WDM Gets Edgy
Continued rapid growth in packet-based services and traffic is driving the use of fiber, and ultimately WDM, deeper in metro aggregation and access networks.
Developments in both fixed and mobile broadband networks are driving the fiber and WDM trend. Here, we look briefly at both segments.
The uptake of residential fiber-based access services is increasing globally, and driving tremendous traffic through the aggregation and metro core network. We know that broadband access line growth is maturing, particularly in developed Western nations, but even as the growth rate in lines has slowed, the bandwidth delivered to subscribers continues to increase rapidly.
Speedtest.net, which has one of the most comprehensive end-user speed test databases, found the average actual download speed among Europeans running the test was 6.8 Mbit/s at the end of 2009, 9.6 Mbit/s at the end of 2010, and 13.3 Mbit/s at the end of 2011, an increase of 38% year-on-year. By December 2012, it had reached 16.7 Mbit/s, a further increase of 25%.
In the US, the average subscribed broadband speed has reached 15.6 Mbit/s, according to 2013 FCC data. At the mass market high end, CenturyLink Inc. (NYSE: CTL) offers a 40 Mbit/s DSL service, and AT&T Inc. (NYSE: T) offers 24 Mbit/s. Several cable operators in the US now sell 50 Mbit/s services.
Promising new broadband technologies such as vectoring and, in the near future, G.fast will enable speeds in excess of 100 Mbit/s and, in theory, as high as 1 Gbit/s over short copper tails.
Mobile broadband -- using high-speed mobile connections for packetized data and multimedia applications -- is driving the mobile industry today. A key point in mobile networks is that as access speeds go up, capacity in the backhaul network must also increase to cope with the new demands, otherwise the traffic bottleneck is simply moved from the radio access network to the backhaul network.
To alleviate and prevent the backhaul bottleneck, operators are rapidly migrating to fiber-based backhaul. In fact, this fiber uptake has exceeded our expectations: Heavy Reading estimates that the number of cell sites served by fiber overtook the number of sites served by microwave during 2012, and that fiber-connected cell sites will continue to grow at a faster rate than microwave during the next several years.
An operator migration to fiber (in either fixed or mobile networks) does not mandate the use of WDM, but there are some additional factors that may favor the introduction of WDM for many operators:
- First and foremost is the basic problem of fiber exhaust. Where fiber is scarce, WDM has proven far more economical than laying additional fibers. In addition, in many cases laying additional fibers in metro networks is not an option in densely built up areas with strict zoning and building restrictions.
- WDM also provides far greater spectral efficiency on the fiber compared to single-wavelength deployments, meaning more bits per second per cycle (or hertz). Spectral efficiency has become critical to operators as they seek the lowest cost-per-bit for transport equipment and squeeze the greatest possible capacity out of their existing networks (including the installed fiber plant). WDM systems today can provide up to 8 Tbit/s of capacity on a single fiber pair.
- Beyond fiber exhaust, WDM can also be used in metro Ethernet networks to create mesh and partial mesh networks that reduce reliance on the IP layer for transit traffic. Such transit traffic occupies costly router ports and is a strain on both capex (the ports themselves) and on opex (router space and power consumption). WDM is required in this application to extend metro Ethernet distances so that traffic doesn't need to terminate at intermediate nodes along the route. Another benefit of optical layer transport is reduced latency for very latency-sensitive applications, such as online gaming, financial transactions and certain cloud services.
— Sterling Perrin, Senior Analyst, Heavy Reading