Coax has the following advantages: 1) it is already in place where the TVs are located (unlike phone line), 2) it is a shielded network without a lot of conflicting traffic (unlike power line) and, 3) in general can reliably provide enough capacity for the video delivery (unlike wireless today).

Networking The Digital Home

Patrick Donovan | Ucentric Systems

Networking The Digital Home
By Patrick Donovan, Ucentric Systems

Coax has the following advantages: 1) it is already in place where the TVs are located (unlike phone line), 2) it is a shielded network without a lot of conflicting traffic (unlike power line) and, 3) in general can reliably provide enough capacity for the video delivery (unlike wireless today).


Consumers, service providers, and equipment manufacturers are all pursuing a vision of The Digital Home in which consumers have the freedom to enjoy all their digital content - video, audio, images, data - throughout their home. The challenge to simultaneously deliver multiple media types to multiple devices in a simple, secure, user-friendly approach is a significant one. This article will focus on the varying approaches being taken today by current cable set top box vendors to deliver The Digital Home.

A number of recent trends around digital media are culminating in what is being called The Digital Home. A primary driver is the pace of DVR shipments and the overwhelming desire of a DVR customer to have DVR capabilities on every TV in their home . Cable set top box manufacturers Scientific Atlanta, Motorola, and Digeo have all introduced products designed to deliver DVR service to multiple TVs, although each have a different connectivity approach. These different approaches will be examined in this article.

In addition to DVR, the other building blocks of The Digital Home include digital music, digital photos, digital telephony, broadband data (home data networking), and other IP based content/applications. The usage of each of these other types of content is rapidly increasing. Consumers now have a variety of devices, including TVs, set top boxes, PCs, stereos, MP-3 players, digital cameras, etc., that can be either places to store content, consume content, or both. Making all of this varied content accessible to all of the various devices in a seamless, interconnected fashion is the central goal of The Digital Home.

Using coax as the backbone

The ideal approach to networking The Digital Home is to require no new wires. Options include using the existing phone lines, power lines, coaxial cable, or a wireless approach. The multiple TV DVR products introduced by Scientific Atlanta, Motorola, and Digeo all use coaxial cable as the primary physical layer to inter-connect the TVs in the home. Coax has the following advantages: 1) it is already in place where the TVs are located (unlike phone line), 2) it is a shielded network without a lot of conflicting traffic (unlike power line) and, 3) in general can reliably provide enough capacity for the video delivery (unlike wireless today).

While all of these set-top products use coax, each is using a different protocol/approach on the coax - Digeo's BMC 9022 built by Motorola is using analog-based distribution, Scientific Atlanta's 8300 Multi-Room DVR is using QAM-based, and the Motorola 6412 Advanced Home Media Architecture is using IP-based networking (the Multimedia over Coax Alliance (MoCA) standard). Let's examine each approach.

Analog distribution via coax cable

Analog distribution provides few benefits over currently available digital networking options. While multi-TV DVR using analog distribution may be cheaper in some configurations, the advanced set top box (ASTB) requires significant resources to support each stream. All user interface graphical overlay information needs to be blended in the ASTB, adding significantly to the memory requirements of the box. The current silicon for this analog distribution only powers one additional TV, so an additional chip is required for each TV to be connected.

Figure 1: Analog Distribution

Another concern with the analog solution is that it lacks privacy, and makes parental control a challenge. Each stream from the ASTB is sent in the clear over the in-home coax. Anyone in the house can easily see what other members of the family are watching. For example, if the ASTB is re-modulating on channel 8, any TV in the home that is tuned to channel 8 will see the content.

Also, signal integrity issues of analog distribution mean that digital cable customers will notice degradation in the quality on their secondary televisions. Perhaps more significant, analog distribution will not support high definition, digital music, data networking or other IP based services. Analog distribution is not really networking, it is simply connecting a secondary TV to an advanced set top box. For the reasons above, the full vision of The Digital Home cannot be achieved using analog-based distribution.

QAM modulation

The desire by cable MSO's to reuse legacy set top boxes as thin clients has led to an in-home networking approach which mimics the out-of-home signaling used from the cable headend to the set top. Technically, this is MPEG encapsulation with QAM modulation (downstream) and QPSK modulation (upstream) within the home. The advantage of this technique is that existing low-end set-top boxes can be reconfigured to serve as thin-client devices utilizing their in-band and out-of-band network interfaces for communication with an advanced set-top box. This is the approach used by Scientific Atlanta's Explorer 8300MR DVR set top box to connect to up to three Explorer 2000 (or higher) set top boxes on other TVs in the home.

Certain drawbacks of adopting this legacy networking approach include (a) a limited feature set on the client set tops, b) the cost of new equipment, and (c) the asymmetric communications channel. While the cost of this approach is partially mitigated by the reusability of legacy boxes, the cost of new equipment is driven up by the addition of non-commodity QAM modulation silicon.

These QAM modulation chips allow the advanced set top box to connect to the other low-end set tops, but recreate the inherently asymmetric communications channel supported by the legacy equipment. The lack of a high-speed back channel in the legacy equipment eliminates the possibility of pooling networked resources such as tuners. One result is that the thin-client, low-end set tops cannot do some of the fundamental DVR functions such as pausing live TV. Since the tuner that is local to the low-end set top cannot direct its program stream back to the hard drive in the advanced set top box, the user in front of the low-end set top box cannot pause live TV or use any other of the highly used DVR control functions such as rewind, fast forward, instant-replay while watching live TV.

