Challenges in Deploying Remote PHY

Customers are demanding higher data rates. Remote PHY will let telecom companies achieve them by moving the QAMs closer to their sites. At the same time, any kind of distributed access architecture (DAA) will present some challenges. Being aware of the issues in advance is important to an orderly deployment and to the ability to deal with maintenance issues.

Compatibility with any IP network and future-proofing are a few advantages of working with Remote PHY as DOCSIS 3.1 establish. Learn more on our blog post Benefits of Remote PHY.

Access

The most obvious issue is physical access. While RPNs include diagnostic capabilities, there are times when hands-on troubleshooting and service will be necessary.

Having as much equipment as possible in a central location has advantages for maintenance. An RPN might be located miles away from the central office. It might be in an outdoor location which is inconvenient to reach. Maintenance teams will need to include travel time when they need to service the nodes in person, and they’ll need to have mobile service toolkits.

The deployment of Remote PHY has to strike a balance between bringing service close to the customer and being able to handle the maintenance issues. Expanding too quickly not only is expensive but could create logistical issues which the maintenance team isn’t ready to handle.

Provisioning

The provisioning of customers’ on-premises equipment isn’t significantly changed. IP addresses are still assigned from a central DHCP server. Customer-specific parameters can be set up by the operator (pre-provisioning) or as part of the customer’s online registration procedure (auto-provisioning).

The main concern is that the remote PHY node needs to be secure against tampering even if it’s in a location that isn’t physically secure. The Cable Labs specification requires RPNs to authenticate with the CCAP, guarding against man-in-the-middle attacks. Firmware updates are installed by a secure procedure.

Hands-on tampering is one of the most difficult attacks to guard against, but the Remote PHY specification includes strong protections against it. Dishonest people will try anyway, and it will be important to keep the CCAP and remote nodes updated with the latest security patches.

Quality of service

Remote PHY improves bandwidth and quality of service by shortening the distance for the RF connection, but the increased distance for the Ethernet connection requires some attention. Specifically, the latency to the RPN needs to be low and consistent. The quality of the Ethernet connection to the RPN is critical. The longer the path, the more of a challenge that will present.

The Remote DEPI specification deals with the pseudowire connecting the CCAP to the RPD. It specifies requirements for buffering and allowable skew, as well as specific requirements for UDP and MPEG-TS. Installations need to meet its requirements in order to ensure acceptable quality. Among other things, this means keeping the number of network hops within limits.

DOCSIS 3.1 includes Active Queue Management, which selectively drops packets to maintain a consistent data rate. This helps to avoid latency problems when TCP pushes the data rate up to unsustainable levels. The limited dropping of packets signals TCP not to increase its data rate further when the buffers are close to full.

The demands of DOCSIS 3.1

One of the major reasons for adopting Remote PHY, of course, is to meet the higher throughput standards of DOCSIS 3.1, and in particular to enable full-duplex communication. Shorter coax distances are not only an advantage but a competitive necessity. As the network becomes more extended, it has to improve the quality of the data path at every step.

The move to Remote PHY, or any other form of DAA, is a major change for cable networks. Deployment and maintenance will require more field work. Change is an inescapable part of data and video networking, and these changes will open up vast opportunities to the providers that deal with it best.

Compatibility with any IP network and future-proofing are a few advantages of working with Remote PHY as DOCSIS 3.1 establish. Learn more on our blogpost Benefits of Remote PHY.

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