A New Approach to Driving IP Deeper into HFC Networks



Aurora Networks’ Node QAM Architecture Lowers Barriers to All-IP Migration

By John Dahlquist, Dawn E. Emms and Rei Brockett

With the advent of advanced services and steady progression to all-IP delivery, cable operators are increasingly drawn to the idea of evolving to an IP-optimized network infrastructure as a means of increasing operational efficiencies and lowering the costs of expanding channel counts and services. In addition, they recognize the migration to an all-IP network offers a unique opportunity to greatly reduce the costs and time associated with deploying next-generation services to serve both current and future needs.

While the all-IP migration is moving at a pace of its own, many vendors and operators feel that even with the progress made in the underlying technologies, it is only now starting to advance. And just what the correct next steps should be remains unclear in many instances.

AuroraWith the accelerated growth of IP technology, two main challenges have developed for operators. The first challenge is posed by the strong increase in narrowcast requirements such as SDV (switched digital video), time-shifted TV programming, video on demand (VoD) and continued growth from advanced bandwidth-hungry services such as HDTV and 3DTV. Further, operators need to allocate more capacity for DOCSIS 3.0 services given the increasing reliance and drive for higher-speed data. In addition, there is discussion about IPTV migration strategies that will utilize narrowcast bandwidth to deliver an ever-increasing volume of premium content to hybrid set-top boxes.

Second, the path is unclear for operators migrating to an all-IP environment. Operators are challenged with how the transition from traditional MPEG transport to IP-based distribution of video content will occur. They are continuing to evaluate methods to stream services in pure IP mode, especially when dealing with the process of simulcasting the same content in IP that is delivered over MPEG. There continue to be debates over distribution methods, such as varying approaches to IP delivery. Disparities in individual operators’ architectures make a one-size-fits-all solution nearly impossible.

The Node QAM Solution

As cable operators look to address these problems and switch to all-IP networks, as with any new deployment, there are steps and processes which can be implemented in order to ensure their migration is seamless. Notably, a solution that moves the edge QAM functionality into the node (node QAM) enables cable operators to make the initial step in migrating toward an all-IP environment.

This transitions the traditional HFC plant into a digital HFC network. In essence, by locating the RF modulation processes at the point of signal conversion from optical transmission to RF transmission over coaxial cable, node QAMs can be employed to greatly enhance the flexibility and cost efficiency of service migration. Functionalities associated with the node QAM architecture operate independently of and in parallel to legacy QAM processes, ensuring that the new architecture can be implemented without disrupting existing operations or straining capital investments in headend equipment.

Node QAM architecture removes the need for uniform allocation of QAM channels across all service groups. Operators can dynamically change the mix of digital narrowcast and broadcast services delivered over a given channel on a node-by-node basis without requiring adjustments in the headend RF combining network or rebalancing the HFC plant. At the same time, they can dynamically change utilization of wavelengths so that any given wavelength carrying any mix of content can be assigned to serve just one node or shared across multiple nodes.

All the processes above the PHY layer associated with each remotely modulated service stream, such as encoding, statistical multiplexing, encryption, SDV, ad insertion, IP formatting and fragmentation for adaptive streaming, are performed separately at the headend or hub prior to multiplexing of all the streams onto a digital optical link to the node.

The node QAM is a highly flexible alternative to existing options that may prove to be the best course of action in many instances. To merit serious consideration, it must be a non-disruptive solution that easily lives alongside existing QAM infrastructure and operations, while providing a means of introducing a more cost-effective way to expand services over time.

AuroraKey Advantages

Some of the advantages that node QAM technology brings to operators include:
Maximum Channel Flexibility: To meet this criterion, a node QAM solution should provide a very flexible means of using remote QAM resources both to accommodate the addition of new QAM channels beyond those already supported by legacy QAMs and to retire legacy QAMs to whatever degree and at whatever pace the operator chooses. This means that node QAM modules must match the port density criteria set for next-generation universal edge QAM and CCAP implementations with the ability to deliver up to 158 QAM channels over the full downstream spectrum up to 1 GHz.

Operators must be able to remotely assign channels to be modulated by node QAMs with complete flexibility to change those assignments over time. QAM modules must be designed to plug into a vendor’s strand- and pedestal-mounted node housings with all the interfaces required to tap into the node power supply, performance monitoring system and other OSS resources, including, of course, the remote QAM management system.

