January 1, 2008
Coax-Based Home Networks – MoCA Makes Its Bid
Is MoCA ready for prime time?
By Justin J. Junkus
MoCA claims it’s ready for prime time and that prime time is now. MoCA is the acronym for the Multimedia over Coax Alliance and also designates the technology advocated by the group.
At its first Technology Conference and Open House in Austin, TX, the alliance assembled an impressive cast of characters to state the case for home networks as the next opportunity for communications service providers, especially cable operators. Comcast CTO Tony Werner delivered the conference keynote presentation, which focused around a relatively new consumer penchant for creating and accessing large volumes of recorded data. “Sixty percent of all viewing is non-real time, and 85 percent of stored data is created by individuals, not institutions,” he said. He continued by pointing out that the number of digital devices that can be networked in each home is projected to reach 30 by 2010.
According to Werner, the echo-boomers are a digital generation, which wants to participate in networked applications. The range of these applications runs from social networking and online gaming to “wireless intimacy,” a term defined by Motorola in a later talk to describe TV watching integrated with audio conferencing in a virtual TV room for friends or family separated by geography. Within the home, networked applications built around TV-centric service packages are drivers for home network implementations. (See Figure 1.)
But Werner and others were quick to point out that home networking in itself is not a killer application. “Home networking is not a business for Comcast,” said Werner, “but rather a way to build sticky bundles of services that discourage customer churn.”
With such a wide range of applications and devices, cable companies will have to choose what they support when the customer calls for help. Werner’s take is that the cable company has to support the devices it installs, but should leave the responsibility for consumer devices to others.
FIGURE 1: Additional services desired in a bundle, TV-based package
Where MoCA fits
Service providers are beginning to acknowledge that control of connectivity to a home network is a key part of a strategy for creating applications that bind service bundles and make it difficult for subscribers to drop individual services. MoCA is one of several home networking technologies that service providers are evaluating to extend their networks into subscriber homes.
Key criteria in the evaluation process are availability of nodes (devices with MoCA chips, not to be confused with optical nodes in the outside plant) on the network, maximum transmission rate, bit error rate (BER), quality of service (QoS), and management capabilities. MoCA 1.1 provides a 16-node solution and promises that 175 Mbps will always be available to more than 95 percent of the nodes, with a BER target of 1 x 10-9. Its parameterized QoS reserves paths on a flow basis, and management capabilities are provided per the TR-69 standard.
Competing with MoCA for connectivity in the home are wireless solutions, HomePNA, HomePlug and HANA. Several wireless solutions are either available or emerging, including 802.11a,b, and g, and WiMAX. Although these fulfill a “no new wires” objective, they are limited by barriers to wireless transmission within the home caused by structural building materials forming walls and floors. Both HomePNA and HomePlug similarly avoid the need for new wires. HomePNA is, however, limited by conflicts with cable return path spectrum, and HomePlug is struggling with QoS issues and incompatibilities with other powerline-based technologies. HANA, although created as a solution for home entertainment networking, currently specifies IEEE 1394 as its standard for connectivity, and 1394 over coax is still being defined.
What consumers want
MoCA member Intel has done substantial research on the consumer needs that any home networking technology must satisfy. Brenden Traw, Intel CTO, Digital Home Group, points out that information flows for consumers focus around four hubs: around the home, around the PC, around the TV, and untethered “on the go” applications such as mobile handsets, laptops, and personal media players.
“In the technology space,” he said, “consumers are looking for interoperability of content, devices and services. The home network must be simple and robust, yet still provide for tagging, accessing and storage of media.” Radio Shack’s Pete Griffin summed up the consumer perspective, saying, “The consumer is not looking to be educated, but is looking to solve a problem.” Jim Strothmann, director of product strategy and management for Scientific Atlanta, translated these needs into service provider requirements. “The objective is to put the consumer in control (of his information),” he said. “We need to change the perception of a service bundle from least cost to value of services that can be provided across the bundle, which only the bundle provider can offer. Video is a key launchpad.”
How MoCA works
MoCA uses the existing coaxial cable plant in a subscriber’s home as the connecting media for devices on a home network. When devices such as PCs are not directly connected to coax, gateways and bridges provide the link to the coax plant. In addition to the cable itself, the subscriber’s plant also typically contains splitters and sometimes amplifiers. MoCA equipped devices must therefore be able to communicate through high-isolation output ports, as well as in the forward and reverse direction. (See Figure 2.)
