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TEST & MEASUREMENT WORLD: 100-Gbps Ethernet is coming

In December 2007, the IEEE formally established IEEE 802.3ba, the designation for a 100-Gbps and 40-Gbps Ethernet communications standard. The 100- and 40-GbE (Gbps Ethernet) specifications will likely be ready by the end of 2010. Interoperability testing will follow. A 100-GbE link will require multiple transport lanes, but the channel architecture is currently undefined. The standard will likely specify either 4
25-Gbps lanes or 10
10-Gbps lanes because transmitting a single lane at 100 Gbps isn’t possible with today’s technology. Expect to see specifications for both optical and electrical physical layers.

Service providers will likely go for 100-Gbps links for their core networks. Data-center operators are leaning toward 40 Gbps. “The people who connect servers, switches, and routers see a need for moving from 10 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 40- and 100-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- and 40-km links on single-mode fiber. Data centers will look at 100m links with multimode fiber and 10m 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 TWDP (transmitter- waveform-dispersion-penalty) test, specified in IEEE 802.3aq, may again be an important test. 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.