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Single interconnect to improve data centre network

Posted: 16 May 2007     Print Version  Bookmark and Share

Keywords:improve Ethernet  single interconnect for data centre  Ethernet as interconnect for data centres 

A broad group of chip and systems makers is in an early stage of creating a single interconnect to link all systems in the data centre. Broadcom, Cisco, IBM, Intel and others are taking a fresh approach to improve data networking by upgrading Convergence Enhanced Ethernet (CEE). The enhanced technology can also take on jobs handled by Fibre Channel and Infiniband.

Engineers have been hammering out the concepts behind CEE for a year, although actual work on a specification is still in an early stage in an IEEE work group.

"CEE is a set of enhancements to Ethernet to allow it to better handle all the different classes of traffic in the data centre," said Renato Recio, chief engineer in IBM Corp.'s eServer networking group, and one of those leading the effort.

CEE hopes to improve the ability of Ethernet to handle complex traffic patterns in the data centre more gracefully than it does today, essentially by mapping new routing technologies onto the link layer of 10GbE. The new additions would help morph Ethernet from a "best efforts" technology that sometimes drops packets to a more sophisticated network that can slow traffic selectively to make sure no data is lost.

Attractive option
Today, data centres typically use Ethernet for networking, Fibre Channel for storage and Infiniband or a proprietary link for clusters. Supporting three nets adds complexity and cost, however. Backers say CEE could handle all three jobs. This capability would be most attractive in large data centres such as those run by Wall Street and big Websites such as Amazon and Google.

"There's a strong indication from multiple vendors that there are compelling trade-offs to go this way, and I believe this will have significant market presence," said Bob Grow, a principal architect at Intel Corp. and chairman of the overarching 802.3 group that defines Ethernet. "Whether CEE replaces all the applications people hope is the big question."

Two IBM engineers and one from Cisco Systems Inc. presented the CEE concept to the T11 group, which defines Fibre Channel, and asked T11 members to start developing by June a version of the Fibre Channel protocol that could ride on top of CEE.

"You can never tell the outcome until you see what the T11 members will do," said Robert Snively, chairman of T11 and a principal engineer in the technology and standards group at Fibre Channel switch maker Brocade Communications Systems Inc. He called CEE "an interesting concept," and not necessarily a nonstarter with the Fibre Channel community. "Everyone who is interested in Fibre Channel is also interested in making storage better," he said.

Systems makers adopting CEE will have a choice of storage protocols. Recio said iSCSI will be able to run over TCP/IP and thus over CEE. Fibre Channel, by contrast, would run directly over CEE without TCP/IP. "The performance of each option depends a lot on how it is implemented," Recio said.

Infiniband stays
Even if CEE is successful, Infiniband will still have a role, said Recio. "Infiniband will still have a bandwidth and latency advantage over CEE."

There are 10Gbps and 20Gbps versions of Infiniband available today; a 40Gbps version will ship by the end of the year. A 120Gbps version is on the road map. By contrast, only a 10Gbps version of Ethernet is shipping today.

In addition, Infiniband proponents have been trying to make inroads into storage. But efforts to improve Ethernet performance and storage capabilities with the iWarp performance enhancement and iSCSI specifications have gained only modest market traction so far.

Infiniband also aims to handle all data centre traffic, but it has been mainly limited to linking computers in high-performance clusters, thanks to its relatively high bandwidth and low latency.

CEE aims to accomplish its goals essentially through a handful of new features, starting with a congestion-management capability for Ethernet that is already being debated by the 802.1au group. Once that capability is defined, two other features will build upon it.

One is called per-priority pause. When a link becomes congested, this feature lets the system slow down only traffic that subscribes to a certain priority level, rather than slowing all traffic.

"This maps Ethernet better to environments where you have multiple layers of cascading switches," said Intel's Grow. "A credit-based system such as the one Infiniband uses is OK if there is only one layer of switches."

More enhancements
In addition, CEE backers aim to build a broad priority-processing and packet-scheduling capability upon the congestion-management feature. Finally, the group aims to develop a protocol to automatically detect when an Ethernet device has the CEE enhancements.

CEE is also expected to incorporate Internet Engineering Task Force work on something called the Transparent Interconnection of Lots of Links. TRILL is essentially an Ethernet link-layer routing protocol that provides a shortest-path frame routing in multi-hop networks.

It's not clear how much of the CEE work will be done in the 802.1au group. Some of the work may require a separate IEEE task group, Grow said.

The .1au work is fundamental, however. Once that group picks an approach to congestion management, the other pieces "will fall like dominos," Recio said.

- Rick Merritt
EE Times

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