[R-C] LEDBAT vs RTCWeb

[Harald Alvestrand]

On 04/11/2012 12:43 PM, Jim Gettys wrote:
> On 04/11/2012 02:16 AM, Harald Alvestrand wrote:
>> On 04/10/2012 09:14 PM, Jim Gettys wrote:
>>> On 04/10/2012 02:58 PM, Randell Jesup wrote:
>>>> 100ms is just bad, bad, bad for VoIP on the same links.  The only case
>>>> where I'd say it's ok is where it knows it's competing with
>>>> significant TCP flows.  If it reverted to 0 queuing delay or close
>>>> when the channel is not saturated by TCP, then we might be ok (not
>>>> sure).  But I don't think it does that.
>>>>
>>> You aren't going to see delay under saturating load under 100ms unless
>>> the bottleneck link is running a working AQM; that's the property of
>>> tail drop, and the "rule of thumb" for sizing buffers has been of order
>>> 100ms.  This is to ensure maximum bandwidth over continental paths of a
>>> single TCP flow.
>>>
>>> Unfortunately, the bloat in the broadband edge is often/usually much,
>>> much higher than this, being best measured in seconds :-(.
>>> http://gettys.files.wordpress.com/2010/12/uplink_buffer_all.png
>>> http://gettys.files.wordpress.com/2010/12/downlink_buffer_all.png
>>> (thanks to the Netalyzr folks).
>> the encouraging thing in those (depressing) charts is that the fiber
>> stuff (green subcloud) seems to be less broken than the DSL. So the
>> future may actually be less depressing than the past.
> Get out your anti-depressants.  The ICSI data *understates* the severity
> of the problem.
>
> The ICSI data tops out at 20Mbps due to a limitation in their server
> systems, so we don't really know how good/bad fiber is (since most fiber
> tiers of service start around 20Mbps and so won't show up where it
> should on that plot).
>
> Secondly, the home router situation is even worse than broadband.  As
> soon as the bandwidth is higher in the broadband hop than the wireless
> hop (and 802.11g tops out at about 20-22Mbps), the bottleneck shifts to
> the wireless hop, and you have the problem on either side of the
> wireless hop (our OS's and home routers).  This is why I spend my time
> on home routers and Linux.  Home routers/our operating systems have yet
> more bloat than broadband, typically.
>
> We have a disaster on our hands.
>
> Sorry to be the bearer of such horrifying news.
I know - well enough to want to smile at any small hint of a silver 
lining :-)