發表文章

目前顯示的是 十月 29, 2012的文章

TCP small queues

TCP small queues是另一個減少網絡擁堵的機制,它的目標在於減少xmit queues (qdisc & device queues)中TCP包的數量,來減少RTT和cwnd bias,以此解決部分網絡擁堵情況。我們可以在不降低名義帶寬的情況下,減少每一個批量發送者的緩衝區:每Gbit< 1ms (相比於50ms with TSO)以及每100Mbit < 8ms (相比於132 ms) By Jonathan Corbet
July 17, 2012 The "bufferbloat" problem is the result of excessive buffering in the network stack; it leads to long latencies and poor reliability in the network as a whole. Fixing it is a matter of buffering less data in each system between any two endpoints—a task that sounds simple, but proves to be more challenging than one might expect. It turns out that buffering can show up in many surprising places in the networking stack; tracking all of these places down and fixing them is not always easy.A number of bloat-fighting changes have gone into the kernel over the last year. The CoDel queue management algorithm works to prevent packets from building up in router queues over time. At a much lower level, byte queue limits put a cap on the amount of…

TCP Fast Open: expediting web services

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“Fast Open”是建立TCP鏈接的最優選擇,相比於一般TCP會話能夠減少一個RTT(round time trip),在訪問流行網站時可以提速4%-41%。但這一版本僅加入了客戶端的TFO支持。 By Michael Kerrisk
August 1, 2012 Much of today's Internet traffic takes the form of short TCP data flows that consist of just a few round trips exchanging data segments before the connection is terminated. The prototypical example of this kind of short TCP conversation is the transfer of web pages over the Hypertext Transfer Protocol (HTTP).
The speed of TCP data flows is dependent on two factors: transmission delay (the width of the data pipe) and propagation delay (the time that the data takes to travel from one end of the pipe to the other). Transmission delay is dependent on network bandwidth, which has increased steadily and substantially over the life of the Internet. On the other hand, propagation delay is a function of router latencies, which have not improved to the same extent as network bandwidth, and the speed of light, which has remained stubbornly constant. (At inter…