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DOCSIS

CableLabs® New Remote PHY Specifications expand DOCSIS® Network deployment options

Karthik Sundaresan
Distinguished Technologist

Jul 7, 2015

DOCSIS technology continues to extend the usefulness of the hybrid fiber coaxial network and increase its global adoption. Distributed Architectures for DOCSIS networks are emerging that provide significant scale advantages and flexible deployment options supporting for both DOCSIS 3.0 and DOCSIS 3.1 networks. Distributed DOCSIS deployments are beginning today in some markets based on the earlier C-DOCSIS specifications.

New Specification Release

CableLabs is documenting several different Distributed CCAP Architectures (including Remote PHY and Remote MAC-PHY) and will release the set of technical reports and specifications throughout this summer.

Last month, CableLabs publicly issued the Remote PHY family of specifications. Theses specifications are also known as MHAv2 as these are an evolution from the original Modular Headend Architecture specifications.

The Remote PHY technology allows for an integrated CCAP to be separated into two components: the CCAP Core and the Remote PHY Device (RPD) and describes the interfaces between them. One of the common locations for an RPD is the optical node device that is located at the junction of the fiber and coax plants, while the CCAP Core stays at the headend. A CCAP core can control and setup data paths with multiple RPDs situated in multiple fiber nodes.

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What is Remote PHY?

The Remote PHY technology uses pseudowires between a CCAP Core and a set of RPDs. The CCAP Core contains both a CMTS Core for supporting DOCSIS data transport and an Edge QAM Core for supporting video transport. The CMTS Core contains the DOCSIS MAC (signaling functions, downstream and upstream bandwidth scheduling, and DOCSIS framing) and the upper layer protocols. Remote PHY supports both DOCSIS 3.0 & 3.1 Specifications. The EQAM Core contains all the video processing functions that an EQAM provides today.

The RPD contains mainly PHY related circuitry, such as downstream QAM and OFDM modulators, upstream QAM and OFDM demodulators, together with pseudowire logic needed to connect to the CCAP Core. The RPD platform is a physical layer converter device whose functions are to convert downstream DOCSIS data, MPEG video and out-of-band (OOB) signals received from a CCAP Core over a digital fiber network such as Ethernet or passive optical network (PON) to analog RF for transmission over the coaxial cable; and to convert upstream RF DOCSIS, and OOB signals received over the coaxial cable to digital for transmission over Ethernet or PON to a CCAP Core.

r-phy-docsis-signaling

The CableLabs Remote PHY technology is detailed by six specifications and one technical report (describing the overall architecture) including:

  • The System Specification that describes System level requirements such as initialization sequences and security.
  • The R-DEPI and R-UEPI specifications that describe the downstream and upstream pseudowires and the L2TPv3 control plane.
  • The GCP specification that defines a protocol used for configuration of Remote PHY Devices (RPD).
  • The R-DTI specification that defines the timing interface between the CCAP-Core and RPD.
  • The R-OOB specification that defines support for the SCTE55-1 and 55-2 out of band data for video applications.

What’s Next?

These specifications define the technology to provide guidance to vendors building solutions for the Remote PHY architecture. Vendors have begun architecting ASIC designs, device platforms and software to implement the RPD and CCAP-Core devices. The OSS requirements for managing these devices are also being specified at CableLabs and will be released as an additional specification later this summer. These distributed architectures of course support standard DOCSIS 3.0 and 3.1 modems and gateways no differently than integrated architectures.

The main options under the umbrella of Distributed CCAP Architectures are the Remote PHY and the Remote MAC-PHY technologies. CableLabs’ work is in progress to document the Remote MAC-PHY architecture. This work will culminate in a technical report which will also be released this summer.

Investigating Distributed CCAP Architectures

The work around Distributed CCAP architectures (DCA) is of interest to many CableLabs members in North America, Europe and Asia. Cable operators are investigating DCA for the various gains they bring including:

  • Maximizing DOCSIS 3.1 Channel capacity
  • Simpler operations with digital fiber/Ethernet transport
  • Higher Efficiency of Digital Optics vs. Analog Optics (wavelengths, reach, cost)
  • Helps hub/headend facilities issues around space, power, and cooling as operators move towards Fiber Deep architectures or consider further Node Splits
  • Consistency with FTTx deployments which will include remote architectures for reach and wavelength management
  • Fits with the SDN/NFV initiatives operators are considering across access networks

These integrated & distributed HFC technologies have parallels, and similar features and benefits, to wireless infrastructure architectures such as Macro-cells, small-cells, Distributed Antenna Solutions, and Cloud-RAN with Remote Radio Units. These Distributed CCAP Architectures fit well in different deployment scenarios and all work cohesively together to support the varying capacity and demand in the areas where their deployments provide the best solution.

