’s retrieve rate. In an ideal world this means excellent performance even with\u00a0changing network conditions. In the real world this means occasional timeout errors…<\/p>\n
This doesn’t just affect Remote Desktop – some older version of\u00a0Outlook\u00a0used to get error\u00a00x800CCC0F (“The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP).”) for the same reason.<\/p>\n
What can be done?<\/h2>\n
To tweak your\u00a0auto-tune settings:<\/p>\n
Run CMD as an administrator and enter this command:<\/p>\n
netsh interface tcp set global autotuninglevel=restricted<\/code><\/pre>\nIf you later wish to reverse this setting:<\/p>\n
netsh interface tcp set global autotuninglevel=normal<\/pre>\nTo see what you’ve got right now:<\/p>\n
netsh interface tcp show global
\n<\/code><\/p>\nThe permited\u00a0values for the AutoTuningLevel<\/em> parameter are:<\/p>\ndisabled<\/strong>
\nSets the receive window at the default value.
\nhighlyrestricted<\/strong>
\nLets the receive window grow beyond the default value, but does so very conservatively.
\nrestricted<\/strong>
\nLets the receive window grow beyond the default value, but limits such growth in some scenarios.
\nnormal<\/strong>
\nLets the receive window grow to accommodate most scenarios.
\nexperimental<\/strong>
\nLets the receive window grow to accommodate extreme scenarios.<\/p>\nN.B.<\/span><\/strong>\u00a0\u00a0The experimental value may decrease<\/em> performance and\u00a0should only be used for testing.<\/p>\n\u00a0<\/code><\/p>\n","protected":false},"excerpt":{"rendered":"This message was appearing a little too often for my liking: In many cases\u00a0this problem is caused by a feature known as\u00a0Auto-Tuning. This is supposed to\u00a0continually adjust TCP\/IP receive window size based on the network conditions at any given moment. … Continue reading