[c-nsp] difference between "bandwidth" and "priority" commandinpolicy

[Jeff Tantsura]

Hi,

It is also important to understand the difference between 
loose and strict policers for priority queue

See inline


> [1] this can either be configured as:
> 
> class X
>  priority <bandwidth>

Here you'd police only in case of congestion 

> or
> 
> class X
>  priority
>  police rate <bandwidth>
>
While here you'd police when you'd hit the specified rate

Cheers,
Jeff
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
> bounces at puck.nether.net] On Behalf Of Pelle
> Sent: donderdag 5 juni 2008 9:45
> To: Ziv Leyes
> Cc: cisco-nsp
> Subject: Re: [c-nsp] difference between "bandwidth" and "priority"
> commandinpolicy
> 
> > When I say this link will have this bandwidth it sounds to me like it's
> a dedicated bandwidth that limits the link to the given value.
> > When I say priority I think of a link with several clients where one of
> them gets priority over the others, but in case there are no others it can
> get more.
> 
> it's not about clients, but queues. technically there is no problem
> putting one client in the priority queue and others in normal queues,
> but that's not the intention behind qos. it's all about applications
> with different needs (bandwidth, jitter, drop probabilities etc).
> 
> a longer explanation than olivers is:
> 
> a class with priority will have a strict priority queue, i.e. traffic
> in this queue will be serviced before all other queues. this also
> means that a priority queue can starve other queues, so it's important
> to limit the traffic in the queue. that is done by a policer[1] which
> sets a *maximum* bandwidth for the queue.
> 
> a class with a bandwidth statement is given a *minimum* guarantee for
> the traffic in the queue.
> 
> if one or more queues don't use the allocated bandwidth, the excess
> bandwidth is shared among the other "bandwidth" queues, either in the
> same proportion as the configured bandwidth or the configured
> "bandwidth remaining".
> 
> in essence:
> * priority <bw> gives a strict priority queue with a *maximum* bw
> guarantee
> * bandwidth <bw> gives a queue with a *minimum* bw guarantee
> 
> 
> 
> --
> Pelle
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