Universal Service Multiplexing: By definition, the use of node QAMs means that signals are multiplexed and delivered digitally from the headend. The multiplexing and configuration processes should be able to operate across the entire downstream payload to dynamically support on-the-fly assignments of any mix of digital content to any given QAM channel at any given node, including broadcast, HDTV, SDV, VoD, nPVR, cable IPTV, digital voice and DOCSIS data streams.

The architecture should allow all processes above the PHY layer to be performed independently so that every service stream multiplexed into the optical distribution network is appropriately encoded, encrypted and otherwise groomed for the receiving device with all advertising content and interactive prompts and triggers embedded in the stream. In other words, the mechanics of the node QAM must be completely agnostic to the services running through it.

Wavelength Flexibility: At the same time, the headend multiplexing platform should be able to assign and dynamically change assignments of wavelength resources on the fly in multiple ways such that:

  • Any given wavelength can be employed to deliver a complete or partial lineup of broadcast digital TV channels to multiple nodes.
  • Any given wavelength bearing narrowcast content can be shared across multiple nodes, enabling QAMs at each node to modulate only those streams that are targeted to subscribers in the node service area.
  • The full complement of broadcast and narrowcast signals to be supported by node QAMs at any given time can be provisioned over a single wavelength to each node.

Such dynamic provisioning flexibility allows the operator to incrementally utilize node QAM resources cost effectively without having to forecast in advance what the eventual mix of streams will be at any given node or on any given QAM. There’s no need to pre-wire or alter wiring of the RF combining network with every change in the service mix insofar as the mix can be dynamically shaped and expanded over time on a neighborhood-by-neighborhood basis.

This flexibility means operators can put node QAM resources to use incrementally, at whatever pace suits their needs. For example, an operator may want to dedicate a block of spectrum capable of delivering one hundred narrowcast or SDV streams to node QAMs but, at the outset, may only need to use a single QAM to modulate ten streams at any given node. In this case all 100 streams could be delivered over a single wavelength to ten different nodes where each QAM would be assigned to modulate whichever group of ten streams is targeted to its service area. In the future, as more streams are dedicated to each node within the original block and more blocks are added, wavelength loading and QAM assignments for node QAM resources can be orchestrated to precisely align with the operator’s strategic migration goals.

Exploiting Digital Optics: Implementation of digital optical transmission is fundamental to the flexibility made possible by a node QAM architecture insofar as all wavelength assignments can be implemented without requiring resetting of power levels and end-to-end balancing for changes in distances that are required with analog optics. While operators will continue to employ analog transmission to deliver channels modulated by legacy QAMs, all streams assigned to node QAMs will be delivered via low-cost, small form factor, pluggable optical transmitters.

Use of digital transmitters in the downstream, mirroring the digitization of upstream optical signals now widely used with HFC node platforms, will also serve operators well in their efforts to maximize bandwidth over the existing cable plant. Any payload delivered digitally to the node will avoid the losses incurred through traditional RF combining and optoelectronic conversions resulting in signal-to-noise output at the node that is on par with today’s headend outputs in the range of 40-42 dB with attendant improvements in harmonics and noise floor performance. These gains open the possibility of expanding available bandwidth on the coax by going to modulation above 256 QAM on the node QAM-modulated channels.

Overcoming Space and Power Consumption Costs:
With all the flexibility that comes with the use of node QAM architecture, operators also achieve another key goal in the migration to higher QAM counts, which is the ability to reduce power costs and conserve space in headends and hubs. Finding a way to minimize QAM rack space consumption has become an urgent priority in many cable facilities. While node QAMs will incrementally add to power consumption at the nodes, the option offers a net power savings compared to the costs associated with supporting QAMs and analog optics, maintaining temperature stability and providing backup power in headends and hubs.


The growing number of narrowcast channels required to meet today’s market demands has presented significant challenges within both service and transport layer architectures. With the imminent transition to an all-IP network, cable operators have the opportunity to take advantage of the innovative technology presented here, helping them to simplify the migration process. Ultimately this will enable them to maximize the benefits that come with driving IP deeper into the network.