Date: Sun, 11 Mar 2001 18:17:20 -0800 (PST) From: Tom Samplonius <tom@sdf.com> To: Alex Huppenthal <alex@aspenworks.com> Cc: freebsd-isp@FreeBSD.ORG Subject: Re: ATM and traffic shaping Message-ID: <Pine.BSF.4.05.10103111806400.9461-100000@misery.sdf.com> In-Reply-To: <004101c0aa73$4bdefdc0$1800a8c0@d7k>
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On Sun, 11 Mar 2001, Alex Huppenthal wrote:
> It turns out that traffic shaping for ATM means being able to delay each
> cell to a specific egress ('transmit' in english) rate.
Yes, exactly. And many switches are configured to drop non-conforming
cells (cells that exceed the allowable cell-per-second rate). I wouldn't
recommend that anyone attempt ATM without understanding all the service
categories and parameters.
However, it somewhat depends on the category of service that you
receive. There are lots of possibilities: ubr, cbr, rt-vbr, nrt-vbr, and
vbr. The maximum cell rate isn't always a simple thing, as they interact
with the mcr, pcr, mbs, and scr parameters.
Since you are using your own ATM switch, I'm surprised that you can't
let your switch buffer cells for you, rather than discard them. For
instance, if your ATM provider has given you a cbr service with 10K
cells/second rate, just let FreeBSD run ubr into the switch.
But it really depends on your ATM service provider. I have a very
expensive switch with an ATM card and multiple ethernet ports. My ATM
service provider is providing an abr with a pcr of 10Mbps service. Their
switch will buffer and pace out traffic for me, so I have the link setup
as ubr on my end. In fact, it was the configuration they recommended.
Tom
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