Last Mile QoS WAS: RE: QOS or more bandwidth

Wayne Bouchard web at
Tue May 29 20:09:20 UTC 2001

On Tue, May 29, 2001 at 03:39:40PM -0400, Nathan Stratton wrote:
> On Tue, 29 May 2001, Pete Kruckenberg wrote:
> > A 1536-byte frame has a fairly significant impact (~8ms) at
> > 1.5Mb/s. QoS appears to have diminishing return as you move
> > beyond 45Mbps, at least as far as multi-service networks go.
> > Maybe QoS isn't necessary or useful in the core if you have
> > line-speed switching and no congestion on an OC-X/DWDM
> > network.
> It has even a larger impact on a 128K frac T1 (~93ms). QoS is a big help,
> but at slower speeds you also need to deal with fragmentation and the
> layer 2 transport. I am surprised that there has been so little movement
> as far as QoS and efficiency in regards to VoIP. Take a standard voice call
> using G.726 at 32 kbps, you get 40 bytes of voice every 10 ms. Now add on
> your 20 byte IP header, 8 bytes UDP, and 12 byte RTP header. So now we are
> at 80 bytes and most of the time we are shoving this on ATM so our 32K
> voice stream now sucks 84.8 kbps.
> If you are interested in more info on QoS and Voice/Data over last mine
> networks check out my website:

Adding control through layering has been something of a pet peeve of
mine for quite a while (especially when ATM is involved in the mix and
now with MPLS, it just gets a tad worse). As Nathan has demonstrated,
usually added overhead just means added headaches. It seems to me that
there ought to be better ways to go about this whole thing.


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