A short history of 100G DWDM optical network transport development

As long-haul dense wave division multiplexing (DWDM) growth is accelerating, interest in 100G DWDM optical network transport continues to surge, even as operators deploy 40G DWDM systems to increase optical channel rates. To discover the reason for the rush, review the history of increasing optical channel rates and the challenges facing trials and deployment and production networks.

Editor's Note: In part two of our expert lesson on 100G DWDM optical network transport, Eve Griliches, managing...

partner of ACG Research, provides a short history of 100G DWDM optical network transport and an assessment of 100G DWDM trials.

Don't miss the rest of this expert lesson on 100G DWDM optical network transport:

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A short history of 100G DWDM optical network transport development

It comes as no surprise that traffic growth is the underlying driver for 100 Gigabit (Gbit) Dense Wave Division Multiplexing (DWDM) network transport. This was the case with the transition from 2.5G to 10G and from 10G to 40G and now 100G optical channel rates.

As the number of Internet users expands, bandwidth per user is increasing, putting enormous pressure on metro networks and core backbone networks.

Eve Griliches
Managing Partner
ACG Research

Telecom carriers and independent vendor assessment reports estimate 50% to 60% traffic growth year over year. As the number of Internet users expands, bandwidth per user is increasing, putting enormous pressure on metro networks and core backbone networks.

Routers with 10G and 40G interfaces emerged to hand off to DWDM transmission equipment, driving the need for 40G wavelengths. Router handoffs will ultimately push the need for 100G as access streams into routers become higher data rates (10G and higher) that force the transport backbone link to go to an even higher rate.

Changes in network architecture are another driver for higher-bit-rate networks. In the past, providers had separate networks for each access technology or service. Today, most providers are attempting to put these services and technologies onto one IP backbone, which puts pressure on the core backbone to handle much more traffic. When AT&T merged multiple networks (SBC and BellSouth), for example, it led to integrated networks overflowing onto one large backbone that required an immediate upgrade to 40G and is now 100G capable.

Consolidating traffic onto fewer wavelengths and the associated economics were other factors for the transition. Larger bandwidth wavelengths have always promised better operation efficiencies merely because there are fewer wavelengths to manage and a smaller number of parts in the network that can fail.

In the drive toward faster optical channel rates, some major providers have already moved to 40G networks:

  • Comcast has one of the largest IP-over-WDM 40G deployments for its national network, deployed with Cisco CRS-1 integrated optics and Nortel transmission equipment.
  • In Japan, NTT is offering a 40G network service over a wide-area Ethernet network.
  • Verizon has deployed live traffic on 40G links on high-bandwidth routes with Alcatel-Lucent equipment.
  • Deutsche Telekom (DT) also has deployed a 40G network on equipment from Ericsson (Marconi).
  • Sprint Nextel started upgrading its 10G network to 40G using Cisco's IP over WDM and Ciena's CoreStream.
  • In October 2008, AT&T completed its IP/MPLS backbone network with more than 80,000 fiber optic wavelength miles of 40G running on Nokia Siemens' ULH platform. According to AT&T, every 10G lambda will be a 100G lambda by 2012 because of 60% traffic growth year over year.

100G DWDM network transport performance trials and tribulations

For the last two years, various 100G DWDM network transport technology experiments have come to market, all with different distances, alternative formats and widely disparate margin allocations. It is technically feasible to light one wavelength on great fiber and go a few hundred kilometers. It is a totally different proposition, however, to have preproduction equipment running thousands of kilometers with multiple 100G DWDM wavelengths while assuming system operating loss margins.

Vendors must take into account optical signal-to-noise ratio (OSNR) after transmission (the loss incurred), nonlinear transmission penalty, polarization mode dispersion (PMD) and filtering (ROADM) penalty, as well as aging and end-of-life margins. Real-world performances in the field versus hero experiments take into account these penalties before announcing performance metrics.

Some companies are conducting performance metrics. Comcast executed a realistic trial on the same fiber as 10G and 40G wavelengths for 100G with dual-polarization quadrature phase-shift keying (DP-QPSK) on a 300 km span with live traffic. Verizon has tested 100G with Nokia Siemens Networks (NSN) over a 1,000 km in the lab and has also tested Nortel 100G on very high PMD fiber with 10G and 40G wavelengths running on the same fiber. AT&T has also tested NEC over 600 km. The outcome was that these products, which were prototype hardware, met challenging yet forgiving situations.

Read more on 100G DWDM optical network transport development, including articles on how the telecom industry is preparing for 100G DWDM optical network transport development and enabling technologies for 100G DWDM network transmission.

About the author: Eve Griliches, managing partner of ACG Research, has extensive experience in technology product management and the telecommunications industry. She was IDC program director for the Telecommunications Equipment group, where she provided in-depth analysis on many key technologies in the telecom market. Her product management experience at network equipment vendors include Marconi (Ericsson), PhotonEx, Nortel Networks, Bay Networks and Welfleet. She can be reached at [email protected].

This was last published in April 2010

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