Just wanted to put this discussion into a summary form. Hoping that I have
learned something. Hoping to help others learn something.
The original question can be generalized to this:
Host_1------Device-------Host_2
Host one is transmitting at 100 mbs and host two can only receive at 10 mbs
The question is "what happens to the excess packets when Device is
overloaded like this?"
S wrote out the following table:
If Device is: what happens is:
Repeater just does what it's told. If the wire is full it is higher
layers
that deal with it
Ethernet CSMA/CD determines what goes onto the wire in the first place.
Collisions will occur. Or bits won't get onto the wire in the first place
because the medium is saturated. Medium MTU effects Host_1 transmission rate
as well.
Token ring possession of the token determines a stations ability to transmit
data. Medium MTU is a factor here as well.
Frame relay if a frame switch is saturated, packets are dropped and FECN's
and BECN's are generated
ATM I believe that the admissions control process limits the acceptance of
cells into the ATM switch. Correct me if I am wrong here.
I find I am a bit shaky on 100VG, X.25 ( like I care, since it isn't on the
Lab any more :-> ), and HDLC
Lastly, the issue the original post raised - a switch.
In the reading of the this thread, and the reading of some of the
references, what I am determining is that if there is some kind of
flow control mechanism, it comes probably in the form of the switch creating
false collisions on the port of the sender, so as to stop it
from overflowing the switch buffers.
The point being that in terms of layer two, the general means of dealing
with too much input and not enough output is still generally speaking,
massive dropping of excess packets, or some limitation of the medium itself
to limit acceptance of new packets onto the medium.
Which is as it should be, I would think.
Any comments? Does this make sense?
Chuck
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Flem
Sent: Thursday, January 11, 2001 9:56 PM
To: Chuck Larrieu
Cc: [EMAIL PROTECTED]
Subject: RE: switch flow control
One of us needs a pair of glasses ;-) I read ;
minimal specification for asymetric flow control
Has to do with flow control.
If you say a device to pause , process the buffers and
then release the pause is indeed a minimal form of
flow control .
I never played with set port flowcontrol so I getting
impressed ....
I loved the old style no buffer , drop packet .
Things are really getting more complex is it not ?
flem
--- Chuck Larrieu <[EMAIL PROTECTED]> wrote:
> Guys, this "pause" frame does not appear to have
> anything whatsoever to do
> with flow control of data transmission. Unless I am
> blind as a bat I am
> reading the link below to be referencing auto
> negotiation of links between
> NIC and switch or any device on a port and switch..
>
> Look, if a switch cannot output data as fast as it
> comes in, and the buffers
> fill, then packets get dropped. Same as with a
> router. or a PC.
>
> Chuck
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]] On Behalf Of Flem
> Sent: Thursday, January 11, 2001 9:17 PM
> To: [EMAIL PROTECTED]
> Cc: [EMAIL PROTECTED]
> Subject: Re: switch flow control
>
> Or ;
>
http://grouper.ieee.org/groups/802/3/z/public/presentations/jan1997/HFpsbits
> .pdf
>
> Written by a cisco guy ... you are rights cisco do
> implement it.
>
> flem
>
>
> --- Chris McCoy <[EMAIL PROTECTED]> wrote:
> > This is true...sorry. I was reading a cisco
> > document
> > on the Cat 6000s where they explained flow control
> > as
> > being 802.3Z flow control. I screwed up...(see
> >
>
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sft_6_1/configgd
> /ether.htm#xtocid170110)
> > Come to think of it...it's called 802.1x
> > (http://www.ieee802.org/1/pages/802.1x.html).
> Cisco
> > supports it with some exceptions (set port
> > flowcontrol).
> >
> > Guhhhh....
> >
> > Chris M.
> >
> > --- Flem <[EMAIL PROTECTED]> wrote:
> > > 802.1Z ? or 802.3z ?
> > > This is gigabit stuff is it not ?
> > >
> > > Is cisco implementing 802.3z on his gigabit
> > > switches ? Don't think so .
> > > Switch will buffer , if no buffer , then drop
> > > packet.
> > >
> > > Do you know what vendor implements pause frames
> ?
> > >
> > >
> > > flem
> > >
> > >
> > > --- Chris McCoy <[EMAIL PROTECTED]> wrote:
> > > >
> > > > 802.1Z or 'pause frames'
> > > >
> > > > Chris M.
> > > >
> > > > --- Flem <[EMAIL PROTECTED]> wrote:
> > > > > Between NIC and switch ?
> > > > > What is the name of this handshaking ?
> > > > >
> > > > >
> > > > > flem
> > > > >
> > > > > --- Circusnuts <[EMAIL PROTECTED]> wrote:
> > > > > > I believe there is a handshake going on
> with
> > > the
> > > > > > switch & NIC
> > > > > >
> > > > > >
> > > > > >
> > > > > > ----- Original Message -----
> > > > > > From: "Rick H
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