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IEEE group to decide on 25G Ethernet standard

Posted: 22 Jul 2014 ?? ?Print Version ?Bookmark and Share

Keywords:25G? Ethernet? IEEE?

An IEEE 802.3 group made a vote to set standard for the 25Gbit/s Ethernet that will be used in data centres in the wake of its launch in June.

At a July 15 meeting, 121 of 148 engineers voted to start a group to work on the interface that will link rack-mounted servers to top-of-rack switches in large data centres. Fifty-nine people at the meeting said they would join the group. Representatives of 39 companies expressed interest.

In a straw poll at a March IEEE meeting, just 30 engineers voted to start a 25G standards effort, with 27 voting against and 21 abstaining. At that time, representatives of 25 companies expressed support for such an effort.


25GE targets the server to leaf switch link. (Source: IEEE 802.3)

A panel kicked off the meeting making the case for 25G as the next step from today's 1G and 10G links, leveraging an emerging class of 25G SerDes. They included representatives from Broadcom, Cisco, Dell, Intel, and Microsoft.

In addition to the panelists, those voting for the new effort included engineers from Applied Micro, Avago, Fujitsu, Hewlett-Packard, IBM, Juniper, Marvell, and ZTE.

25G could slash the number of top-of-rack switches

Backers say 25G could slash the number of top-of-rack switches large data centres need. (Source: IEEE 802.3)

Compared to the participants in the March discussion, last week's panellists provided a much more detailed description of the use case and economic arguments for a 25GE standard, according to Rochan Sankar, a product marketing director from Broadcom's networking group.

Consortium already driving a spec

The concept of a single 25GE lane leverages 4G x 25G IEEE specifications for 100G Ethernet, as well as 25G work at the Optical Internetworking Forum.

The 25G Ethernet Consortium formed in June already has a spec available to its members. Brocade and Dell recently joined founders Arista, Broadcom, Google, Mellanox, and Microsoft.

10G will dominate by 2018

Market watchers say 10G is just getting started in servers but will dominate by 2018. (Source: Crehan Research)

The consortium is focused on getting more companies to agree to its spec, parts of which might still be modified. "There may be some minor details to iron out," Sankar said. Nevertheless, he expressed optimism that a single standard will emerge from the efforts of the new IEEE group and the consortium.

The consortium is also promoting a 50G spec using two 25G SerDes lanes. The IEEE group could decide whether to embrace that concept when it meets in September.

The consortium's 25G spec is targeted at copper as the lowest-cost medium for use in the server rack, Sankar said. Some members such as Mellanox talked about the use of silicon photonics when the consortium was announced last month.

25GE is already specified for a number of standards

25GE is already specified for a number of standards, including 100GE. (Source: IEEE 802.3)

Broadcom seems silicon photonics as more appropriate for use deeper into the data centre over distances of more than 30m between the top of the rack and aggregation switches also called leaves and spines. For the 3m or so within a server rack, "25G per lane on copper is just fine, you have plenty of margin to work with, and it's the lowest-cost option."

- Rick Merritt
??EE Times

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