Business Opportunities for MSOs
The large demand for business-to-business data traffic is primarily served by the local phone company at fairly hefty monthly charges for very modest bandwidth service. This provides a sizable opportunity for cable MSOs. The existing fiber infrastructure passes near many of these businesses, but often there is no spare fiber to serve them. If the existing HFC network could be employed to provide point-to-point links between businesses, then an extremely lucrative revenue source would become available.

Fiber Exhaust: Where Did All the Fiber Go?
Some networks enjoy a glut of installed fiber, but these networks are few and far between. In many places there is a known shortage of fiber. In many other places, it's even worse: operators don't know if they have a problem until they go looking for unused fiber in their networks. They don't always have all the fiber they thought they had. Fiber shortages result from a variety of maladies, including breakage, and hostile takeovers of fiber to serve new networks.

DWDM Alternative Saves up to $20,000 per Mile over New Fiber Installation
Installing new fiber can be prohibitively expensive and time-consuming, with costs for the fiber alone up to $20,000 per mile. Most of the existing HFC networks use only a single wavelength, usually 1310 nm to deliver signals to and from the optical node, as shown in Figure 1. The bandwidth of existing fiber is being vastly underutilized with fibers often carrying only a single wavelength in a single direction. Dense Wavelength Division Multiplexing (DWDM) components added to the existing HFC infrastructure enable an MSO to use the "hidden" bandwidth instead of laying new fiber. Nothing is wasted. Confluent's DWDM equipment combines new traffic with legacy traffic, in both directions. The key enabler is the fact that DWDM technology allows the transmission of multiple wavelengths, or "colors" of light in the same fiber, in the 1550 nm band, without interfering with the existing 1310 nm wavelength.

Figure 1. A typical HFC hub-to-node link uses 1310 nm transmitters and two fibers.

Network Architecture
An example of delivering business services using a combination of HMD-20-200 Hub DWDM Mux/Demux and SMD-20-200 Strand Mounted DWDM Node Splitter is shown in Figure 2. This method works when there are no available spare fibers, and is particularly attractive for providing new business services in a fiber-starved region. In a typical 1310-nm HFC system there is more link margin on the return path than the forward path and there are fewer fiber non-linearity issues to be concerned with. By splicing into the return path with a DWDM Multiplexer/Demultiplexer, a large number of spare optical channels now become available for data services over the existing fiber. The first fiber between the hub and the node remains intact - it still carries forward broadcast and narrowcast 1310 nm traffic. With the Confluent Photonics DWDM equipment installed, up to ten bi-directional ITU channels can be added on an as-needed basis. No service disruption is necessary for additional upgrades. If required, optional EDFAs can substantially increase link lengths in the new business links.

Figure 2*. Upgraded HFC network delivers business services over the legacy fiber.

* Patents pending

Considerations for the Active Optics
Many vendors of Gigabit Ethernet equipment supply small form-factor plug-able (SFP) optical transceivers. These inexpensive transceivers have generous link margins and are now available in DWDM wavelengths. By employing routers and switches that use these SFP transceivers, MSOs can deploy business services and realize rapid ROI. The MSO can add transceivers as needed when a new customer requires service.

How Do I Do It?
At Confluent Photonics, we understand that every network is different and no universal solutions exist in the HFC world. We have an experienced team of experts ready to help you in designing your own HFC upgrade strategy, and in implementing it. We will recommend the necessary equipment and perform calculations to prove that the proposed architecture will work reliably. Call our Technical Support Department at (603) 893-4906, and select option 3 at the prompt.