Google 研發出的 BBR: Congestion-Based Congestion Control

Google 針對 TCP 的 congestion control 研究出了新的方法,是個純 sender-side 的演匴法,可以讓現有的 internet 直接換上去使用:「[net-next,14/14] tcp_bbr: add BBR congestion control」。

在 long-lived TCP connection 愈來愈普及後 (像是 HTTP/2),TCP 連線的最佳化可以用統計模型來計算,這也就是 BBR 的想法:

In a nutshell, BBR creates an explicit model of the network pipe by sequentially probing the bottleneck bandwidth and RTT. On the arrival of each ACK, BBR derives the current delivery rate of the last round trip, and feeds it through a windowed max-filter to estimate the bottleneck bandwidth. Conversely it uses a windowed min-filter to estimate the round trip propagation delay. The max-filtered bandwidth and min-filtered RTT estimates form BBR's model of the network pipe.

不過 QUIC 不是也開始有進展了嗎?(參考「Google Chrome 52 預設開啟了更快的 QUIC (被戲稱為 TCP/2)」這篇)

感覺 QUIC 解決的比較徹底,不過 443/udp 的 firewall 問題的確也是個需要時間解決的課題...

前幾天 Gmail 收信延遲的問題...

前幾天 Gmail 可以正常運作,但一直收不到信的問題由官方發公告出來解釋了:「More On Gmail’s Delivery Delays」。

官方宣稱,這次的問題出自於兩個獨立的網路同時掛掉,造成 Gmail 的收信處理能力大幅下降:

The message delivery delays were triggered by a dual network failure. This is a very rare event in which two separate, redundant network paths both stop working at the same time. The two network failures were unrelated, but in combination they reduced Gmail’s capacity to deliver messages to users, and beginning at 5:54 a.m. PST messages started piling up.

最後是十個多小時後完全恢復。