Open Mic - Taking fiber deeper into the network

Wed, 01/02/2013 - 1:08pm
Johnny Hill, chief operating officer at Clearfield

Fiber gives MSOs options.

Johnny HillMSOs were reaping the benefits of installing fiber deep in the network for hybrid fiber/coax back in the 1990s. In most cases, nodes only required two fibers, including one if using WDM technology to combine the forward and return path. Most MSOs deployed 12 fibers to each node as the cost difference from a two-fiber cable to a larger-count cable was the difference of pennies. This forward-thinking attitude is now paying dividends.

There are a multitude of different options for MSOs to leverage their existing assets. The following strategies leverage these deep fibers and existing CMTS and other headend DOCSIS-compatible equipment.

Node segmentation
Innovative electronics manufacturers provide node cases that can contain multiple nodes in each case. When a serving area becomes starved for bandwidth, a second, third or fourth node can be integrated into the existing case, thus reducing the number of customers per node. If there are not any spare fibers at that node, WDM technology can be utilized to create additional capacity on the existing fibers. Typical CWDM applications will allow up to four nodes per case, as modular optical components can support node segmentation in these environments. Dependent upon your environment, multiple packaging options may be required. Look to equipment suppliers that support a variety of deployment options from LGX chassis-based approaches to ruggedized discrete options that can be terminated or hard-spliced for space-constrained environments. Hardened for OSP deployments, these optical component packages will perform in extreme weather conditions while serving today's bandwidth requirements.

Node + 0
Another architecture that benefits from deep fiber is “node + 0.” The node + 0 term refers to a network scheme that eliminates RF amplifiers after the node. Since there are no RF amplifiers in this scheme, this necessitates the need to send the fiber even deeper into the network. Because there are typically 12 fibers at each node, the main node is eliminated, and the 12 fibers will now be branched off to distinct, smaller serving areas. Back at the headend, chassis-friendly packaging can be integrated alongside or separate from terminate-only fiber management elements. Forward and return patch combining power levels can also be conditioned or shaped at the node using the appropriate attenuators to address hot signals.

Perhaps the most intriguing use of these deep fibers is for RFoG (RF over Glass) FTTx applications. Since RFoG leverages existing equipment and can coexist with current HFC networks, it is the ideal choice for MSOs looking to deploy FTTx. As in the previous examples, if 12 fibers are installed to an existing node, the spare fibers can be used to service RFoG FTTx subscribers. If the current node is kept in place (and still uses two of the 12 fibers), there are 10 fibers available for RFoG applications. This equates to 320 fiber-to-the-home customers. These 10 fibers essentially become feeder fibers that can be installed into a fiber distribution hub (FDH). The FDH cabinet will be a central patching and splitting location located near the hub. A node can be decommissioned, and power requirements eliminated in the transport and access network, by delivering those spare or dark fibers down to a more accessible cabinet as feed fibers into an OSP cabinet.

Fiber Deep hubs or hub collapse
Some leading node manufacturers produce node cases that can be upgraded to create a “virtual hub” farther out in the network, without having to build a physical structure or OTN cabinet. By adding amp and switching components, the node case can now serve as a full-service hub that can accommodate up to 32 HFC nodes with only three fibers. In certain applications, a small hub collapse cabinet (HCC) can be pole- or pad-mounted next to the virtual hub to provide enhanced connectivity for fiber terminations and housing optical components. Appropriately designed, an HCC reduces service turnup or maintenance by placing these types of activities on the ground or at a more accessible pole placement. Further costs are saved, as lower-skilled technicians can perform this work as booms, permits or access to pole costs are minimized because the more frequent MAC work (moves, adds, changes) are performed at a lower labor rate. The higher-priced and more sensitive electronics remain untouched and in a secure location up on the pole or strand.

As you can see from the above examples, there is a lot of tread left on the tires in the fiber portion of some existing HFC networks. MSOs that thought ahead and deployed additional fibers in their plant have many options for maximizing the capabilities of those fibers and existing equipment.

Email: jhill@clfd.net

Next month, ThinkAnalytics founder and CTO Peter Docherty will write about leaving money on the table and why the smart money is on personalized recommendations for live TV.


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