100-Gbps Ethernet is coming
Martin Rowe, Senior Technical Editor m.rowe@tmworld.com -- Test & Measurement World, 12/1/2007
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On December 5, the IEEE formally established IEEE 802.3ba as the designation for a 100-Gbps and 40-Gbps Ethernet communications standard. Higher-speed Ethernet is being driven by our insatiable appetite for bandwidth. Much of the demand comes from on-demand IPTV, peer-to-peer video, and video-sharing Web sites such as YouTube.
A 100-Gbps Ethernet (100 GbE) link will require multiple transport lanes, but the channel architecture is currently undefined. The standard will likely specify either 4x25-Gbps lanes or 10x10-Gbps lanes (see figure), because transmitting a single lane at 100 Gbps isn’t possible with today’s technology. Specifications for both optical and electrical physical layers are likely to be developed.
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| 100 GbE links will likely use either four or ten data lanes. |
Service providers will likely go for 100-Gbps Ethernet links for their core networks. Data-center operators are leaning toward 40 Gbps (Ref. 1). “The people who connect servers, switches, and routers see a need for moving from 10 Gbps to 40 Gbps,” said Larry Green, chief technologist at Ixia, “but they won’t want 100 GbE right away because the optics are too expensive.”
“Ethernet is expected to map over 40-Gbps OC-768 SONET networks,” added Greg LeCheminant, senior product marketing engineer at Agilent Technologies. “The IEEE high-speed study group will pursue both 100-Gbps and 40-Gbps specifications in the standard.”
Ken van Ormen, product manager at Spirent Communications, commented on transmission distances. “The goal is to get 40 km,” he said. Service providers will use the intended 10-km and 40-km links on single-mode fiber. Data centers will look at 100-m links with multimode fiber and 10-m links over copper wire or backplanes.
For several channel architectures and lengths, signal receivers will have to equalize incoming signals to compensate for transmission distortion. “You can’t look at the eye diagram of the transmitter to know what a receiver will see,” noted LeCheminant. “You have to know the channel and how the receiver must equalize the waveform.”
He expects that the transmitter waveform dispersion penalty (TWDP) test, specified in IEEE 802.3aq, may again be an important test (Ref. 2). This test requires you to capture a waveform at the transmitter and digitally process it through a simulated channel. From the results, you can calculate the distortion, or “penalty,” in the channel and design an equalizer for the receiver (Ref. 3).
The 100-GbE and 40-GbE specifications will likely be ready by the end of 2010. Interoperability testing will follow.
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| Presentations from the November 2007 meeting of the High Speed Study Group are available at grouper.ieee.org/groups/802/3/hssg/public/nov07. |
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