Lighting the Way to 100G

By Verizon Communications' TJ Xia

Because of new bandwidth-intensive applications such as video on demand, interactive TV, multiple-user online gaming, high quality picture sharing, etc., the overall bandwidth demand is expected to grow over the next decade. Some experts suggest Internet traffic is expected to reach about 30 quintillion bytes per month in year 2011. A quintillion is a million-trillion, equal to a one followed by 18 zeros. That traffic amount is equivalent to moving all the information in the Library of Congress around the world in one second!

To accommodate the huge amount of Internet traffic, we have to develop a more powerful communication "pipe" to transport that information around the world. The majority of Internet traffic today is carried by optical channels at 10gbps, or 10G as it is known. But 40G technology ─ four times faster than 10G ─ is becoming more and more common in backbone networks and 100G technology will eventually arrive!

In fact, Verizon is leading the way in 100G technology development. In 2007 Verizon successfully completed the world's first 100G field trial in a commercial network, resulting in a 100G channel carrying live video traffic more than 500 km.

This year we performed the first field trial of 100G channels mixed with 10G and 40G channels on a same fiber. Why is this important? Because today’s fiber network infrastructure has established characteristics, such as channel spacing, reach distance, and fiber types, carrying both 10G and 40G channels. The challenge is that the newly developed 100G channel must fit into the existing infrastructure, not affect the 10G and 40G channels and maintain its integrity.

In other words, the goal of this trial was to demonstrate that 100G technology is practical in real field fiber. The result? We successfully transmitted the 100G channel with multiple 10G and 40G channels over 1,040-km of field fiber with off-line processing.

One of the keys to this trial was the use of the CP-QPSK modulation format. The modulation format determines how the signal is carried – whether it’s in the amplitude, in the phase, or in the polarization. CP-QPSK modulation stands for the tongue-twisting format called “coherently demodulated polarization multiplexed quadrature phase shift keying.” The advantage of this modulation format is that the 100G channels fit into the tiny 50-GHz channel spacing – the traditional channel spacing for 10G and 40G channels. Maintaining the traditional channel spacing is important because it means the 100G signal can be carried over the existing network without investing in new fiber infrastructure.

The other significant outcome of this trial is related to the high tolerance of the 100G signal to the infamous fiber impairment called PMD, or polarization mode dispersion. The PMD effect is a phenomenon that splits the signal into two parts that travel at slightly different speeds. The result is the signal is deformed when it arrives at the receiver end. If a signal has high PMD tolerance, it’s resilient to the impairment and can maintain signal integrity. Fortunately, 100G technology has strong digital signal processing power so the deformation of the signal can be easily corrected at the digital level.

Not only can PMD affect the signal, but it can also be impacted by the launch power of the neighboring channels, which affects the signal quality. In this trial, the results showed the 100G channel is error free with forward error correction (a form of signal error correction) as long as the launching powers of the neighboring 10G and 40G channels are below certain levels. The bottom line is this trial verified that a 100G channel is able to work with neighboring 10G and 40G channels in an existing fiber network while maintaining the level of quality our customers expect.

Consumers who are channel surfing through the variety of channels available on Verizon FIOS and commercial customers who are sending large data files over Verizon’s global network can all rest easy knowing Verizon engineers are working hard in the lab and in the field to deliver the quality, reliability and functionality for which Verizon is known.

Share this article: Email, Slashdot, Digg, Del.icio.us, Yahoo!MyWeb, Windows Live Favorites, Furl
Add this article feed to: RSS, My Yahoo, Newsgator, Bloglines