[Cerowrt-devel] [Codel] [Bloat] blip: a tool for seeing internet latency with javascript

[Rich Brown]

Folks,

I noted a paradoxical effect using the blip tool and CeroWrt. I wrote it up and included screen shots in:  http://www.bufferbloat.net/issues/430 Here's the text of the note.

Any thoughts?

Rich Brown
Hanover, NH

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CeroWrt 3.8.8-4 doesn't have as big an effect on the apenwarr.ca blip javascript program as I expected. This isn't really a bug report, but I am using this message as an easy way to include screen shots:

Experimental setup #1

- Macbook connected to demo3.intermapper.com, where I executed iperf -s
- Macbook running iperf locally to that server (iperf -c demo3.intermapper.com -i 1 -t 30)
- Macbook running http://apenwarr.ca/log/ connected to primary (bloated) router running DD-WRT from a couple years ago

Result: blip chart times increase during iperf as expected. The response goes from ~120/200 (green/blue, respectively) to ~500msec for both. (see "Test #1 using primary router wireless" image)

Experimental setup #2:

- MacBook is connected to CeroWrt 3.8.8-4 which is connected to LAN side of DD-WRT which then goes to the Internet. 
- Run "iperf -c" as before

Result: the blip chart times seem to exhibit approximately the same behavior, with the same high response times during the iperf transfer. (See "Test #2 using CeroWrt5 wireless" image below)

Observation:

Both charts seem similar - this is counter to my intuition, and counter to my experience using a simple sequence of one-second pings which don't vary much from the baseline in the experimental setup #2.

Hypotheses:

- blip is a cool hack, but a bad test, and doesn't accurately represent the responsiveness of the network. 
- fq_codel as implemented in CeroWrt3.8.8-4 does not handle these "TCP Pings" well/as expected. 
- ???

Any thoughts?

Rich Brown
Hanover, NH