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RE: [EFM] 1 Gbps != 999.9 Mbps

Roy -

I can see where your confusion comes from, if what you do is to use the marketing information on products as your basis for an understanding of what these terms mean, rather than going to the standards that define them and then trying to understand what is in the products.  Let me give you an example.

There is a product, manufactured for the SO/HO market by one of the usual names in Ethernet equipment, that my local networking supplier describes as an "8-port, 10/100 Hub". (Actually, there are a number of manufacturers that build similar devices.) Now, we know from Std 802 that a hub is a multi-port repeater designed for star-wired network cabling, so it is a shared medium (half-duplex) device. And we know from the 802.3 specs that you cannot mix 10 megs and 100 megs on the same shared medium. So what is going on here? On the face of it, this device cannot exist, as its spec claims to offer mix-and-match, auto sensing, 10 or 100 megs on each of its 8 ports.

Look further at the product spec for this device, and it says that the hub has Bridge functionality that will do address filtering between 10 megs ports and 100 megs ports. So what is really going on in this particular device is that, logically, it consists of three major components:

- An 8-port 10 megs hub (i.e., a shared medium 8-port 10 megs repeater);
- An 8-port 100 megs hub (i.e., a shared medium 8-port 100 megs repeater); and
- A 2-port Bridge connecting the two hubs together (so actually, the hubs have 9 ports, with one port on each hub permanently connected to the bridge).

So this "box" consists of three separate standardized functions, and there is no recognized, standardized name for the combination. The nearest match, from the marketing viewpoint, is to call it a hub (repeater), as the external ports are all attached to half duplex, shared medium LAN segments, and the delivered functionality is therefore understandable. However, as it also incorporates a bridging function, it is not a hub according to the way that term is defined in 802 - it is 2 hubs and a bridge that happen to have been packaged in the same box, and which happen to be able to share the same set of 8 external RJ45 connectors. From the manufacturers' point of view, it may well be easier to call it a hub than it is to go through a more standards accurate description for the benefit of the relatively small percentage of customers that would actually understand or care about the difference.

Moral: If you don't want to get confused (or confuse others) in a standards forum, or if you simply don't want to remain "just an ignorant customer" (your words, not mine!), it is a very smart move to base your terminology on the definitions contained in the standards that that forum uses/develops, rather than on the marketing information written by companies that develop products based on those standards.


At 22:38 27/09/2001 -0500, Roy Bynum wrote:


I am just an ignorant customer.  When I go to a computer store and buy a "hub", what I get is 802.1d bridge that has half duplex Ethernet ports.  I have an old "hub" that I got from a just such a store.  The box claims 802.1d bridge support.  Perhaps I am guilty of using the vernacular meanings of some terms.  But then, I am just a customer.

Thank you,
Roy Bynum

At 10:51 PM 9/27/01 -0400, Vladimir Senkov wrote:

Absolutely agree.
I didn't want to repeat myself (here and was trying to do that via personal e-mails), but i guess I just have to say that those who test they:

1) Test equipment vs. technology
2) Know what they are testing and what they are expecting as a result
Those who sell testing equipment:
1) Also sell methodologies, training and certification.
2) Some of those methodologies are in the RFCs. There are other standards for that as well.
Those who sell equipment:
1) Tell customers exactly what they are selling
2) No matter how much they want otherwise, they are going to sell the EFM, but not the "pure 1G story"
EFM needs to address specific needs of those who are going to buy it.
Those needs may include: delivering data, video, voice, whatever . . . to whatever distance, concentration of users, etc. Those needs may include: security, pricing, etc, etc.

but not just "1G". "1G" is not a need. it is more like a sign on a freeway or something . . .
let's say "upto 1G". even with OAM in-band, it will still be "upto 1G".

I'll also repeat that Ethernet performance (to the end user anyway) is NOT measured in bits per second. And nobody is selling 10Mbps repeaters/hubs (yes hub IS a repeater :) for example. They sell Ethernet hubs instead.

Therefore, customer who buys such a hub knows that he is not going to sue the seller for not delivering 10Mbps. Customer will only expect performance characteristics of that device to be tested against Ethernet performance measurement methodologies.


