Switched digital video over DSL currently appears to provide a better return-on-investment (ROI) than competing architectures, according to Frank Wiener, VP of Business Development at Calix. Speaking at this week's NFOEC conference in Orlando, Florida, Wiener described an ROI analysis of video delivery over DSL and FTTP that his company has performed. Calix analyzed all 550 COs in Michigan to understand the revenues and costs involved in offering video services. Calix created a model to compare various architectures to deliver video over this existing network, and projected the incremental costs to change the network, as well as incremental revenues. In high density and moderate density COs, the results showed that the best Net Present Value (NPV) and lowest up-front cost came from the delivery of three channel switched video over DSL. The forecast assumes delivery of two standard definition channels and one HDTV channel. The analysis found that PON also provides a positive NPV, but requires more up front expense. In small COs, it was "difficult to make the numbers work" with either technology. Wiener added that if the delivery of more than one HDTV channel is important, it would make PON more attractive. He feels that FTTP holds great promise in high density markets, but their analysis found its return lower than further buildouts of DSL. Using a DSL network to deliver video initially, followed by a later transition to PON as customer requirements change, may make the most economic sense.
A CWDM overlay on an EPON system offers the advantages of the power splitting PON architecture combined with wavelength security and component economics of CWDM, according to Paul Dickinson of OFS. The architecture offers high capacity metro access combined with low cost PON for outside plant sharing, and allows service providers to offer dedicated wavelength services for businesses. OFS has demonstrated the compatibility of CWDM overlay with Gigabit PON access carrying both digital and analog transmission over distances of 20km. The test found that the CWDM approach saved up to 25% compared to DWDM and enabled the same service delivery.
Ross Halgren, VP Network Architecture for RBN agreed that CWDM and PON are complimentary. During the last ten years, fiber loops have been deployed closer to end customers in order to provide DSL. As a result, today fiber can often be split into greater numbers of PON access connections at the cabinet (64 instead of 32) because there is less loss from cabinet to customer. CWDM can be used to deliver a wide variety of services to the cabinet, from which the signal will be carried by PON to customers. Each CWDM wavelength can be used to deliver a different type of service and different protocol.
The delivery of analog video over a PON network is more challenging than delivering digital video, according to Frank J. Effenberger of Quantum Bridge Communications. Analog video overlay on PON is feasible with current technology, but the outside plant must be carefully designed and constructed to insure minimum loss variations. Multiplexed analog video is a fragile signal. Video overlay signals are generally quite strong, but they can result in overload, and the signal degrades as it passes through the network. In planning for analog, network planners must account for layout variations, and the loss introduced by individual components the signal will pass through.
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