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Benefits of Remote PHY

Compatibility with any IP network architecture at the higher layers, future-proofing by increasing the network’s modularity and ease of transition from existing CMTS architectures are a few advantages of working with Remote PHY as DOCSIS 3…

By Francisco Gastiazoro

TL;DR

Compatibility with any IP network architecture at the higher layers, future-proofing by increasing the network’s modularity and ease of transition from existing CMTS architectures are a few advantages of working with Remote PHY as DOCSIS 3.1 establish.

Key takeaways

  • DOCSIS 3.1 supports higher bandwidth than ever before, up to 192 MHz downstream.
  • Actually getting that throughput depends on many things being right.
  • A poor S/N ratio will drag speeds down to not much more than the older protocols.

DOCSIS 3.1 supports higher bandwidth than ever before, up to 192 MHz downstream. Actually getting that throughput depends on many things being right. A poor S/N ratio will drag speeds down to not much more than the older protocols. Changes in network architecture can help achieve the blazing speeds which DOCSIS 3.1 promises.

CableLabs Summer Conference 2018 is around the corner. In collaborationg with Casa Systems, we ‘ll be presenting our orchestration PoC on virtual Converged Cable Access Platform (vCCAP) and Remote PHY. Meet us there!

Distributed access architecture

One of these changes is moving from linear to digital HFC. Digital lowers the S/N requirement, requires less power, and can travel a longer distance without a relay. However, DOCSIS is designed for linear HFC. Several ways of adapting networks to digital HFC are under consideration. All of them involve some form of distributed access architecture (DAA), moving some of the functionality closer to the network edge. Remote PHY is attractive because of the relative simplicity of its approach and ease of deployment.

PHY hardware implements the physical layer (layer 1) of the OSI model. Remote PHY means moving its functionality from the CMTS headend to the edge of the network. It’s fully compatible with DOCSIS protocols. The connection between the CMTS and the PHY can use any implementation of layers 2 and 3.

The Remote PHY specification provides for compatibility among manufacturers’ products, so operators won’t be locked into a vendor.

The advantages of Remote PHY include:

  • Compatibility with any IP network architecture at the higher layers.
  • Future-proofing by increasing the network’s modularity.
  • Ease of transition from existing CMTS architectures.

Alternative approaches to DAA

Remote PHY represents a relatively small change to architectures based on linear HFC. Other approaches decentralize the CMTS more radically.

Remote MAC and PHY move the MAC portion of the architecture, which covers layer 2 and part of layer 3, to the network edge. This is a more complex approach, splitting the DOCSIS functionality between the centralized and remote portions. While it’s a logical continuation of Remote PHY, it may be too radical a change to gain much support in the near term.

Even more decentralized is Remote CMTS. Instead of a large, single CMTS, there is one at each remote node. In a sense, this is less radical than Remote MAC since it keeps the whole CMTS together. However, it means shifting system management to a lot of remote nodes instead of one local one. Among other things, this raises a new set of security concerns.

For the present, Remote PHY by itself looks like the leading candidate for DAA. It’s currently available, while the alternatives are still theoretical.

What it Means for Telecom Operators

The obvious benefit of Remote PHY is speed. Delivering less bandwidth than DOCSIS 3.1 promises would put a telecom operator at a competitive disadvantage. The question of how best to achieve it depends on the operator’s situation.

The architecture doesn’t require moving PHY hardware out to all the nodes in a single step. A combination of local and remote PHY locations won’t present any problems.

The simplest approach is to connect the remote PHY device (RPD) directly, in a port extender configuration. The RPD is still physically close to the central CMTS rather than to the customer. This is the first step in decentralization and allows more coax connections.

Placing the RPD in truly remote locations, closer to the customers, will gain a bigger advantage, but it requires deploying fast digital fiber connections to the nodes. Moving the PHY connections out can be a gradual process, spreading the cost over time. Areas with a high concentration of customers will deliver the largest benefit for the least new cabling, so they make good pilot sites.

Moving to Remote PHY is a significant project that requires careful planning. The benefit of it is that it will let telecom operators deliver higher speeds over DOCSIS, allowing more services and producing greater revenue.

CableLabs Summer Conference 2018 is around the corner. In collaborationg with Casa Systems, we ‘ll be presenting our orchestration PoC on virtual Converged Cable Access Platform (vCCAP) and Remote PHY. Meet us there!

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