Re: Reg: Quality of Service routing

[Qingming Ma <[e-mail]>]

I agree with Roch. Router packet pool memory and CPU cycles can often
become bottleneck in certain scenarios, especially when packet
forwarding 
is done by software. One probably should never expect that there are 
sufficient memory and CPU cycles, since keeping adding new QoS features 
(e.g., classifying, scheduling, admission, reservation, policy
enforcing, 
access control, ...) will consume more and more CPU resources.   

Let us assume that router CPU is never the bottleneck. Even with
sufficient
large amount of bandwidth, we may still need QoS routing, unless one
can ensure that the traffic load is always below the link capacity and 
the network rarely gets congested. One common belief is that QoS is only
needed when the load of QoS traffic is heavy, so that we can reduce the
number of requests being blocked. However, QoS routing is still useful 
even when the QoS traffic load is light. For example, when the load of 
best effort traffic is heavy and conentrated on some hot links, although 
call blocking rate for QoS traffic is not an issue, but encourage QoS
traffic 
to use the links with relatively light load of best effort traffic can 
improve over all throughput for best effort traffic.   

Qingming

Roch Guerin wrote:
> 
> Raghu V.V.J Vadapalli wrote:
> 
> > Dear All,
> >
> > I have one basic question regarding QoS routing.
> >
> > Do we need QoS routing if we have enough infinite (I mean
> > large ) bandwidth.
> >
> > >From my poor knowledge:
> >
> > We need QoS routing b'cos we have limited BW and we want
> > to give priority to QoS flows. If some one comes with
> > a Tx system which supports 100s Gb/s,(say 128 channel WDM system)
> > Do we need to support the "special"  status for the QoS flows.
> > May in that case the memory at the routers will be
> > bottleneck.
> 
> Besides the delay issue that Tony mentions, you should also consider
> that tx bandwidth is not the only resource inolved in delivering your
> data.  You also need switches/routers that can keep up with the
> bandwidth, and if they don't they are the resource you need to focus on,
> i.e., you need to consider the forwarding tput available rather than
> just the raw bandwidth.
> 
> Roch
> 
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