jg at freedesktop.org
Sun Apr 28 20:37:04 EDT 2013
On Sun, Apr 28, 2013 at 2:52 PM, <dpreed at reed.com> wrote:
> 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).
Yes, using HTTP is good in this respect. I worked with the author of
httping to get support for persistent connections 18 months or so ago.
How to deal with proxies is one question, though one should mark the
response uncachable. (unless the intent is to just test the path as far as
In practice, I've never seen signs of ICMP being put off the fast path in
my testing; this doesn't mean it doesn't happen.
> 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.
I don't think this should be particularly fragile, unless you know
something I don't.
> both TCP and DNS protocols from the browser, so if you play cards right,
> you can cause single TCP exchanges and single UDP exchanges to happen with
> cooperative servers (web servers using HTTP 1.1 and DNS resolvers using
> uncacheable UDP name lookups).
> On Sunday, April 28, 2013 10:56am, "Rich Brown" <richb.hanover at gmail.com>
> > This is indeed a cool hack. I was astonished for a moment, because it
> was a
> that is
> > still true.
> > Apenwarr's code sends short HTTP queries of the format shown below to
> each of two
> > hosts:
> > http://gstatic.com/generate_204
> > http://apenwarr.ca/blip/
> > The Blip tool shows ~60-70ms for the gstatic host, and ~130 msec for the
> > Ping times are ~52 msec and 125msec, respectively. These times seem to
> > response times by my eye (no serious analysis) to load both on my primary
> > (bloated) router and CeroWrt.
> > Still a cool hack.
> > Rich
> > -------------------------
> > 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)
> > (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:
> > http://www.teklibre.com/cerowrt/subscribe.html
> > > _______________________________________________
> > > Bloat mailing list
> > > Bloat at lists.bufferbloat.net
> > > https://lists.bufferbloat.net/listinfo/bloat
> > _______________________________________________
> > Cerowrt-devel mailing list
> > Cerowrt-devel at lists.bufferbloat.net
> > https://lists.bufferbloat.net/listinfo/cerowrt-devel
> Codel mailing list
> Codel at lists.bufferbloat.net
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