RE: Point-to-Point Links
Hi,
An alternative to the flow control approach may be the pre-determined rate
approach (like in ATM). The rate of any flow is predetermined. The MAC can
do the work of rate adaptation, as it does anyway in the case of WAN PHY
Interface. The mechanism has to be more general, to support: 1. A
programmable Rate. 2.Do it also for LAN PHY.
Boaz
> -----Original Message-----
> From: Rich Taborek [mailto:rtaborek@xxxxxxxxxxxxx]
> Sent: Sunday, December 24, 2000 8:41 AM
> Cc: 802.3ae
> Subject: Point-to-Point Links
>
>
>
> Ben, Brad,
>
> We're about 5 or 6 tangents off the old main thread by now,
> so I started
> a new one. I'd like to take this opportunity to clear
> something up about
> 802.3 point-to-point links, including those being specified in IEEE
> P802.3ae. At least I'd like to see some discussion on this topic :-)
> Section, Line and Path are not relevant for any P802.3ae
> links, whether
> they be LAN or WAN links. There is quite a bit of "bleeding" of
> management information for SONET Section, Line and Path into
> the WIS. I
> assume that the reasoning for this is to support the
> management of this
> SONET/SDH specific information in a "standard" manner.
>
> What I don't see in the current draft is any description of or any
> requirement for the distinction of Section, Line, or Path. The link
> between two P802.3ae PMDs, whether they be two LAN or WAN
> PMDs is simply
> a point-to-point link. Section, Line and Path are only relevant in
> SONET/SDH equipment to which a WAN PHY may be attached. In
> the case that
> the SONET/SDH equipment and its associated Sections and Lines
> and Paths
> bisect two WAN PHYs, we have two point-to-point links and a SONET/SDH
> cloud in between. I don't believe that 802.3x flow was
> designed for the
> latter configuration.
>
> I agree with Brad's wording: "Flow control is also only for
> point-to-point links". I don't believe that either 802.3 flow
> control or
> point-to-point links are applicable to or representative of
> "WAN links".
> Note that "WAN link" is usually typically synonymous with
> SONET/SDH WAN
> links rather than IEEE 802.2 WAN links, whether based on LAN
> or WAN PHY
> links.
>
> We certainly have a terminology problem. WAN flow control is an issue
> which is beyond the scope of 802.3 and simple 802.3x
> point-to-point flow
> control.
>
> Happy Holidays,
> Rich
>
> --
>
> Ben Brown wrote:
> >
> > Brad,
> >
> > I just wanted to pick up on something you wrote:
> >
> > "Booth, Bradley" wrote:
> > >
> > > Flow control is also only for point-to-point links.
> > >
> >
> > I hope you aren't implying that a WAN link with multiple
> > lines & sections (do I have the nomenclature correct?) is
> > not a point-to-point link. From an ethernet MAC perspective,
> > these are just as point-to-point as a 3 meter jumper.
> >
> > I can't even begin to imagine the amount of buffering
> > required to run .3x flow control over such a link. I would
> > be interested in a short note from someone with experience
> > regarding what kind of potential latencies such a link
> > might have.
> >
> > Thanks,
> > Ben
> >
> > "Booth, Bradley" wrote:
> > >
> > > Time to hit the RESET button on this one. :-)
> > >
> > > First, you are correct in the assumption that a 40km link
> buffer requirement
> > > (1MB, not Mbit) will greatly exceed the internal latency.
> > >
> > > Not everyone in the world will design equipment to work
> up to 40km. Some
> > > will create equipment that works up to 65m, and to
> optimize that equipment,
> > > they're not going to want to have 1MB of buffering just
> for flow control
> > > (that would be overkill). In these short distance
> applications, knowing the
> > > maximum latency in the link partner device and in the
> local device will
> > > permit designers to optimize their flow control buffering.
> > >
> > > Flow control is also only for point-to-point links.
> > >
> > > Happy holidays,
> > > Brad
> > >
> > > -----Original Message-----
> > > From: Roy Bynum [mailto:rabynum@xxxxxxxxxxxxxx]
> > > Sent: Friday, December 22, 2000 10:31 AM
> > > To: Manish D. Agrawal; Boaz Shahar;
> Manish D. Agrawal;
> > > THALER,PAT (A-Roseville,ex1); HSSG
> > > Subject: RE: delay constraints
> from XGMII to XAUI
> > >
> > > Manish,
> > >
> > > One of the issue of the delay is that
> there are other
> > > distances
> > > involved. The 850nm 65m PHY will not
> have the same
> > > transmission media
> > > latency as the 1500nm 40km PHY. Add
> latency due to long
> > > haul optical
> > > services for the WAN PHY and you have got
> even more issues
> > > with flow
> > > control response latency. These are
> going to be issues of
> > > discussion as we
> > > go forward.
> > >
> > > Thank you,
> > > Roy Bynum
> > >
> > > At 11:32 AM 12/22/00 +0530, Manish D.
> Agrawal wrote:
> > > >Hello Boaz,
> > > >
> > > >As you said "The only MAC requirement I
> can think of for
> > > bounding the
> > > >lower layer delay is for buffer sizing
> for 802.3x flow
> > > control. That has
> > > >been the factor for keeping the delay
> tables in various
> > > clauses. "
> > > >
> > > >But, since the delay for the flow
> control seems to be
> > > greater than 1 Mbit,
> > > >why there are delay constraints of
> 256/212/272 bits in
> > > various clauses,
> > > >which are negligible as compared to the
> delay of 40KM
> > > fiber?
> > > >
> > > >Correct me if I am wrong.
> > > >
> > > >Best Regards,
> > > >Manish
> >
> > -----------------------------------------
> > Benjamin Brown
> > AMCC
> > 2 Commerce Park West
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> > -----------------------------------------
>
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