TECHNICAL
COMPARISON OF HFC WITH TRUE PON
with 48v DC power from a standard telco supply with battery back-up. Eight or more batteries might be required to run on backup for an extended time, or fewer batteries to simply hold the load as a standby generator starts. There would only be up to ten of these sites for our sample 100,000-home system. We will assume that a single remote OLT site, feeding 10,000 homes, consumes 1,800 watts. In practice, the number of homes in the cabinet service area will vary. De-centralised – Remote “Node PON” OLT serves 500 homes This would be the case if we overlay a conventional HFC Node + 6 system with two remote OLTs covering each existing 500-home HFC node location, or with one half of the existing node locations for a Node+3 system serving 125 homes per node. We could use a strand-mount remote “Node PON” OLT fed by a cable power supply or even existing HFC plant power if enough excess power is available. (The power consumption of a typical Node PON OLT is up to about 120 watts.) Because of the lower load, reducing the battery count could be considered. In order to keep comparisons consistent, we will continue to assume six batteries per power supply. If six batteries power a single Node PON OLT, run time in excess of six hours is likely to be expected. Though they may have different names, “Node PON” is available from many of the major HFC node and PON manufacturers, and is an integral part of the “Generic Access Platform” under development at SCTE/ISBE.
With a PON using no field-mounted OLTs, the power and battery cost is zero. So, all of the above can be considered saved expense when comparing PON versus HFC. REMOTE OLT PON In a greenfield situation, we can plan to run enough fibre out of each hub or headend to feed all of the PON splitters. However, we are talking about a brownfield HFC network where we would probably want to use available fibres in order to minimise construction. That would require the use of remote OLTs. Remote OLTs require power, and each conventional cabinet or shelter mounted remote OLT requires substantially more power than an HFC node or amplifier. There are, however, fewer required. While each remote OLT can feed a number of PONs, even more fibre efficiency can be achieved by layering Dense-Wavelength Division Multiplexing (DWDM) to feed several remote OLTs on a single fibre, using inexpensive colourised pluggable optical modules.
Let’s look at two possible architectures for Remote OLT PON.
Centralised – Remote OLT serves 10,000 homes
This approach is more typical of a greenfield architecture adapted to reduce transport fibre counts, or allow for long distances from the headend or central office. Here, the Remote OLT is provided
MARCH 2025 Volume 47 No.1
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