Electronic Design

System Extends InfiniBand Cable Reach To 100 m

Intel's Connects Cables will have many designers wondering why they didn't come up with the idea themselves. These cables address the InfiniBand market, where this technology and its high data rate are widely used to interconnect multiple servers in clusters and in supercomputer installations.

InfiniBand uses a four-channel copper cable 10 m in length with special connectors to achieve data rates up to 20 Gbits/s. These large, heavy, and very expensive cables put a real burden on data-center overhead and restrict expansion efforts. Alternative schemes, like 10-Gbit Ethernet over twisted-pair copper systems, have been developed to help. But the Connects Cables may have won the battle.

The Connects Cables use fiber. Fully electrically compatible with standard InfiniBand 4x and Ethernet 10GBaseCX4, they feature electrical-to-optical and optical-to-electrical transceivers (see the figure). With four independent paths capable of 5 Gbits/s each per cable, the maximum data rate hits 20 Gbits/s, which can be achieved easily in a 100-m cable. This length mitigates expansion problems and provides other benefits as well.

Compared to an equivalent length of standard 24 AWG copper cables, the Connects Cables are thinner and 84% lighter with 83% less volume. Less volume means better circulation, allowing greater airflow in the system—something every data center needs. And, the bend radius is 40% smaller.

The Connects Cables produce minimum electromagnetic interference and pose no risk of ground loops. They deliver a low bit error rate (BER) of 10–15. Optical/electrical conversion time is only 275 ps at each end of the cable for a maximum latency of 550 ps.

Tektronix helped Intel meet the requirements of the InfiniBand Trade Alliance Compliance Working Group in developing this cable. InfiniBand cable test specifications require signals with a specific impairment to be provided from a signal source. Intel accomplished this using a Tektronix AWG arbitrary waveform generator transmitting a test pattern at 5 Gbits/s.

Also, Intel used the Tektronix Direct Synthesis method to create the signal impairment. Intel then used eye diagrams to evaluate transmission integrity. Next, Intel used the Tektronix DSA8200 Digital Signal Analyzer to measure jitter and eye. Advanced jitter, noise, and BER analysis software analyzed the cable's BER down to its 10–15 BER specifications.

Tektronix has been testing InfiniBand cables since 2002, when the first SFF8470 cables were approved. Every SFF8470 cable that is certified in the industry today has received that certification using a Tektronix TDS/CSA/DSA 8200-based system.

Intel's new cables will be used as part of the backbone network at next June's International Supercomputing Conference in Dresden, Germany. They will make the creation of high-performance computing clusters more practical, permitting them to become more mainstream as they tackle a variety of challenges in medical research, weather forecasting, computer-aided design, and financial modeling.

Intel Corp.
www.intel.com
Tektronix Inc.
www.tektronix.com

TAGS: Intel
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