Re: [LARTC] SFQ improvement ideas

[Martin Devera <devik@cdi.cz>]

>  > either sorted queues (log N) or cycle on head of queue until all
>  > expired ones are deleted. But it doesn't preserve fairnes IMHO.
>  > In any way I'll think about it :)
> You're thinking of removing a packet when it has been in the queue too
> long.  I'm thinking of something much easier.  When you dequeue just
> check to see it's not too old.  If it is then discard it and go on to
> the next one.  I admit that this could result in a large amount of
> work for one packet dequeued, but that work translates into much more
> time saved by not sending old packets.

It is exactly what I meant by "cycle on head of queue". But
compare it with queue depth limiting. When you know rate and depth
you can compute the oldest packet on the queue. So that it will
assure the same for you but with less of work and less of storage
(packets are dropped at enqueue). 
 
>  > it is better determined by bytes send. Hi-load traffic is for
>  > example long ftp download.. I'm not sure how to detect them yet.
>  > See www.cisco.com, IOS documentation, QoS section.
> I have looked there.  Perhaps we simply interpret the contents
> differently.  

Maybe :) How do you interpret it ?
 
>  > >  > Nice effect is that short conversations are handled faster
>  > >  > and long downloads are isolated with lower priority.
>  > > Isn't this just what you get from a queue for each flow?
>  > > I thought that's what WFQ did.
>  > 
>  > No. For flows A,B,C,X where X is interactive one the nornal SFQ 
>  > schedule is: ABCDXABCDX.... and WFQ is AXBXCXAXBXCX.... Thus lower
>  > delay.
> (Except for the D's I guess.)
> Again, where do you see this?  I've not seen anything in Cisco doc
> that says this.

I quote: 
(http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/113ed_cr/fun_c/fcprt4/fcperfrm.htm#xtocid128886)
------
Weighted fair queueing can manage duplex data streams, such as those
between pairs of applications, and simplex data streams such as voice
or video. From the perspective of weighted fair queueing, there are two
categories of data streams: high-bandwidth sessions and low-bandwidth
sessions. Low-bandwidth traffic has effective priority over high-bandwidth
traffic, and high-bandwidth traffic shares the transmission service
proportionally according to assigned weights. 
------

devik

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