802.3x Ethernet flow control in VoIP

Roger Smith

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Apr 15, 2003, 1:14:27 AM4/15/03

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Hi,

Some vendors recommend to disable Ethernet flow control (802.3x) on FDX
uplink ports when you want to run IP Telephony on your data network.

Q. Can somebody explain to me why ? And what is the impact of not doing it
when QoS is configured and VoIP is given the highest priority ? And what
exactly would trigger a pause frame to be sent ?

Many thanks,

Roger

Manfred Kwiatkowski

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Apr 15, 2003, 4:25:46 AM4/15/03

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In article <TyMma.11251$EK2.3...@wagner.videotron.net>,

"Roger Smith" <RSm...@Netdesign.com> writes:
>
>Some vendors recommend to disable Ethernet flow control (802.3x) on FDX
>uplink ports when you want to run IP Telephony on your data network.

I would recommend to disable Ethernet flow control in any case.

>
>Q. Can somebody explain to me why ? And what is the impact of not doing it

>when QoS is configured and VoIP is given the highest priority ?i

Your conversation will be delayed for reasons you were trying to avoid
by priorization in the first place.

--
Manfred Kwiatkowski kwiat...@zrz.tu-berlin.de

eMail2Me

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Apr 15, 2003, 10:09:15 AM4/15/03

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Roger Smith wrote:

> Hi,
>
> Some vendors recommend to disable Ethernet flow control (802.3x) on FDX
> uplink ports when you want to run IP Telephony on your data network.
>
> Q. Can somebody explain to me why ? And what is the impact of not doing
> it
> when QoS is configured and VoIP is given the highest priority ? And what
> exactly would trigger a pause frame to be sent ?
>
> Many thanks,
>
> Roger

How do you disable the ethernet flow control on FDX uplink ports? Do you
just disable those ports or do you disable all the flow control ports? BTW,
what constitutes to the ethernet flow control?

eMail2Me

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Apr 15, 2003, 10:09:36 AM4/15/03

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Roger Smith wrote:

> Hi,
>
> Some vendors recommend to disable Ethernet flow control (802.3x) on FDX
> uplink ports when you want to run IP Telephony on your data network.
>
> Q. Can somebody explain to me why ? And what is the impact of not doing
> it
> when QoS is configured and VoIP is given the highest priority ? And what
> exactly would trigger a pause frame to be sent ?
>
> Many thanks,
>
> Roger

How do you disable the ethernet flow control on FDX uplink ports? Do you

Albert Manfredi

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Apr 15, 2003, 11:15:35 AM4/15/03

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Flow control is used in full duplex mode to hold back data from a
source (either host or switch), if the downstream device is about to
overflow its buffer. It in effect takes the place of the CSMA/CD
protocol, although it's not the wire that gets busy here, it's the
downstream device.

VoIP or other streaming media applications cannot function properly
if their voice samples are held back. Better drop a few than create
a queue, and mess up the timing between samples.

Ideally, the VoIP frames would be few and far between, compared to
data frames, and the VoIP frames would be given higher priority than
time-insensitive data frames, at switches and hosts.

Bert