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Maximizing 10GBase-T connectivity in data centers (Part 2)

Posted: 13 Apr 2012 ?? ?Print Version ?Bookmark and Share

Keywords:10GBase-T? 10Gbps? cable fiber?

In addition to the reductions afforded by advances in semiconductor technology, Base-T systems in general and 10GBase-T systems in particular are able to take advantage of some unique and standards-based algorithms exploiting the nature of computer traffic to further reduce power dissipation.

Wake-on-LAN (WoL) is a networking standard uniquely implemented on Base-T systems in which a network element, such as a server, is put to sleep until awakened by a special network signal called a magic packet. The server's network interface card (NIC) reverts to a very low power dissipation mode during the sleep period but remains alert and waiting for the magic packet. Once it arrives, the server is awakened and normal operation is resumed. Since the wakeup time associated with WoL is typically tens of seconds, it is designed for long periods in which servers are idle, such as at night or during other lengthy periods of inactivity. Even the most active of data centers experience periods when only a portion of its capacity is needed. This is a natural consequence of overbuilding resources to accommodate peak compute demands and the temporal and seasonal fluctuation in those demands due to non-uniform user locations and time schedules.

WoL can take advantage of these demand fluctuations with startling results, putting to sleep even a single typical server with a power dissipation of 500W gains much more benefit than the difference in power of hundreds of transceiver devices. It should be emphasized again that optical or direct attach links are not designed to support the WoL protocol and, therefore, force the servers and switches to which they connect to stay on and dissipate their full power around the clock. 10GBase-T, in contrast, takes advantage of WoL and benefits the data center in overall reduced power needs.

While WoL is designed for lengthy idle periods, another technology called Energy Efficient Ethernet (EEE) is specifically designed to take advantage of the bursty nature of computer traffic. Typical Ethernet traffic contains many gaps, ranging in duration from microseconds to milliseconds, that to date have been filled with so-called idle patterns in which no real computer information exchange takes place but whose waveform transitions can be used for maintaining clock synchronization between transceivers. EEE, developed by the IEEE 802.3az task force and issued as a completed standard in November 2010, defines an algorithm that exchanges those idle patterns for a Low Power Idle (LPI) mode where very little power is dissipated.

The LPI mode used during idle periods requires a new signaling scheme composed of alerts over the line, and to and from station management. During the LPI mode, a Refresh signal is used to keep receiver parameterssuch as timing lock, equalizer coefficients, and canceller coefficientscurrent. 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 3 microsecond range. The bottom line is that transceiver power savings utilizing the EEE algorithm can range between 50 percent to 90 percent, depending on actual data patterns. So to put all this information in quantitative terms, a 28nm 10GBase-T transceiver with a typical Active power dissipation of 1.5W for a 30-meter reach will dissipate only 750mW when utilizing the EEE algorithm with typical computer data patterns. System-level optimizations in switches and Ethernet controller silicon are expected to take advantage of EEE's low-power idle signaling, and save far more power than the transceiver, since they can leverage the consumption of the entire switch or server, which is more than double the power per port of even the previous generation of transceivers.

Available products
In recognition of the many advantages afforded by 10GBase-T, several networking and computer manufacturers have been introducing compliant equipment, including fixed configuration switches, blades for chassis based switches, and NICs for servers. Examples of such equipment include:

???Arista Networks 7050T 48 port fixed configuration switches
???Cisco Catalyst 4900M Switch equipped with the WS-X4908-10G-RJ45 line cards
???Cisco Catalyst 6500 Switches equipped with 16 port 10GBase-T line cards
???Cisco Nexus 2000 fabric extenders with 10GBase-T interfaces
???Extreme Networks BlackDiamond 8800-10G8Xc switches
???Hewlett Packard E5400 and E8200 switches with 10GBase-T v2 zl Modules
???Emulex OCe11102-NT
???Intel X520-T2 10GBase-T Network Interface Card
???Silicom PE210G2i9-T 10GBase-T Network Interface Card
???Dell A1667528 10GBase-T Network Interface Card

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