dpreed at reed.com
dpreed at reed.com
Sun Apr 28 14:52:57 EDT 2013
Actually, using HTTP 1.1 GET that generates a single packet in each direction for a ping is quite reasonable. In fact, it is "better" for measuring actual path latencies, since ICMP pings *could* be discriminated against in a router along the way (in the "old days" people in the routing community suggested that ICMP should be diverted off of the "fast path" to avoid degrading the user experience).
I've been using this technique to measure bufferbloat-induced delays on Phones and Android phones for quite a while. I have a couple of servers that use nginx "status" handlers to generate a short GET response without touching files as my "targets".
Since it depends on HTTP 1.1's re-use of the underlying TCP connection for successive GET commands, it's a bit fragile.
On Sunday, April 28, 2013 10:56am, "Rich Brown" <richb.hanover at gmail.com> said:
> This is indeed a cool hack. I was astonished for a moment, because it was a
> still true.
> Apenwarr's code sends short HTTP queries of the format shown below to each of two
> The Blip tool shows ~60-70ms for the gstatic host, and ~130 msec for the latter.
> Ping times are ~52 msec and 125msec, respectively. These times seem to track
> response times by my eye (no serious analysis) to load both on my primary
> (bloated) router and CeroWrt.
> Still a cool hack.
> HTTP Request & Response for typical blip "ping"
> OPTIONS /generate_204 HTTP/1.1
> Host: gstatic.com
> Connection: keep-alive
> Access-Control-Request-Method: GET
> Origin: http://gfblip.appspot.com
> User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_3) AppleWebKit/537.31
> (KHTML, like Gecko) Chrome/26.0.1410.65 Safari/537.31
> Access-Control-Request-Headers: accept, origin, x-requested-with
> Accept: */*
> Referer: http://gfblip.appspot.com/
> Accept-Encoding: gzip,deflate,sdch
> Accept-Language: en-US,en;q=0.8
> Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
> HTTP/1.1 204 No Content
> Content-Length: 0
> Content-Type: text/html; charset=UTF-8
> Date: Sun, 28 Apr 2013 12:37:17 GMT
> Server: GFE/2.0
> On Apr 26, 2013, at 7:04 PM, Dave Taht <dave.taht at gmail.com> wrote:
> > Apenwarr has developed a really unique tool for seeing latency and
> > http://apenwarr.ca/log/?m=201304#26
> > --
> > Dave Täht
> > Fixing bufferbloat with cerowrt:
> > _______________________________________________
> > Bloat mailing list
> > Bloat at lists.bufferbloat.net
> > https://lists.bufferbloat.net/listinfo/bloat
> Cerowrt-devel mailing list
> Cerowrt-devel at lists.bufferbloat.net
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