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Re: [Diffserv] Model - queues - replacement text



Linsong 
> 
> > 
> > 7.  Queues
> > Queues order the transmission of packets belonging to the different traffic
> > streams, possibly storing them temporarily or discarding them. Packets are
> > usually stored either because there is a resource constraint (e.g.,
> > available bandwidth) which prevents immediate forwarding, or because the
> > queue is being used to alter the temporal properties of a traffic stream.....
> >
> > 
> > 7.1  Model
> > Queuing is a function a which lends itself to innovation.  It must be
> > modelled to allow a broad range of possible implementations to be
> > represented using common structures and parameters.  This model uses
> > functional decomposition as a tool to permit the needed lattitude.  
> > 
> > Queues perform three distinct, but related, functions:  they store packets,
> > they modulate the departure of packets belonging to various traffic streams
> > and they selectively discard packets.  This model decomposes queues into the
> > component elements that perform each of these functions.  These elements
> > which may be connected together either dynamically or statically to
> > construct queueing subsystems.  A queue is thus composed of of one or more
> > FIFO, one or more scheduler, and one or more discarder.  See figure TBA for
> > an example of a queue.  
> > 
> 
> I don't quite catch the meaning of the word "order" in the first sentence.
> It seems to me that the Queues per se are just buffers.
This gets to Grenville's issue.  Maybe queueing system is better.
> It is the queueing functions that can "order" (or modulate as said in 7.1) the transmission of packets while enqueueing the packets. 
> It reads much as if queues are the same as queueing functions. 
> 
> But, it again reads:
> > construct queueing subsystems.  A queue is thus composed of of one or more
> > FIFO, one or more scheduler, and one or more discarder.  See figure TBA for
> > an example of a queue.  
> > 
> meaning the queues are "FIFO-ordered buffer" subject to discarding and scheduling.
> Shouldn't a queueing system include a set buffers(queues) and queueing disciplines such as FIFO, a mean of storingpackets, Scheduler, of transmitting packets, and discarder, of dropping packets.
> ..Maybe I misunderstood.
> 
>  
> > (i.e., shaping).  Packets are discarded either because of buffering
> > limitations or as a feedback control signal to reactive control protocols
> > such as TCP.
> 
> Also, shouldn't packets be discarded if they either are out of (by metering) or cannot be shaped into (shaping fails) the specific temporal properties of a traffic stream, in addition tobuffering limitations and feedback controls.
> 
That's a specific case of a buffering limitation, but an important one. I'll 
call it out separately.

Dan


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