Figure 2: QAM Modulation

The DVR/EPG application itself is not networked either, in the sense that the client, low-end set tops cannot schedule programs to record. Therefore, the user can only schedule programs using the TV connected directly to the advanced set top box. Customers are likely to be confused about being able to do some functions on the main TV, and not on the other TVs in the home. The result will be increased customer support calls.

Finally, the QAM modulation approach is not suitable for IP traffic and hence cannot support all the IP-based services and applications like digital music and photos that make up an important part of The Digital Home.

IP-based networking over coax

IP-based networking over coax has gained significant traction in the past year. IP-based networking for video is being used today outside of the home in Gigabit Ethernet implementations for VOD distribution systems. In the home, IP-based networking offers increased performance and cost savings that results from the flexibility and extensibility of IP.

From a cost standpoint, IP-based networking can utilize the same chip technologies found in common data-networking products and thus leverages massive consumer and commercial volumes to provide a low cost solution. Several networking options are available today that deliver IP-based networking over coax, including HPNA-over-coax, 802.11g-over-coax, and the MoCA approach. The Multimedia over Coax Alliance (MoCA) was formed in January of 2004 "to develop and promote specifications for the transport of digital entertainment and information content over in-home coaxial cable." MoCA is working on a technology that promises enough bandwidth for multiple high definition (HD) streams through the home along with music, data and other simultaneous streams. Motorola has chosen MoCA to network its Home Media Architecture offering.

Performance advantages derive from both the multi-use nature of IP and the rapid evolution of IP networking technologies. The use of IP means that the video can be sent in its digital form, including in high definition, throughout the home. There is no loss in video quality on the secondary TVs. This all-digital approach is obviously synergistic with the move to all-digital distribution being mandated by the FCC. The same IP network used to distribute SD and HD quality video signals can also be used to provide a very high bit rate home networking solution for Internet access.

Since all new media formats are digital, the IP-based network can support distribution of digital music files in diverse formats, digital photos, and even personal camcorder files. That means consumers can download their home movies on to the advanced set top box (server) then watch them anytime they want, anywhere in the home. It also means that emerging premium IP-based audio, photo, and video services can be made available throughout the home.

Figure 3: IP-based networking

Because of the bi-directional nature of the IP-networking approach, the resources across the networked set top boxes can all be pooled together. For example, the tuner in a basic set top box can direct its program stream across the coax network to the hard drive in a DVR set top box, then back to the TV connected to the basic set top box. The result is that the user can control the live TV stream, including pause, rewind, instant replay, etc. on the 'client' TVs just as they can on the primary TV. This means that a home with one dual-tuner DVR set top box, and two networked basic set tops have a total of four tuners that are pooled and usable throughout the home. This is then a true networked environment, not the point-to-point connected methods used in the analog and QAM approaches.

Also, all the same features are available on all TVs, so users can schedule a recording from anywhere. This consistency of experience and capabilities throughout the home will drive better customer satisfaction and lower support calls than any of the non-IP based methods.

In addition to the significant bandwidth, digital quality video and audio, and extension to IP based media, this approach offers the flexibility to use the coax as the network backbone in the home, then attach additional access points to the coax nodes, or the clients, for the wired or wireless networking to PCs and other IP based devices throughout the home. This hybrid wired/wireless approach is the ideal method to network the various devices in the home and securely deliver digital quality video and audio throughout the home.

The table below summarizes the relative strengths and weaknesses of the various approaches being used today to deliver The Digital Home.


Networking approach over coax

Features & Applications




No new wires installation

Watch recorded content on all connected TVs

Full featured DVR on all connected TVs


Low cost silicon available


Broadcast quality digital video delivery throughout home



Maintain digital encryption throughout the home


Digital pay TV services available throughout the home (HD, VOD, iTV)


Extensible - pool resources (hard drives, tuners) across home



25 - >100 Mbps bi-directional throughput



Multiple High Definition streaming capability



Networked digital (IP-based) music capability



Networked digital photo capability



Broadband Internet access (wired and/or wireless)



Supports other IP-based services



Patrick Donovan, Vice President of Product Management

Patrick Donovan has more than a decade of business development and implementation experience with software companies. Donovan is responsible for establishing and managing relationships with Ucentric's network operator, set-top and consumer electronics manufacturer, and technology partners.

Prior to Ucentric, Donovan was director of operations for CareTools, Inc., an enterprise software provider to the healthcare industry. He sold and led the implementation of the company's software suite, which included electronic medical record, billing, scheduling, and decision support modules. Previously, Donovan was a management consultant for Grant & Partners, focused on helping companies segment and optimize their customer base. Prior to that, Donovan was a senior associate at Symmetrix, Inc., now part of Next Era Enterprises, where he consulted to and implemented software for companies in the healthcare, manufacturing, and insurance industries.

Donovan earned a Bachelor's of Science degree in Management Science from the Massachusetts Institute of Technology and a Master's of Business Administration degree with Honors from Harvard Business School.

Comments (0)

This post does not have any comments. Be the first to leave a comment below.

Post A Comment

You must be logged in before you can post a comment. Login now.

Featured Product

Light sockets; Not just for lights anymore

Light sockets; Not just for lights anymore

Smart Bulbs are out there and they can do far more then just provide light. Speakers, projectors, wi-fi extenders and more. The standard light socket that is wired up and ready to go in nearly every home in North America is now providing an easy and affordable option for home owners and renters alike to enter into the world of the "Smart Home". Here is a look at some of the Smart Bulbs and Smart Lighting options out there, and this list is just the beginning. In this ongoing article we hope to continue to add to and grow this list, so stay tuned!