On 6 Feb 2015, at 16:57, Michael Richardson wrote:
Jim Gettys <jg(_at_)freedesktop(_dot_)org> wrote:
What effect does this algorithm have in practice? Here are some examples:
o real time isochronous traffic (such as VOIP, skype, etc) won't build
a queue, so will be scheduled in preference to your bulk data.
o your DNS traffic will be prioritized.
o your TCP open handshakes will be prioritized
o your DHCP & RA handshakes will be prioritized
o your handshakes for TLS will be prioritized
o any simple request/response protocol with small messages.
o the first packet or so of a TCP transfer will be prioritized: remember,
that packet may have the size information needed for web page layout in it.
o There is a *positive* incentive for flows to pace their traffic (i.e.
to be a good network citizen, rather than always transmitting at line rate).
*All without needing any explicit classification. No identification of
what application is running is being performed at all in this algorithm.*
This last part is I think the part that needs to be shouted at residential
ISPs on a regular basis. I wish that the IETF and ISOC was better able to
do this... in particular to ISPs which do not tend to send the right people
to NANOG/RIPE/etc.
Explicit class-based queueing is seeing fairly substantial deployment in some
places - such as the UK - where for a few years now the default home routers
(Thomson/Technicolor TG587/582 etc) for a number of the big ISPs (Plusnet,
O2/Sky, Talk-talk and others) have shipped preconfigured with 5 queuing classes
that classify traffic and provide for differing treatment. They also have some
ALGs that work with SIP/H.323. I'm not aware of AQM enabled on the individual
queues but at least they separate the traffic into different queues - albeit
based on port number or ALG classifiers. Better than nothing anyway.
Also the DOCSIS3.1 standard now mandates the use an AQM - namely PIE, though
others can be implemented. I'm not sure where that is in terms of deployment
though. There's a good report on it here:
http://www.cablelabs.com/wp-content/uploads/2013/11/Active_Queue_Management_Algorithms_DOCSIS_3_0.pdf
Piers
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