Why Do Nodes Need to Be Split?
Currently, there are many hundreds and often more than a thousand homes passed per node, which is up to ten times higher than what is desirable for a happy customer base. To provide high-speed Internet access, an inexhaustible library of VOD choices, eye popping HDTV service, and a wide range of telephony options there should be as few as a hundred homes per optical node.

Fiber Starvation
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 between hub and nodes. Installing new fiber can be prohibitively expensive and time-consuming, with costs up to $20,000 per mile. MSOs don't have the time or the budget to lay new fiber where the better solution for node splitting exists.

DWDM Alternative
Using node splitting in combination with dense wavelength division multiplexing (DWDM) allows the operator to increase the bandwidth capacity and offers pay-as-you-go expandability. Passive DWDM components enable multi-step network upgrades, starting from as few as only one or two new nodes. Consecutive upgrades will not require any service disruption. The key enabler is the fact that DWDM technology allows the transmission of multiple wavelengths, or "colors" of light over the same fiber, using the 1550 nm band without interfering with existing legacy 1310 nm traffic.

Network Architecture
A variety of HFC network architectures are deployed nationwide. Most hub-to-node links use legacy 1310 nm technology, but some use 1550 nm. Broadcast and narrowcast signals can be transmitted over the same fiber, or using separate fibers. Confluent Photonics' DWDM node splitting can be implemented with virtually all existing HFC configurations. In certain instances, the MSO can even free up the traffic-bearing fiber and use it for other services!

Before the Upgrade
As an example, the MSO can increase the number of nodes in a two-fiber, hub-to-node legacy 1310-nm system as shown in Figure 1. The existing network uses one fiber to transmit broadcast and narrowcast downstream channels to the node, and the second fiber for the return traffic to the hub. The distance between the hub and the node is limited by the power budget of the 1310 nm lasers and receivers (usually up to 25 km).

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

After the Upgrade
The upgrade solution uses HMD-16-200 Hub DWDM Mux/Demux and SNS-16-200 Strand Mounted DWDM Node Splitter as shown in Figure 2. This passive optical equipment overlays eight forward path and eight return path 200 GHz DWDM channels in the C-band (1530 - 1565 nm) and 1545 nm broadcast window over 1310 nm legacy fiber.

In the upgraded system, the first fiber between the hub and the node remains intact - it still carries forward broadcast and narrowcast 1310 nm traffic. The other fiber became bi-directional: it now delivers the legacy 1310 nm return, as well as the DWDM QAM forward path, and DWDM digital return. In addition to that, it carries 1545 nm 'purple band' analog broadcast to the new nodes.

Figure 2*. Up to eight new nodes can be added to the legacy fiber plant with Confluent DWDM equipment.

* Patents pending

After the initial installation of the passive optics, up to eight new bidirectional DWDM nodes 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 nodes.

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.