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Active cables extend reach, speed of data centers

Posted: 16 Nov 2007 ?? ?Print Version ?Bookmark and Share

Keywords:active cables? data centers? interconnect reach?

As interconnect density continues to rise in high-performance computing and data centers, designers are grappling with the ensuing issues that passive cable products are inherently unable to solve.

Large bundles of copper cables with limited reach restrict airflow, increase cable weight and generally complicate cable management and routing. One way to address these problems is to use thinner cables, such as smaller wire gauge. However, the thinner the cable, the more it attenuates the signal.

"When combined with the need to support longer reaches, this creates an insurmountable problem for passive cable interconnects at high data rates. The signal simply gets attenuated and distorted too much for it to be reliably recovered by the system," said John Mitchell, senior director of marketing and application engineering, Quellan Inc.

To address signal attenuation and distortion issues in data centers, Quellan has developed a technology called Q:Active that restores signal quality by boosting the signal and reducing the noise. Q:Active components are integrated into each end of a passive cable assembly, which enhances the signal and reduces noise to provide a sharp decrease in cable gauge and an increase in cable reachup to three times that of a passive cable.

Quellan is one of a handful of companiesincluding W.L. Gore & Associates, Luxtera, Zarlink Semiconductor and Intelthat are offering high-performance data center active cable interconnects that reduce power usage, extend reach and increase speed.

Quellan's Q:Active approach for extending the reach of copper cables is threefold. First, a low-power equalizing filter compensates for the dielectric and conductor losses in the cable. Second, an integrated suite of lane management features ensures full compliance with a wide range of high-speed data transmission protocols, such as Infiniband, PCIe, 10GbE and SAS. Finally, Q:Active-enabled active cable assemblies are less sensitive to near-end crosstalk than their passive counterparts, enabling link lengths well beyond the SNR limits of a conventional passive cable.

Three products make up Quellan's portfolio: the QLx4300-S40 3.125Gbits/s quad-lane extension active copper cable; the QLx4600-S30 6.25Gbits/s quad-lane extension active copper cable; and the 6.25Gbits/s quad-lane extension active copper cable with LOS support.

These devices can be combined with Gore's advanced cabling to deliver what the companies said are dramatically lighter, thinner and farther-reaching cabling to data centers. Quellan and Gore formed an agreement in September to address the problem of large cable bundles by offering OEMs and integrators Gore Extended Reach cable assemblies, which employ the company's patented Eye-Opener+ conductor technology, with Q:Active devices. Together, this solution provides a cable with three times the reach of passive copper cables at one-third the weight and size.

Gore's Extended Reach cable assemblies employ the company's patented Eye-Opener+ conductor technology with Q:Active devices, which provides a cable with three times the reach of passive copper cables but that is one-third the weight and size.

"Gore Eye-Opener+ conductor technology in combination with Gore's low-loss dielectric material provides a signal fidelity that opens the eye and reduces cable jitter," said Kristina Mitchell, product specialist, W.L. Gore & Associates. "Quellan's Q:Active chip is then able to take this clean, but minimal, signal and regenerate it at the receive end of the cable."

According to Gore, its cables can reach distances that are 20-30 percent longer than its competitors' SPC cable or at a reduced gauge wire size requirement and still has the same reach as SPC. In addition, its Extended Reach cable assemblies use 0.25W of power per end vs. 1-2W per end for competitive cable.

Opting for optical
At Intel and Luxtera, optical active cable is the way to go. Luxtera's optical active cable connects to the same connector as copper cables and converts electrical signals to optical signals in the connector. The cable used is a fiber cable, which is thinner than copper.

Luxtera's optical active cable connects to the same connector as copper cables and converts electrical signals to optical signals in the connector.

The reach for a passive 4 x 10Gbits/s copper cable is limited to about 7m vs. Luxtera's Blazar series optical cables that can reach up to 300m. Blazar is a 40Gbit optical active cable with QSFP compliant connectors. Each lane of the four-lane, multirate cable is capable of operating at any rate from 1Gbit to 10.5Gbits for a total bandwidth of 42Gbits/s. It is the company's first product based on its patented CMOS Photonics intellectual property, implemented on a single die using a standard .13?m SOI CMOS process.

At 40Gbits/s bandwidth, Blazar provides twice the speed and three times the reach (at 300m) of existing competing optical cable products, and is packaged in a QSFP connector form factor, increasing front-panel density fourfold. Power consumption is 2.2W per 40Gbit transceiver, which is about half of comparable 10Gbit optics, according to Luxtera.

In June, Intel introduced Intel Connects Cable, an optical active cable with integrated transceivers. The cable has four 5Gbits/s lanes in each direction, for an aggregate throughput of 20Gbits/s bidirectional. These 5Gbits/s lanes support InfiniBand DDR data rates, but will also run at lower data rates to support SDR and those 10GbE CX4 installations that have power available in the CX4 socket. Intel said the cable is roughly equal in price to copper cables but extends reach to 100m.

Zarlink Semiconductor recently unveiled an optical cable interconnect that extends the reach of 10GbE data centers and high-performance computer clusters. Currently, 10GbE interconnect relies on a combination of CX4 connectors terminating copper cable assemblies for short-reach demands and pluggable optical transceivers for longer-reach requirements. The ZLynx cables are said to drive interconnect reach 10 times further than copper, while the ultrathin optical cable eliminates weight, flexibility and power concerns as data centers and computer clusters expand.

ZLynx products are one-piece fiber-optic cable assemblies with integrated, industry-standard electrical terminations capable of 20Gbits/s transmission in both directions and 5Gbits/s duplex four-channel data transmission for distances up to 100m. The ZLynx standard connector allows the optical solution to use the CX4 port. Typical power consumption is 1W per node, vs. new copper efforts in 10GBase-T that consume nearly five times more power per node, according to Zarlink.

- Ismini Scouras

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