Re: OT - End-to-End QoS Network Design - Second Eddiont RANT

Hi Dave,

I agree with John here, adding buffering can reduce interpacket delay
variation, particularly useful for circuit over packet and voice but
possibly your concern is with bufferbloat which is a different beast as to
what appears being discussed

The point of the playout or dejitter buffer is to help build some
determinatistic delay for the services which are travelling on a
connectionless environment, allowing you to pace out the data on network
egress at the expected service bit rate hopefully not getting buffer
underruns (or in some cases overruns) - these buffers are something you
typically place at each end of the service termination though, not at each
network hop since they are concerned with individual services rather than
macroflow behaviour. These values usually made as small as practically
possible but some headroom is needed to handle network disruptions.

I cant say I know the particular book you are reading but usually early on
general concepts are discussed and then get fleshed out in more detail as
you go through, possibly talking about areas most people can directly
influence first and perhaps get quick wins if there are problems and then
discuss more detailed behaviours and when the first introduced concepts
aren't necessarily a one size fits all.

Cheers,
Adam

On Sun, Jun 8, 2014 at 12:54 AM, John Neiberger <jneiberger_at_gmail.com>
wrote:

> b Buffering does reduce jitter. It also increases latency, but has the
> benefit of smoothing out variable latency. It's a trade-off. In the VoIP
> world, that's why you have a dejitter buffer. It smooths out small
> variations in delay, but adds overall delay. The trick is finding the
> balance that solves your problem but doesn't make people feel like they're
> on a satellite link. b
>
>
> On Fri, Jun 6, 2014 at 1:59 PM, Dave Serra <maybeedave_at_yahoo.com> wrote:
>
> > B
> > I just cracked open the b End-to-End QoS Network Designb
> > Second Edition
> > book expecting to really hone in my understanding of QoS and
> > right on the
> > first page the author makes the following statement b streaming
> > video
> > (unbidirectional flows that benefited from both network and application
> > level
> > buffering to offset variations in transmission delays)b B We know
> > b variations in transmission delaysb
> > to be jitter.B Why is this CCIE
> > telling
> > me that network buffering reduces jitter when we know it is going to
> > INCREASE
> > jitter.B Ib m sure some willB rationalize
> > corner cases where jitter
> > can be improved by network buffering but in the
> > statistical random switching
> > world where flows come into and out of existence
> > the variance will
> > certainlyB be high.
> > So now Ib m left wondering if I should just put this book
> > down and consider its cost a donation to ciscopress?B Its only the first
> > page
> > and I am very
> > unimpressed.B
> > Make a small loan, Make a big difference -
> > Kiva.org
> >
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Received on Sun Jun 08 2014 - 10:20:10 ART