Electronic Design

Short-Reach 10GBaseT Cuts Power Consumption In The Data Center

As IT managers deploy new applications in the data center, bandwidth demand is outstripping capacity. Applications such as video streaming and the relentless demand for storage are pushing IT networking infrastructures beyond their limits. At the same time, IT managers are under pressure to reduce power consumption in the data center as well as the total cost of ownership (TCO).

Fortunately, the next evolution of Ethernet is approaching deployment readiness. The Dell'Oro Group, a market research company based in Redwood City, Calif., projects 10-Gbit Ethernet (10GbE) over copper will grow to 42% of an 8.8M unit (total 10GbE) by 2010.

Transporting 10GbE over twisted-pair copper is by no means a trivial feat, especially when attempting to provide adequate signal integrity at the traditional 100-m cable reach. Moreover, using currently available process technologies, long-reach transceivers typically consume more than 10 W.

This will significantly impede the adoption of 100-m 10GbE transceivers since power consumption above 5 W severely limits practical deployment of 10GBaseT solutions in the data center. What is needed is a tradeoff between power consumption and cable reach.

Making the tradeoff
According to IEEE estimates, greater than 80% of data-center cable runs are less than 30 m. For this reason, the recently ratified IEEE 802.3an (10GBaseT) standard offers a low-power mode (30-m reach), which provides the ability to trade reach for power. This tradeoff significantly reduces heat density, power costs, and the capital expenditures required to dissipate the additional heat.

When viewed from either the system interface or the front panel RJ-45 connector, it is impossible to identify any differences electrically, mechanically, or in any other way between a 30-m transceiver and a 100-m transceiver. The only difference is the length of cable supported and a bit in a management register that indicates short-reach operation.

IEEE 802.3an clearly defines and completely specifies all aspects of short-reach operation. It also provides a means to verify interoperability and compliance to the short-reach requirements of 10GBaseT by specifying test channels for both Category 6a (Cat6a) and Category 7 (Cat7) cabling. A transceiver that meets all of these requirements is in compliance with the short-reach provisions of IEEE 802.3an.

Signal integrity is another factor that poses a unique challenge for 10GBaseT transceivers. It's hard to ignore the fact that at 10 Gbits/s over 100-m copper cable lengths, we have exceeded the theoretical and practical signal-integrity limits (i.e., Shannon's limit) of Category 5e (Cat5e) cabling. This fact precipitated the development of a new cable type-Cat6a. Add to this the need to provide sufficient headroom (usually 20% to 30% additional cable length) to satisfy the OEM's rigid requirements, and the technological challenges loom larger than ever for 100-m 10GBaseT solutions.

Bigger isn't better
As one would expect in any semiconductor solution, size matters. The footprint of a solution dictates cost, port density, power consumption, heat dissipation, board space, and packaging. Low-power, short-reach 10GbE transceivers will consume less than 5 W in a very small (singlechip) footprint, qualifying them for rapid adoption and deployment either as fixed-port (chip-on-board) solutions or in MSAcompatible modules (e.g., X2, XFP and SFP+).

Besides providing robust signal integrity and consuming half the power of present-day long-reach alternatives, deploying short-reach transceivers in these modular solutions will also provide OEMs the flexibility to offer a backward-compatible, legacy-friendly 10GbE-over-copper upgrade path. It also accelerates time-to-market for the physical-layer (PHY) vendor by creating an intermediate step toward the PHY's ultimate chip-onboard deployment in OEM systems.

As power density in the data center continues its inexorable climb to the top of the IT manager's list of hot buttons, the value of the short-reach 10GBaseT solution may well become the pivotal factor in the successful deployment and commercial viability of 10GbE over copper.

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