Articles and whitepapers

Introducing MoCA - the Multimedia over Coax Alliance (2/10/2007)

By Anton Monk, Entropic Communications

Consumer adoption of digital media is in full swing. Whether it be photos, music or video, consumers have embraced the fact that their entertainment can be stored on personal computers, digital video recorders, set-top boxes or streamed directly from online service providers. However, now that consumers have access to all of this digital entertainment, they are no longer content to confine their viewing experience to a single television in the home. A consumer wants to be able to watch their favourite video program on any television - in the family room, the bedroom or the den.

The challenge is providing a home network that has the bandwidth to support multiple standard-definition and high-definition programmes in a highly-reliable manner so that the viewer has a 'glitch-free' experience. In addition, both consumers and installers do not want the extra burden of having to install new wiring. Wireless, phoneline and powerline solutions offer the promise of TV in any room, but in reality, the throughput and coverage are not adequate to address multiple video streams and ensure a satisfactory experience. In contrast, coaxial cable provides an ideal medium for a home network due to its wide bandwidth, co-location to televisions and shielded nature that makes it highly robust against interference.

The Multimedia over Coax Alliance

The Multimedia over Coax Alliance (MoCA) is an open, industry-driven initiative, that promotes distribution of digital video and entertainment through coaxial cables in the home. Promoter members include Cisco, Comcast, Cox, EchoStar, Entropic, Matsushita (Panasonic), Motorola, RadioShack, Toshiba and Verizon. The goal of MoCA is to create specifications and develop a certification process for MoCA-based products. Having achieved these goals in March 2006 with the ratification of the MoCA 1.0 specification, MoCA now includes over 50 alliance members representing a wide diversity of industry interests including cable, DBS and telco system operators; ODMs and OEMs; silicon and component vendors; and mass-market retailers.

MoCA technology was designed from the ground up, to address the key requirements for networking digital video within the home:

* High throughput - 270Mb/s PHY (PHysical laYer) data rate.
* Low packet error rate - better than 1e-5.
* High outlet coverage: 97% of all outlets achieve greater than 100Mb/s with no modifications to the existing home coax network.
* Quality-of-service (QoS).
* Security and Privacy.
* Ease of use.

How MoCA technology works

From the outset, MoCA recognised that a homeowner's coax may already be used for other television or data modem services. Therefore, MoCA was designed to coexist with these services and tap into the unused bandwidth to provide a full mesh, peer-to-peer network. MoCA enables multiple and simultaneous SD and HD programmes to be sent from any coax outlet to any other or multiple coax outlets in the home. For example, a child in the bedroom could be watching an SD television show, while mother is watching an HD movie in a different room and father is watching an HD sports game in the family room. All of these programmes can originate from a single source like a set-top box, or the programmes could exist on various DVRs (digital video recorders), PCs or set-top boxes scattered around the home. All that is required to support distribution scenarios like this is a MoCA-enabled coax network.

Typical MoCA residential setup using coax to network broadband multimedia, digital broadcast satellite, DVR, online gaming, set top boxes and wireless devices.

At the network's physical layer, MoCA uses forward error correction algorithms and advanced modulation techniques adapted to work over coax. The technology is based on OFDM (orthogonal frequency division multiplexing), but MoCA dynamically adjusts the amount of symbol information carried by each OFDM subcarrier in order to maximise data throughput on a per channel basis. MoCA calls this ACMT (adaptive constellation multi-tone) modulation. If there are dips or nulls in the channel's frequency response, each ACMT subcarrier is loaded with the maximum QAM (quadrature amplitude modulation) constellation that can be reliably transmitted through the channel. The result is a transmission adapted to the channel that maximises data throughput as much as possible while achieving low packet error rates.

Recognising that video traffic requires highly-reliable, low-latency transfers without retries, MoCA uses a fully-coordinated collision-free MAC (media access control). The MAC uses TDD (time division duplexing) media access to assign transmission time slots to each node. Using this method, network latency is deterministic and is controlled by a master node called the network coordinator. Also, since the PHY packet error rate is so good and the MAC is collision-free, there is no need to waste network bandwidth and incur increased latency using data retransmission schemes required by so many other network standards.

MoCA chipset by Entropic Communications for OEMs.

Since MoCA only defines the PHY and MAC network layers, it can be used in a variety of different products such as set-top boxes, routers, PCs, digital media adaptors and network bridges. Setup of a MoCA network involves entering a common password for each node, but after that, nodes will automatically scan the coax for other nodes and form the network on their own. MoCA maintenance and diagnostic data gathering can be supported by the DSL Forum's TR-069 protocol for CPE management functions.

Conclusion

Using MoCA, consumers can liberate all their digital media and enjoy their entertainment in any room in the house. Photos, music, games, Internet access and SD/HD video scattered on devices around the home can be made accessible in rooms wherever there is a coax outlet. MoCA is already being integrated into greater numbers of set-top boxes, network bridges and routers and will eventually make its way into consumer electronic devices.

From the beginning, MoCA was the only home networking standard developed with multimedia distribution as its primary goal. As such, it is the only network technology that can deliver on the promise of throughput and coverage with packet error rates low enough to support distribution of multiple streams of SD/HD video. This is backed by the fact that over 5 million MoCA nodes are already being used by system operators in U.S. homes today. As more digital content and HD displays proliferate into homes around the world, MoCA is the natural choice when it comes to addressing the consumer's desire to have their digital entertainment simultaneously available on multiple devices in multiple rooms.

Anton Monk PhD, is Vice President of Communications Technology for Entropic Communications, Inc, and Chief Technology Officer for the Multimedia over Coax Alliance. The author would also like to acknowledge the contributions made to this article by Jon Iwanaga, Technical Marketing Manager for Entropic Communications, Inc.

www.entropic.com
www.mocalliance.org