This is accomplished using a form of orthogonal frequency division multiplexing (OFDM) that is dynamically tailored to the individual paths in the subscriber’s coax network. “Probe” signals are periodically sent to the MoCA nodes on the plant to determine frequency response at each of the OFDM subcarrier frequencies. The optimal combination of constellation and frequency for each node is determined to achieve a BER of 1 x 10-9, resulting in constellations that can range from no symbols to 256-QAM (quadrature amplitude modulation). Because the electrical characteristics of the plant can change when the subscriber adds or removes devices, probes are sent on a periodic basis, and the OFDM scheme is changed as required.
MoCA operates in a 50 MHz band in the 875-1,525 MHz range, with 12 bands defined. Each system operates on one of the bands. A separate set of usable bands is designated for cable, telephone and satellite company use, to avoid conflict with existing spectrum allocations.
Communication between devices on a MoCA network is under the control of a node designated as the network coordinator (NC). This is usually the node with the highest bit rate performance. A node joins a MoCA network by listening for a beacon signal from the NC. Upon “hearing” the beacon, it sends an admission request to join the network. If no beacon is heard, the new node assumes it is the first and begins transmission of its own beacon. MoCA 1.1 completes the probe and beacon tasks faster than its predecessor MoCA 1.0. This allows an increase in the maximum number of nodes from eight to 16 and provides a throughput increase from 100 to 175 Mbps network throughput for 95 percent of the nodes.
The NC is also responsible for managing transmission timing and the associated QoS. Transmission occurs during repetitive cycles preceded by a MAP. MoCA 1.1 introduced parameterized QoS. In contrast to the prioritized QoS of MoCA 1.0, parameterized QoS is based upon a fully scheduled media access control (MAC) with no collisions. With parameterized QoS, transmissions are allocated on the basis of flows, rather than individual packets. When a device on the network is ready to transmit, the NC reserves a timeslot on a MAP for the required transmission window, which may span several cycles.
Link layer privacy is implemented with password-based 56-bit data encryption standard (DES) encryption. To communicate, nodes on the network must have a matching password, which is entered by the user and stored in the device on the node.
FIGURE 2: MoCA communication paths through a splitter
How Verizon uses MoCA
MoCA is an integral part of Verizon’s broadband strategy. Per Mark Wegleitner, Verizon Communications CTO, there are more than 3 million MoCA devices in FIOS homes today, with 700,000 FIOS video customers using MoCA. “The driving factors behind Verizon’s choice of MoCA as the connecting technology in the home,” he said, “are the ability to reuse existing coax, splitters and connectors and a substantially reduced installation time over other technologies.” Wegleitner also noted that the TR-69 based management capabilities of MoCA make it easy to handle connection and configuration management for subscribers, as well as firmware upgrades.
The “Verizon Managed Home” is an architecture consisting of two MoCA networks in the customer premises. A wide area network (WAN) connects the FIOS optical network terminal (ONT) to a broadband home router (BHT) for network-facing management communications. A separate local area network (LAN) interconnects the BHT with in-home devices such as DVRs and set-top boxes. Future-proofing the home for emerging high throughput applications was critical to Verizon’s choice of MoCA. “In our implementation of the Verizon Managed Home, it was essential to get 100 Mbps throughput into the home, in the hands of the user,” said Wegleitner. Verizon’s roadmap for next-generation MoCA includes a path to 400 Mbps in two years and 1 Gbps in four years.
Few limitations remain
The fact that MoCA is based upon coaxial cable makes it an ideal fit for devices that connect directly to coax, such as set-top boxes and DVRs. However, data storage devices and PCs that will be repositories for photos and other consumer-created multimedia require some type of bridge or gateway to connect them to a MoCA network. The technology showcase that was part of the Austin conference demonstrated that these devices are either available now or soon will be on the market, and when they are included in the network, media can be transparently accessed and sent across device platforms.
The issue of multiple sources for silicon has been resolved with the addition of Broadcom and Conexant Systems to the alliance as MoCA chip providers, in addition to Entropic.
Retail availability of devices with MoCA and how they interface with a service provider’s network is the remaining evolving issue. Devices on a MoCA network must operate in the band assigned by the service provider. At present, automatic frequency agility is not part of MoCA; however, retail devices will operate on multiple bands, using external filters to match them to the network.
At least two cable operators see 2008 as the year for initial deployment of MoCA in cable. Werner noted that MoCA will begin making its mark in cable systems in 2008, with companies “seeding the market” with devices that communicate over MoCA. The most likely application will be multi-room personal video recorder (PVR). Vince Groff, Cox executive director, noted that the July 2007 requirements for CableCard slowed their plans, but trials and deployment of MoCA as part of a multi-DVR solution are part of 2008 projects.
A device certification process has been established by MoCA, through the National Technical Systems laboratory in Culver City, CA. As of November 2007, 15 products have been certified as MoCA compliant.
Justin J. Junkus is president of KnowledgeLink and telephony editor for Communications Technology. Reach him at email@example.com.