At 11:03 AM 1/30/01, Thangavel .V.M wrote:
>I have a question extending to this discussion, whether this early token
>release will create a bus contention ?
It won't create bus contention since Token Ring is not a bus. But it can
reduce the amount of time a station has to wait for a free token, so you
could say it reduces contention. You may be thinking that it makes it more
likely that another station will jump in and grab the token, but that
station probably would have grabbed the token anyway. Estimating how much
early token release helps or harms is a really tricky problem that would
require detailed knowledge of traffic arrival patterns, which is often
impossible to determine.
Without early token release, a station releases a free token only after the
station's transmission has completely circled the ring and returned to the
sender. With early token release, the station releases a free token right
after sending the last bit of the transmission. On large networks, this may
reduce access time for other stations. On small networks, it doesn't make
any difference because the transmission has come around already anyway.
That's the dirty little secret with early token release (it doesn't really
help on most networks! &;-)
And here's another dirty little secret. You know those frame-copied bits
that everyone makes a big deal about? Well, IBM developed Token Ring with
two types of delivery mechanisms -- best effort (in which case the bits are
ignored) and assured delivery (in which case the bits are checked). As it
turns out almost all applications are best effort and the bits are ignored.
The frame copied bits are used for ring poll and neighbor discovery. When
the Active Monitor sends Active Monitor Present, the immediately downstream
neighbor sets the Frame Copied/Address Recognized bits and retransmits the
frame. The rest of the stations simply retransmit the frame. They now know
that there's an Active Monitor, but only the first station knows who its
upstream neighbor is. That station then sends Standby Monitor Present. The
immediately downstream neighbor sets the Frame Copied/Address Recognized
bits and retransmits the frame. That station now knows who its upstream
neighbor is. And so it continues until every station learns the address of
its upstream neighbor, using the Frame Copied/Address Recognized bits. And
that's what they are really good for. They aren't good for acks.
Priscilla
>Thanks / Thangavel
>----- Original Message -----
>From: "Richard Gallagher" <[EMAIL PROTECTED]>
>To: "Jim Dixon" <[EMAIL PROTECTED]>; "Nathan Casassa"
><[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
>Sent: Monday, January 29, 2001 8:52 PM
>Subject: Re: Early Token release
>
>
> > >From CCO:
> >
> > "Early token release is a method whereby the Token Ring interfaces can
>release
> > the token back onto the ring immediately after transmitting, rather than
> > waiting for the frame to return"
> >
> > Therefore you do not need to wait for the frame to return to see if the
>frame
> > has been copied or not (frame status field) and then removed from the
>ring.
> >
> > On Jan 29, 4:17pm, Jim Dixon wrote:
> > > Subject: RE: Early Token release
> > > I thought that Early Token Release was when the Token was released prior
>to
> > > acknoledgement being received?
> > >
> > >
> > > -----Original Message-----
> > > From: Nathan Casassa [mailto:[EMAIL PROTECTED]]
> > > Sent: Saturday, January 27, 2001 12:57 AM
> > > To: [EMAIL PROTECTED]
> > > Subject: Re: Early Token release
> > >
> > >
> > > Early Token Release will release the token when the last bit of the
>frame
> > > has been sent
> > > out:
> > >
> > >
> > >
> > > Faisal Athar wrote:
> > >
> > > > Hi,
> > > > Please solve my confusion for this as I am getting different answers
>from
> > > > different resources..
> > > >
> > > > Early token release
> > > >
> > > > (1) allows one token and more than one frames.
> > > > (2) Allows more than one token and more than one frames.
> > > > (3)allows more than two tokens and one data frame.
> > > >
> > > > Thanks a lot in advance...
> > > >
> > > > Faisal.
> > > >
________________________
Priscilla Oppenheimer
http://www.priscilla.com
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