PDF of this tutorialFigure 3 indicates the typical bandwidth range needed, both forward and reverse, for a number of video, data, advertising, telephony, and multimedia services, assuming a node size of 500 homes and reasonable penetration rates. This figure indicates that the 500-home node will not be sufficient in the long run, assuming analog broadcast cannot be eliminated for some years to come. The goal then is to find ways of economically driving the fiber deeper into the access network.
Figure 3. Determining Node Size
The ability of the reverse or upstream path of HFC networks to handle the full suite of interactive services is the subject of much concern. To address potential performance issues, both Fabry Perot and uncooled distributed feedback lasers (DFB) are being used in networks today, depending on the services being carried. Over 250,000 high-speed cable modems already are deployed in North America, giving large-scale credence to the two-way integrity of the HFC network. The deeper the fiber is deployed, the smaller the ingress problem becomes. Figure 4 shows the loading of the reverse path, given 500 homes passed per node, for three different business models. Unless cable telephony is being deployed, this node size is reasonably sufficient from a traffic point of view. To address the performance dimension, however, as fiber is pushed deeper to handle the forward traffic, the RF cascade length is reduced in length, limiting ingress, improving reliability, and lowering power costs. If the fiber-deeper concept is extended to its logical limit, it leads to a very interesting point, which will be examined next.
Figure 4. The Loading of the Reverse Path
