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Remote PHY

Remote PHY is a part of the Distributed Access Architecture (DAA) family of standards released by CableLabs. It allows the traditional CMTS to be broken up and have the physical (PHY) modulation/demodulation components moved closer to the network’s subscriber.

This function will typically be handled directly in an HFC node in the field or a “shelf” type unit located in a hub or cabinet. The new connection between the CMTS and the Remote PHY Device (RPD) is traditional Ethernet.

Why Remote PHY?

Remote PHY is a technology that needs to be looked at for its ability to solve business challenges, in conjunction with other topics like HFC architecture planning and marketing, to make a difference in the network.

It does this not always direct, but instead sometimes taking a roundabout way of showing its value. It is a technology that can drive massive efficiency in the confines of the CMTS portion of the network and beyond.

Basic Business Challenges

Let’s look at some fundamental business challenges that Remote PHY can potentially bring all or part of the solution to:

  • Customer demand for higher bandwidth offerings drives;
  • Need for Node splits or;
  • Need for new/updated CMTS with DOCSIS 3.1; both of these drives;
  • More items like IP Addresses, RF lasers & receivers, combining networks and racks which drives;
  • Need for more space, power, cooling, etc.

While the items above may sound like what we have always been doing, we need to realize that if we want to achieve solutions to the challenges more efficiently and economically going forward, we need to change the way our architectures are built.


Network Fusion

No matter what your business challenges are today or will be in the future, Remote PHY can likely help you accomplish your goals. However, as noted previously, it requires stepping back and looking at your network as a whole to see which exact implementation will be best for you. No longer can you make decisions in the traditional silos of IP, CMTS, and Outside Plant networks, but rather a requirement to develop master plans that bring them all together for the largest mutual gains.

With many operators already seeing the benefits of Remote PHY, why not find out how it can help you overcome your business challenges and build the winning network?


Our Example Scenario:

Take the case of a rural operator with multiple serving territories covered by multiple Headends/hub sites. Typically, each of these sites would end up with its own CMTS due to distance limitations of both RF Optics performance and the DOCSIS protocol. Many times in the past, we might have been able to get away with smaller CMTS at these locations due to a lower bandwidth demand.

If we want to start slowing down expensive and time-consuming node splits by employing a forward-looking technology that is more efficient with our RF spectrum like DOCSIS 3.1, that may require deploying a brand new, potentially more enormous CMTS that is capable of the protocol. This could become quite expensive depending on how many subscribers we have at each hub. What if, instead, we could centralize the functions of the CMTS and use nearly any type of IP network to interconnect to the sites to produce the DOCSIS carriers via an RPHY shelf? If we can connect the sites by an existing network, leased wavelength, or even a data circuit, we can run Remote PHY.

From this example alone, we can see the benefits of hardware reduction, power savings, support cost reduction, and operational ease of only having a single CMTS. A single CMTS also means IP Address reclamation due to having a single router now handling all the locations. Not to mention achieving the goal of deploying the more forward-looking technologies you set out to do, which may have otherwise been too costly.

On top of this example, here are a few more benefits that we can see from Remote PHY:

  • Taking the RF QAM generation out of the CMTS turns the platform into an IP in and IP out piece-of-equipment. This typically allows the CMTS platform to handle more bandwidth through it if it has the proper backplane and processing capability. This, in turn, allows an operator not to deploy as many individual CMTS units as in the past, thus saving valuable rack space, power, cooling, and shared control hardware along with management time and support and maintenance contracts.
  • By moving the PHY layer of the CMTS potentially out to the node, you can have a compounding effect on how much more efficient DOCSIS 3.1 is. DOCSIS 3.1 will run at higher modulation orders when SNR gets higher. (See our DOCSIS 3.1 page) When you take out any or all of the specific RF Optical link and turn it into a digital IP link, you end up removing a sizable component of the SNR, which can, in turn, lead to the higher modulations due to having a “perfect” RF DOCSIS signal now being transmitted directly from the node. Thus, having the capability to push more data through the same amount of RF spectrum as before. This also reduces your OSP staff’s strain as subscribers are less likely to notice problems before your teams can clean them up.
  • When looking at making an outside plant architecture change of cascade reduction of anything smaller than what the operator has today down to Node + 0, the potential number of transmitters and receivers needed could become overwhelming from a space and powering standpoint. In contrast, Remote PHY uses high-density Ethernet switching in place of an RF combining network and the Ethernet links in place of the RF optical links. This offers the potential to reduce significantly the space considerations needed.

There are a few other benefits of using Ethernet as the transport for Remote PHY. The first can now potentially mesh the RPHY transport into an already existing long haul or metro IP network. This can allow for an excellent efficiency of getting two benefits out of the same IP transport network instead of managing two distinct optical networks in a world where free fibers are not always in ample supply.

The second benefit of using Ethernet is gaining the potential for genuine redundancy further out into the network due to many IP protocols’ resiliency. Lastly, this technology does not require a complete outside plant upgrade like many unfounded rumors have perpetuated. It can be completed before or after any planned plant architecture changes based on when your strategic plan calls for it.

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