[mythtv-users] UK users - more Freeview services becoming available
linux at thehobsons.co.uk
Wed Sep 7 09:01:59 UTC 2011
Nicolas WILL wrote:
>Just a word on QoS...
>QoS needs to be rolled out end to end.
>It cannot be just set on just one of the ends, your end. What's the
>point on applying QoS rules on the receiving end, where you will drop
>packets *after* they have come to you anyway?
Actually, you can achieve quite a good approximation.
If you drop packets in a TCP stream then that triggers congestion
avoidance at the sender - ie it will slow down. So talking the
example under discussion, if we drop packets on the video stream
(assuming it's a file transfer via TCP) then that will trigger the
sender to slow down.
As long as you can keep the overall flow rate below the rate at which
router buffers start building up, then that makes a dramatic
improvement to latency - with improvements to time sensitive traffic
like VoIP & gaming, and improvements to the "feel" of interactive
traffic like browsing.
The biggest problem you face on a home connection is that you don't
have a fixed speed to throttle against. At work we have a (very
expensive) uncontended, unthrottled bit pipe delivered over fibre. At
home, almost all of us get a variable bit rate which means you don't
have a sensible target to throttle against.
As an example, one of our customers is (quite literally) a stones
throw from their exchange and get the full 8M down/800k up sync rate.
However, speed tests turned in between 1M and 1.5M down at peak times
So if you tried to use QoS, you'd need to throttle down to about 1M
to have it work all the time !
>However, rolling out end to end QoS with users in charge of their own
>little rules is quite an impossible thing to roll out! The first thing
>you establish when thinking about QoS policies, as a network operator,
>is the trust border: the network boundary where you will stop honouring
>user-set QoS flags and replace them with your own...
The one thing you can guarantee is that if the ISP honoured user-set
QoS then some *tards would set it on peer-peer filesharing traffic
and f**k it up for everyone.
There is one ISP that does offer QoS end-end. Provided you are on an
exchange where their partner has their own equipment, then they can
offer QoS end-end to Gradwell's servers for VoIP. That's only for
VoIP, and only to their servers.
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