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markhahn0   7/4/2014 6:15:02 PM
I always find it strange how the eth world bumbles along, apparently oblivious to the IB world.  In spite of IB being almost sole-sourced by Mellanox, and that company appearing in this effort.

56Gb IB (which is admittedly 4-lane, thus 16Gb/lane) has been around for years, and is pretty much the entry level in the computational datacenter.  And it's copper.  So this whole thing is puzzling on two counts: if the demand is there, why are these eth/optical efforts lagging, and why are they insisting on optical?  power can't possibly be the issue, since we're not talking about high-density applications (even a bundle of 25 Gb coming from a rack is never going to compare to the power dissipated by the *compute* contents of the rack, or even disks.  cable *length* instead?

rick merritt
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What's after 25G serial?
rick merritt   7/4/2014 4:46:18 AM
Thanks Nicholas for cutting to the heart of the issue--the rise of the 25G serial link after so many byears of hard work.

It's easy to predict quite a big wave of products wikl ride this technology.

So what are engineers (serdes experts) turning their energies to next? I know there was a 100G serial workshop sponsored by Ethernet Allaince this month, but methinks that's pretty far future stuff, yes?

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10G,40G,100G v.s. 25G.50G,100G
Nicholas.Lee   7/4/2014 4:12:48 AM
Good article.

At first glance it might not seem obvious to readers why you would have a 40G standard and a 50G stsndard as they are so similar in speed, but this all needs to be seen through the lens of the SERDES transeiver rates on the chips.

When a 10G SERDES was the fastest transeiver available then it made perfect sense to use bundles of fibres each of which terminated at a 10G transeiver, and so we ended up with standards based on 1, 4 and 10 fibres aggregating to bandwidths of 10G, 40G and 100G respectively.

Now, chips are avilable with 25G SERDES transeivers, so companies are right to revisit the standards and update them to be based on multiples of 25G. Hence bundles of 1, 2 and 4 fibres aggregating to bandwidths of 25G, 50G and 100G Ethernet respectively.


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a practical goal
TanjB   7/3/2014 7:04:24 PM
25Gbps is where the transducers are landing for simple, single fiber capacity.  10Gbps underutilizes the hardware.  40Gbps does not look feasible without 2 or more fibers, it is an implausible step up for transducers any time soon.

In a data center with millions of connectors it makes sense to aim at the optimal feasible point which seems to be 25G for the next few years.  It is a good idea to get all the parties interested in buying and selling at this performance point to agree on compatibility.


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