Doing the Splits – How DAA Enables Ongoing Node Splits
Advanced Upstream Blog Series Introduction
In the Advanced Upstream blog series we will explore how cable operators have traditionally managed upstream bandwidth capacity planning, how market dynamics and technical innovation are driving changes, and where things are likely headed in the coming years. In this entry we will discuss the “more Nodes” approach – how to shrink service group sizes via node segmentation/splits.
“More Nodes” Introduction
Node splits have been the default plan for reducing upstream and/or downstream service group sizes, and while they are a reliable way to increase capacity they create problems. In addition to the fiber construction activities in the outside plant, each fiber terminating at the hub or headend may require optical receivers/transmitters, splitters/combiners, and of course CCAP ports. As hubs and headends reach capacity from both rack space and power/cooling capacity standpoint, operators must do things differently to continue splitting nodes. Enter distributed access architectures (DAA) like Remote PHY and Remote MACPHY. With DAA, at least the PHY layer is moved out of hubs/headends into the field, alleviating the previous constraints but creating new challenges. Remote PHY gained traction as specifications for it were locked down early and incumbent NEM’s brought the first solutions to market. More recently Remote MACPHY is gaining traction, especially with the Flexible MAC Architecture (FMA) work by CableLabs. Long term, there will not be a dominant variety, each has its strengths and operators will benefit from having choices.
Other DAA Benefits
Besides the obvious benefit of enabling continued node splits, there are several other benefits that DAA brings to the party:
- Digital optical link replaces analog – Commodity 10G optical Ethernet links are cheaper to install and maintain over time, and provide a few dB better SNR vs unique-to-cable analog links.
- 10G optical Ethernet in the access network – In addition to serving DAA nodes, the 10G optical Ethernet links can also be used to spawn Remote OLT connections for PON services, support small cells for mobile services, and potentially support SMB services. This benefit can’t be overstated, it is truly a game-changer for cable operators.
- Overall architecture flexibility – Especially with the recent FMA specification work, increased virtualization will be possible putting specific functions wherever needed to best support future services and use cases
DAA deployment is not without challenges ranging from operational/maintenance, technological, and even organizational issues. As network functions are deployed out into the field, clear lines of demarcation for functions become blurred and troubleshooting must involve groups who didn’t previously talk, creating organizational challenges. Listed below is a subset of the deployment/maintenance challenges facing operators, many more can be found at viavisolutions.com/daa.
Removal of RF from hub/headend – All DAA variants move the PHY layer out into the field, removing the test/insertion points needed for return path monitoring, forward and return sweep, and signal leakage. Solutions vary for each function, but they all share the common element of using the RPD as a virtualized probe/transmitter replacing dedicated hardware. Some of these solutions have been engineered to use the same deployed sweep and leakage meters and established workflows for both legacy and DAA nodes, minimizing disruption to established workflows and processes for technicians. Another key to operational success is ensuring solution interoperability between DAA NEM’s – DAA Test-Ready solutions!
- Return path monitoring – Systems exist to receive inputs from monitoring hardware like PathTrak and interface with RPD’s via distributed interface servers. These systems can non-intrusively provide the highest sample rates from CCAP/RPD’s while presenting a common user interface to Tech’s whether they are working on a legacy of DAA nodes.
- Sweep – Sweepless sweep has generally been accepted as a substitute for traditional forward sweep, but for return amp alignment and balance the responsiveness of traditional return sweep is still highly desired. A solution exists to use deployed field meters and existing sweep processes leveraging the RPD as the sweep receiver and telemetry transmitter. This solution is ideal for troubleshooting outages even when services are down and amp alignment and balance. When fast responsiveness is not required return sweepless sweep is another option.
- Signal Leakage – Leakage systems have also leveraged the RPD to generate signal tags, and modern leakage meters can detect OFDM pilots without any type of tag being transmitted.
Video Verification – RF video is created for the first time at the RPD, and given that each service group may have unique configurations there is a lot that can go wrong. In addition to typical physical layer problems, you have to check for missing programs/PID’s, stalled PID’s, out of band (OOB) carrier operation, and more. Early adopter operators would load up a truck with a variety of set top boxes and a monitor, run a temporary drop down to the truck, and manually flip through the channels to check each program on each node. Recently field meter-based capabilities exist to automate this testing and shrink test times from 30 minutes or more per node to 5 minutes.
Fiber Deployment and Characterization – Many DAA roll-outs drive the deployment of new fiber, and existing fiber that is to be reused must be characterized to ensure fitness for use in 10G applications. Just because a fiber deployed 15 years ago has worked with analog lasers doesn’t mean that it will support 10G or higher applications going forward. The other fiber-related challenge is just the expansion in the overall amount of fiber deployed. Many MSO’s previously had a few fiber experts on staff, all fiber issues would be deferred to them. Now many more tech’s must be equipped and trained to deploy and troubleshoot fiber issues.
Many, Many More – Deployment of DAA is an expansive project involving many different competencies and workgroups, each with their unique challenges. viavisolutions.com/DAA is an excellent resource to see more examples.
DAA is rapidly becoming a popular option for operators looking for more upstream bandwidth, but it is not the only option in use. Stay tuned for future blog postings on the other common options and how they all work together to keep cable operators ahead of the upstream demand curve.
Want to learn more? Listen to the Broadband Lounge Podcast Series or visit the VIAVI Advanced Upstream Page for more information.
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