Monday, October 15, 2007

Motorola's E-CWDM Extends Cable's HFC

A number of tools have emerged to help the cable companies extend the life of their Hybrid Fiber Coax (HFC) networks in the face of strong new competition from FTTH and FTTN networks. The basic problem the cable companies have is to support more HD broadcast services at the same time as they are expanding both their SD and HD narrowcast services. (A narrowcast service is one such as video on demand that delivers content to a single viewer.)

A cable HFC network uses fiber to connect a hub office to an optical node that typically connects to about 500 homes today. One of the ways that a cable company can do this is to reduce the homes served by an optical node. They can do this by stacking up optical nodes. They can use four optical nodes, for instance, connected by four fibers and supporting 125 subscribers each. Motorola offers a modular approach so that the four fibers can be connected to a single box which then splits the bandwidth to four separate groups of 125 homes each.

Motorola's new E-CWDM system uses coarse wave division multiplexing that uses five wave lengths to carry the equivalent of five separate fibers to the optical node. If all five wavelengths are used, then each wavelength can then serve a separate group of 100 homes.

The advantage of ths approach is that it conserves fibers. Often the cable company does not have four or five pairs of fibers running to each optical node. Even if the fibers are there, the cable company may prefer to reserve them for business services, for example.

The E-CWDM optical node is about twice as expensive as an optical node that can connect to an equivalent number of fibers. However, this is much less expensive than running new fiber, so it is an economical approach in many cases.

E-CWDM will be useful to cable companies as a way to extend the life of their HFC network. They have other tools that they can use as well such as expending the spectrum used, switched digital, IPTV, and cable PON.

As useful as these tools will be, however, they will not eliminate the need for cable companies to move to a FTTH architecture in the future in order to match strengthening telco competition.

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