Legacy support and low cost are the two vital factors in planning metro optical upgrades, said Kathy Tse of AT&T's Optical Transport Planning at the OFC Service Provider Summit in Atlanta this week. CWDM is of great interest to AT&T due to its low cost, standards-defined integrated optics for interconnection, and its ability to leverage existing and fiber. AT&T is also seeking ways to reduce capital expenditures through the elimination of unneeded OEO connections and the use of lower cost components. Operating expenses will be reduced through automation of system maintenance and growth and reduced power and footprint. However, Tse said it is rare to find a business case for new CapEx outlays that really achieve significant OpEx savings.
Planning for metro optical networks requires careful consideration of the access network, advised Dr. Andreas Gladisch of Deutsche Telekom, T-Systems. He feels that it no longer makes sense to deploy the traditional SONET/SDH systems. The time is right for next generation SONET/SDH equipment capable of carrying a mix of services. He argues this is a better option than combining pure SONET/SDH and pure Ethernet as point solutions.
France Telecom R&D's Francois Tillerot believes that the diversity of customer applications means there is no single optimal solution for metro optical networks. In reality, most carrier networks are built with different topologies or equipment in each city. This is particularly true for large service providers that have grown through mergers and acquisitions over the years. Tillerot believes that CWDM is economical for specific circumstances and customers, but it is not a global solution. To integrate and deliver Ethernet services, Ethernet over SONET/SDH and to some degree CWDM will be most effective, while DWDM remains very expensive and probably most useful online in areas where fiber is scarce.
It is still better for an enterprise to operate a separate data network rather than create or utilize converged network, according to R. Brad Kummer, CTO of Cogent Communications. Traditionally, bandwidth has been considered an expensive resource that must be carefully managed with an elaborate network made up of expensive multi-services equipment and management systems. Cogent's view is that bandwidth can be inexpensive when carried on a simply designed network, and that the liberal application of bandwidth can solve networking problems. Cogent offers data-only service over its network, which is essentially a nationwide Layer 3 switched LAN. Cogent is not positioning its network for voice or other time sensitive services, making its 1-3 second fail over time acceptable. Internet data applications are designed to deal with this, says Kummer. Cogent utilizes WDM systems in its long haul network to minimize its transport costs, and in its metro network to minimize network costs. Cogent has recently switched from DWDM systems to more cost effective CWDM.
Mark Jones of Sprint's Optical Transport and Networking Group agrees that it is easier and generally more cost-effective to add bandwidth to a simple network architecture than manage a complicated network full of differentiated services. He believes that there have been several years of hype about technologies that are unrealistic when one evaluates the equipment available and the actual network costs. His list of top fallacies created by market hype includes full transparency, wavelength-level bandwidth on demand ("a hopeless business case"), and the belief that new technology is inherently better than old. Ultimately, optical networking decisions should be driven by an evaluation of the total network cost. No one optical networking solution will be right for all situations, and those who are "technology agnostic" will have the upper hand when considering their choices.
A pure packet architecture is the endgame, said Sabrina Calhoun, Director of Operations Engineering for Cox Communications. Cox has three parts to its network: an IP backbone; a transport network made up of Cox's own fiber to connect headends out to each neighborhood; and a coaxial network to connect directly to homes. Cox embarked on the upgrade of its network several years ago in order to offer telephony. For better network reliability, Cox moved to a self-healing design in which each node is interconnected via dual fiber rings. In 2001, Cox created its own OC-48 nationwide IP backbone for its customers' Internet data traffic. The company is now evaluating the use of this network to carry long distance voice and video traffic over this IP network. In the future, Cox plans to add networking capabilities to provide services to business customers, use new DOCSIS standards to provide better service control, utilize DWDM to increase bandwidth capacity, and add Resilient Packet Ring technology in some regions.
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