As operators look to optimize their network deployments in each of their cable plants in each of their markets it will be very interesting to see how and where these distributed CCAP technologies will be deployed in each operator’s HFC networks. It is indeed an exciting time to be working on the access network technologies and being part of the evolution it is going through.

Karthik Sundaresan is a Principal Architect at CableLabs, responsible for the development and architecture of cable access network technologies. He is primarily involved in the DOCSIS family of technologies and their continued evolution.

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Consumer

Technology Implications of 2Gbps Symmetric Services

Jon Schnoor
Lead Architect: Wired Technologies

Jun 11, 2015

Service providers and municipalities alike continue their push toward offering gigabit services over fiber networks. In fact, fiberville is a web site dedicated to listing which service providers and municipalities provide fiber solutions. Recently, Comcast significantly upped the ante by announcing a 2 Gbps symmetric service that will become available in certain locations. The services announced will be 2 Gbps downstream and 2 Gbps upstream. This is a substantial announcement due to the 2 Gbps speeds and symmetrical services which facilitate faster file uploads which is of interest to individuals who work from home, small businesses and gamers.

With all that speedy yumminess, let’s examine some of the technologies required for delivering multi-gigabit symmetrical services to homes and businesses.

Setting the Stage

When a provider deploys broadband services there is typically a peak rate, above the advertised speeds, that provides the headroom necessary for them to support the speeds and service level agreements (SLAs) associated with the service.

When the total available bandwidth is shared among multiple users, like it is in PON solutions, an unscientific but common practice is for the network to support at least twice the highest advertised rate. Specifically, to support an advertised service of N Gbps, the peak rate must provide for at least 2xN Gbps. Thus, for a 2 Gbps service the peak rate must be at least 4 Gbps to safely support the SLA using common practices. This premise allows the operator to investigate and determine the technology to use in order to support the advertised speeds. Once the technology is chosen, then the engineering work required to build out the solution may begin.

Technology Options

Let’s look at the two fiber to the home solutions that will support a 2 Gbps symmetric service today: Point-to-Point Fiber and 10 Gbps Ethernet Passive Optical Network (10G-EPON).

Point to Point Fiber: Best Performance

Point-to-point topology is a “home-run” active Ethernet fiber implementation that provides dedicated fiber from the home all the way through the access network to the headend. It is analogous to building your own personal highway from home to your office so you can get to work faster. While this solution provides the ultimate future-proof network, in terms of bandwidth, flexibility and network reach, it requires a significant amount of fiber and associated optical transceivers. Running a dedicated fiber to a residential customer premise is both complex and resource intensive due to additional fiber management and ongoing maintenance. However, it delivers the best performance to meet customer needs.

point-to-point-topology
Point-to-Point Topology

10G-EPON: An Efficient 2-Gig Symmetrical Solution

While there are many flavors of Passive Optical Networks (PON), (see: OnePON), 10G-EPON with its symmetric 10 Gbps links, is the only standardized, and commercially available PON technology able to provide at least 4 Gbps peak rate to support a 2 Gbps symmetrical service level agreement. Because of its point-to-multipoint topology and passive implementation, 10G-EPON is a cost effective solution in terms of operations, fiber consolidation, and headend real estate required.

PON-topology
PON Topology

CableLabs has championed PON initiatives through contributions to international standards, hardware and software certification, and interoperability events. CableLabs is facilitating a common approach to provide fiber solutions that will allow for quicker and higher-scale PON deployments.

Conclusion

Both 10G-EPON and point-to-point fiber solutions can provide 2 Gbps symmetrical services, opening up a world of possibilities for cable operators and customers alike. From the realization of all-IP delivered services, more efficient network implementations, improved cloud services, and overall future proofing the network, 2 Gbps symmetrical fiber deployments are a reality today.

Jon Schnoor is a Senior Engineer at CableLabs.

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