Debunking 10GBase-T Myths

The LPI mode used during idle periods requires a new signaling scheme composed of alerts over the line and alerts to and from station management. When in the LPI mode, a refresh signal is used to keep receiver parameters, such as timing lock, equalizer coefficients, and canceller coefficients, current. These are also critical to enable fast transitions from LPI to active modes. Typical transition times from active to LPI mode and back are in the three-microsecond range, so implementation of EEE introduces minimal latency into the network. The bottom line is that transceiver power savings using the EEE algorithm can range from 50 percent to 90 percent depending on actual data patterns. For example, a 28-nm 10GBase-T transceiver with a typical active mode power dissipation of 1.5W for 30-meter reach will dissipate only 750W when using the EEE algorithm with typical computer data patterns. Even better, system-level EEE optimizations implemented in switches and Ethernet controller silicon are expected to save far more power than EEE optimizations in the transceiver because the energy consumption of the entire switch or server (which is more than double the power per port of even the previous generation of transceivers) can be leveraged.

10GBase-T “short reach” mode is another power-dissipation strategy

Another feature present in 10GBase-T PHYs, which can greatly aid in the reduction of overall power dissipation, is the ability to automatically detect channel length between compliant transceivers. When the channel length is less than 100 meters, 10GBase-T transceivers are able to reduce their power dissipation while still maintaining fully compliant bit error rate (BER) performance. This so-called “short-reach” mode takes advantage of the larger signal-to-noise ratios (SNR) present due to lower signal attenuation in short channels, and the power-dissipation reductions can be dramatic. For example, because the signal strength at the transceiver is significantly larger if it is attenuated by only 10 meters of cabling as opposed to 100 meters of cabling, transmit power can be significantly reduced without adversely affecting BER. It is a common misperception that short-reach mode is an on/off condition that is directly tied to a specific link length (e.g. 30 meters). In fact, the short-reach mode power-dissipation profile is contiguous and scalable versus length.

In short-reach mode, not only can transmit power be reduced, but the number of filter taps used for echo cancellation and line equalization also can be curtailed and powered down internally in the device. As an example, a transceiver typically with 3.5W of power dissipation when connected to a 100-meter channel can exhibit power dissipation of only 2.5W when connected to a 30-meter channel, or less than 2W when connected to a 10-meter channel. Because many newer data center configurations rely on shorter cable lengths than the maximum length of 100 meters, exploiting this feature is growing in importance.

The most cost-effective 10-Gbit/sec Ethernet applications

While reach, power consumption and backward compatibility are important considerations when selecting media, most designers will assert that cost significantly influences the decision-making process. The truth is that 10GBase-T offers more benefits and flexibility than other 10-Gbit/sec applications at the most favorable price point. Figure 3 shows the equipment (server port and NIC), media and annual maintenance costs for one channel and its corresponding 10-Gbit/sec port connections, which are representative of the types and lengths of media commonly deployed in data centers.

Figure 3:  Per Port Cost Comparison: 10Gb/s Ethernet versus Media Types

The most economical choice for 10-Gbit/sec transmissions is 10GBase-T network equipment in conjunction with Category 6A UTP, Category 6A F/UTP, or Category 7A S/FTP balanced copper twisted-pair cabling. The same conclusion is reached when this analysis is repeated for channels and their corresponding port connections that represent the types and lengths of media commonly deployed in horizontal LAN cabling. It is this cost advantage that will drive the rapid adoption of 10GBase-T in 2012.

Interest in speeds beyond 10 Gbits/sec over copper balanced twisted-pair is growing

The most significant confirmation that Base-T Ethernet applications have a strong future is the growing interest in “next-generation” cabling. This media will be targeted to support the copper balanced twisted-pair application that comes after 10GBase-T. Because Ethernet applications in the LAN backbone and data center core have always preceded Ethernet specifications for the LAN horizontal and data center edge, it is a good bet that the next Ethernet over balanced twisted-pair speed will be 40 Gbits/sec to supplement IEEE 802.3ba-compliant 40-Gbit/sec Ethernet computer backplanes and optical-fiber network gear. At this time, the biggest driver demonstrating the great industry commitment to, interest in and investment in the future of copper-based Ethernet is the work being done by the ISO/IEC and TIA to develop next-generation cabling specifications to support such an application.

ISO/IEC recently initiated a project to develop a new standard tentatively titled “ISO/IEC 11801-99-x Guidance for balanced cabling in support of at least 40 GBit/s data transmission.” This proposed two-part standard will address capabilities of both existing ISO/IEC 11801-compliant channels and channels with extended and/or enhanced performance characteristics. TIA is currently working on a project called “Specifications for 100Ω Next Generation Cabling,” expected to be published as Addendum 1 to ANSI/TIA-568-C.2. These massive project initiatives reaffirm the strength and popularity of Base-T applications and balanced copper twisted-pair cabling media.

While 10-Gbit/sec Ethernet-ready copper balanced twisted-pair cabling has been available for some time, it has been a long and anxious wait for 10GBase-T equipment to reach the broad market. That wait is over. 10GBase-T network equipment offers greater reach and flexibility than any other 10-Gbit/sec copper solution and is a very attractive alternative to 10-Gbit/sec optical fiber solutions when deployed channel lengths are less than 100 meters. Data center and LAN IT managers who had the foresight to install 10-Gbit/sec Ethernet-ready copper balanced twisted-pair cabling in their network are poised to capitalize on the negotiation and power-reduction features of 10GBase-T and begin incremental server and switch upgrades to relieve network congestion and increase capacity this year. The rest have a little catching up to do.

About the Authors

Ron Cates is vice president of marketing, networking products, at PLX Technology, a leader in 10GBASE-T transceivers.  Prior to PLX, he was senior vice president and general manager of Wide Area Networking Products at Mindspeed Technologies. He has over 30 years of experience in the semiconductor industry and holds BSEE and MSEE degrees from the University of California at Los Angeles and an MBA from San Diego State University.  He can be reached at rcates@plxtech.com.

Valerie Maguire, BSEE, holds the position of global sales engineer at Siemon, a world-class manufacturer of high performance copper and optical fiber cabling systems.  She holds various leadership positions with the TIA TR-42 Telecommunications Cabling Systems Engineering Committee and IEEE 802.3 Ethernet Working Group.  In addition, She has authored over 45 technical articles and engineering papers, holds one U.S. patent, and received the 2008 Harry J. Pfister Award for Excellence in Telecommunications.  She can be reached at valerie_maguire@siemon.com.

References:

[1] IEEE 802.3at™, “IEEE Standard for Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications Amendment 1: Physical Layer and Management Parameters for 10 Gb/s Operation, Type 10GBASE-T”, September 2006

2 The Linley Group, “A Guide Ethernet Switch and PHY Chips”, December 2011

3 IEEE 802.3az™, “IEEE Standard for Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications Amendment 5: Media Access Control Parameters, Physical Layers, and Management Parameters for Energy Efficient Ethernet”, October 2010

4 IEEE 802.3ba™, “IEEE Standard for Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications Amendment 4: Media Access Control Parameters, Physical Layers, and Management Parameters for 40 Gb/s and 100 Gb/s Operation”, June 2010