The R-PHY Path to R-MACPHY

Most operators recognize Distributed Access Architectures (DAA) as the future of their HFC network—but the path to that future isn’t as clear. CommScope’s Craig Coogan blogs on how operators can uncover a clear and viable path to R-MACPHY in the future.


Most operators recognize Distributed Access Architectures (DAA) as the future of their HFC network—but the path to that future isn’t as clear.

Until very recently, operators had to choose upfront between R-PHY and R-MACPHY as they planned their DAA solutions. This led them to consider solutions that might not be optimal in the long term or to postpone their network evolution decision altogether. Moreover, inconsistency across network topologies often dictated different architectures in different areas. Add in other factors such as service uptake, density, economics, and market trends—and it become obvious why this was not a simple binary decision.

R-PHY & R-MACPHY Compared

In R-PHY, the PHY layer is moved to the fiber node or to an R-PHY shelf, while the MAC layer is

retained in the hub or headend. This configuration enables the reuse of the physical or virtualized CCAP Core and has slightly lower power consumption in the fiber node. The cost of an R-PHY architecture is lower in the fiber node but higher in the headend, where it requires higher power and more rack space. It also imposes more operational complexity, requiring a grand master clock and timing network—and has higher transport latency, because the MAC and the PHY are separated.

In contrast, R-MACPHY moves both the MAC and the PHY layers to the fiber node. The CCAP Core

function, which handles DOCSIS processing, is in the R-MACPHY device, which now resides in the fiber-optic node, and the digital/RF interface (PHY layer) is also placed at the optical/coaxial boundary. As a result, R-MACPHY is a simpler, all-in-one-box architecture that is much easier to operate. It does not require a CCAP Core and can be deployed without a grand master clock. This architecture provides the lowest latency—making it more appropriate for applications with low latency tolerance. It has the lowest power consumption in the headend, but adds a small amount of power in the node due to the inclusion of the MAC.

Achieving R-MACPHY via R-PHY

Clearly, R-MACPHY presents several key performance advantages over R-PHY—particularly for increasing capacity in the upstream, enabling low-latency applications, streamlining operations, and paving the way to a virtualized operating environment. But, for many operators, R-MACPHY’s greater upfront layout may lead them to choose R-PHY, which can achieve many of the key benefits of DAA while leveraging more of the existing network and headend. For many years, this was a difficult decision to make—but with the availability of CommScope’s new RD2322 R-PHY/MACPHY Device (RxD), operators no longer have to choose.

The RD2322 supports operation either as an R-PHY device (RPD) or R-MACPHY device (RMD), allowing operators to switch between the two modes of operation with a simple software-only upgrade. In RPD mode, the RD2322 handles the PHY layer functionality, leading to alleviated demand in terms of density and power consumption in the headend. In RMD mode, it provides a simple, all-in-one-box distributed CMTS solution that moves both the MAC and PHY layer functions out of the headend/hub to a fiber-optic node. Both solutions place the PHY layer at the optical/coaxial boundary.

Furthermore, the RD2322 supports the major upstream frequency splits, including low-split (42 or 65 MHz), (mid-split) 85 MHz and high-split (204 MHz). The RD2322 simplifies the path to DAA with the solution’s flexibility of deployment, ability to produce higher bandwidth capacity and fiber efficiencies, and simplified plant operations.

In summary, the RD2322 enables operators to make the switch to DAA today, and leverage much their existing network infrastructure, while giving them a clear and viable path to R-MACPHY in the future. To find out more about the RD2322 and the path to DAA, please get in touch or visit our SCTE web page.