Hi,
I don't know if my input got through on Friday or when ever.
I understand there is a clocking type pulse that exists between the port and the nic.
If this does not match then you will get no link and therefore no comms. In a
nutshell a 100Meg port will not see a 10 Meg port.
OK so we get to Autonegotiate. This works in a similar manner to a modem retrain and
will attempt to train to the best and/or a preset speed. Unfortunately not all
manufacturers agree on how this is to be acheived and therefore autoneg is not always
a good option. Some devices do not correctly identify hard set ports.
Just a thought. A clocking type pulse sets up the link, once the link is up then
comms can take place.
Teunis,
Hobart, Tasmania
Australia
On Saturday, January 13, 2001 at 06:06:58 PM, Chuck Larrieu wrote:
> 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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