Re: [EFM] ifSpeed & 2BASE-TL/10PASS-TS
Hugh, I knew you would take the bait. So I'd like to throw questions and example out to see what the ideas actually mean.
Some simple questions that we need to be clear on (I can guess your answers but want to ask the questions anyway):
1) Is ifSpeed covering the tx direction only? (e.g. for asymmetric links, the upstream/downstream speeds can be different)
2) Is the ifSpeed of a PME or PHY dependent on the implementation/use of various PHY overhead options? PAF header or not? FEC or not? interleaver depth?
3) What accuracy is required in the ifSpeed (e.g. its a 32bit bps counter - how accurate do we have to be)?
Do me an example:
Say we have a 10PASS-TS interface made of up 2 PMEs. One is running 2048Kbps downstream, 1024Kbps upstream, using FEC, the other is running 2048Kbps in both directions with no FEC. What would you say is the ifSpeed of the 10PASS-TS interface, and then of the individual PMEs?
> -----Original Message-----
> From: Hugh Barrass [mailto:firstname.lastname@example.org]
> Sent: Tuesday, August 03, 2004 12:48 AM
> To: Matt Squire
> Cc: STDS-802-3-EFM@listserv.ieee.org
> Subject: Re: [EFM] ifSpeed & 2BASE-TL/10PASS-TS
> I would go with 3) plus 1) - reasons:
> 0) is just plain wrong!
> 1) The aggregated links appear to the MAC and upper layers as
> a single
> link. The aggregated link speed governs the rate across the MII.
> 2) We've never accounted for "goodput" before
> 3) That's how we have done it for all other PHYs. The overhead of
> encapsulation is absorbed by the link running at a faster
> rate than the
> MII (whether it's 4b5b, 8b/10b or 64b/66b). But the effect of the IPG
> depends on the frame size, so is ignored.
> So, I think it should be the aggregate rate at the MII for an
> infinite length frame.
> Matt Squire wrote:
> >I figured I'd fire off a note to the reflectors to get this
> discussion started.
> >During the discussions today in the hubmib WG, the question
> arose as to what should be the ifSpeed for 2BASE-TL &
> 10PASS-TS interfaces.
> >Traditionally, it seems the ifSpeed has been tied to the
> speed of the MAC (e.g. 10Mbps, 100Mbps, etc.). With
> 2BASE/10PASS, the PHY may be running at a much lower speed
> than the 100Mbps MAC, so its not particularly useful to the
> administrator to call all of these interfaces 100M when the
> PHYs aren't there.
> >Options for ifSpeed of 2BASE/10PASS seem to include the following:
> >0) Use 100 Mbps (MAC speed).
> >1) Sum the physical date rates of PMEs in the aggregate (PHY speed).
> >2) Use the rate of "goodput" on the PHYs (e.g. how much data
> can ge thru). This would ignore any overhead of the PHY
> (PAF, 64/65) and overhead of the MAC (preamble, IPG). This
> most accurately reflects how much data can get thru.
> >3) Use the rate at the MAC/MII. E.g. include preamble/IPG
> (even though its not transmitted), but not PHY overhead (PAF,
> 64/65). This seems consistent with other PHYs, but is kinda
> weird in that we're not actually transmitting preamble/ipg.
> >There are probably other options too. Thoughts/opinions?
> >- Matt