-----Original Message-----
From: Andrew Smith [<mailto:ah_smith@xxxxxxxxxxx>mailto:ah_smith@xxxxxxxxxxx]
Sent: Thursday, September 27, 2001 10:21 PM
To: Roy Bynum
Cc: 'stds-802-3-efm'
Subject: RE: [EFM] 1 Gbps != 999.9 Mbps


I'd be interested to see how you propose measuring one of your
802.3x-pause-rate-limited services against one of these "certification"
testers. But seriously, folks, to paraphrase that doctor-patient story
"Patient: Doctor, it hurts when I sell my customers 1000000000.0000 bps
service. Doctor: then don't sell them that, sell them what you can

Andrew Smith

-----Original Message-----
[<>]On Behalf Of Roy Bynum
Sent: Thursday, September 27, 2001 4:36 PM
To: bob.barrett@xxxxxxxxxxxxxxx; Harry Hvostov; fmenard@xxxxxxxxxxxxxxx;
'Denton Gentry'
Cc: 'stds-802-3-efm'
Subject: RE: [EFM] 1 Gbps != 999.9 Mbps


You would be surprised at how little bandwidth loss it takes for equipment
to fail certification in a services infrastructure deployment approval
process.  If we tell our customers that we are delivering a GbE, then we
deliver a GbE that will pass their most rigorous performance test,
including throughput.

Thank you,
Roy Bynum

At 12:11 AM 9/28/01 +0100, Bob Barrett wrote:

>Harry et al
>yup, all the IP 'stuff' is payload as far as the demarcation point is
>The demarc is a PHY that carries packets at the end of the day. Some
>may be buried inside a bigger system, however, the standard must also cater
>for stand alone demarc devices. My expectation as a user would be that at
>the demarc the bandwidth was the same capacity as my enterprise MAC and PHY
>of the same spec.
>Would I miss 10k per second on a 1GE, I doubt it.
>Would my test gear pick it up on an end to end private circuit test, I
>know, anyone on the reflector tried this?
> > -----Original Message-----
> > From: Harry Hvostov [<mailto:HHvostov@xxxxxxxxxxxx>mailto:HHvostov@xxxxxxxxxxxx]
> > Sent: 27 September 2001 17:41
> > To: 'fmenard@xxxxxxxxxxxxxxx'; 'Denton Gentry';
> > bob.barrett@xxxxxxxxxxxxxxx
> > Cc: 'stds-802-3-efm'
> > Subject: RE: [EFM] 1 Gbps != 999.9 Mbps
> >
> >
> > And how about the ICMP and IGMP traffic from the same CPE devices?
> >
> > Harry
> >
> > -----Original Message-----
> > From: Francois Menard [<mailto:fmenard@xxxxxxxxxxxxxxx>mailto:fmenard@xxxxxxxxxxxxxxx]
> > Sent: Thursday, September 27, 2001 6:05 AM
> > To: 'Denton Gentry'; bob.barrett@xxxxxxxxxxxxxxx
> > Cc: 'stds-802-3-efm'
> > Subject: RE: [EFM] 1 Gbps != 999.9 Mbps
> >
> >
> >
> > Or for that matter, what about ARP traffic unsolicited from my CPE
> > devices ?
> >
> > -=Francois=-
> >
> > -----Original Message-----
> > From:
> > [<>] On Behalf Of Denton
> > Gentry
> > Sent: September 26, 2001 3:12 PM
> > To: bob.barrett@xxxxxxxxxxxxxxx
> > Cc: stds-802-3-efm
> > Subject: [EFM] 1 Gbps != 999.9 Mbps
> >
> >
> >
> > > Service providers have a desire to offer a full 1GE service and not
> > > use any of it's bandwidth for OAM. The rule of conservation of
> > > bandwidth means the OAM needs to go somewhere other then in the
> > > bandwidth reserved for the 1GE payload. I take it as read that 100%
> > > utilisation of a 1GE is unlikely, but that is not the point. The point
> >
> > > is that service providers want to offer 1GE service period, not a
> > > 999.9Mbit service.
> >
> >   Does the existence of the Mac Control PAUSE frame therefore make
> > Ethernet unsuitable for service providers?
> >
> > Denton Gentry
> > Dominet Systems