Leveraging MoCA for In-home Networking
SOURCE: Converge! Network Digest
by Anton Monk, Chief Technology Officer
A home digital entertainment network consists of multiple streams of standard and high definition content distributed anywhere, anytime throughout the home. There are numerous technologies and mediums vying to become the standard in the digital home but not all are created equal. Many of these mediums are voice and data centric. Still, despite the rise of 802.11n broadband wireless links in 2007, Wi-Fi will not be the ultimate solution for networking digital entertainment in the home. The most obvious medium for delivery of video to and around the home is still the one that has been in use for generations -- coax.
Unlike data delivery, occasional glitching, blocking or "buffering please wait" will not be tolerated for entertainment networks. Park’s Associates’ recent report, "Trends in Consumer Technology: Defining and Sizing the Market", notes the challenge will be not in the number of players providing delivery, software development or platform design – but in the way these companies and organizations determine the technology standards and delivery mediums that make the digital lifestyle a reality.
So, Why Coax?
Coax offers benefits not found in other digital entertainment home networking mediums, including it’s inherent shielded nature, which eliminates security concerns, and it is already in use within 90% of U.S. homes as the preferred delivery medium of most service providers.
Coax has massive amounts of potential bandwidth available in currently used portions of the spectrum. The cable or terrestrial television spectrum occupies frequencies on the coaxial cable up to about 850 MHz. Above this band are Gbps of bandwidth available for current and future networking use in the home. Satellite signals typically occupy frequencies above 950 MHz so any coax networking technology must be able to use spectrum below this. For those homes that receive both cable / terrestrial and satellite services, the networking technology must be flexible enough to fit between the two bands.
The Multimedia over Coax Alliance (MoCA) solution has been designed to tap into this tremendous bandwidth and to fully interoperate with cable, terrestrial, and satellite signals. A single MoCA channel occupies 50 MHz of bandwidth, allowing physical layer throughputs greater than 250 Mbps.
Data Rate Requirements
A home network designed for the digital lifestyle must also support peak data rate per stream as well as those streams that peak simultaneously. The vast majority of broadcast content in the USA today is MPEG2. Measurements of streams from the top four US service providers show that SDTV MPEG2 broadcasts are variable bit rate with average data rates between 2 and 3 Mbps while peak rates are around 9 Mbps. VOD SDTV streams tend to be a constant bit rate between 4 and 5 Mbps.
HDTV MPEG2 streams can also carry the requirements of content providers for a minimum of approximately 12 Mbps allocation. Fast forward, reverse and other trick modes increase the peak data rate by a factor of 3 or more if continuous streaming video is desired during the trick mode.
Service providers will still need to make terrestrial or network ATSC content available to their subscribers. So even if an advanced codec brings the service provider’s data rate down for HDTV, the subscriber may sometimes home network ATSC. Service providers must allocate the home networking data rate for multiple ATSC streams at 19 Mbps regardless of their own HDTV data rates.
The bottom line is that virtually all operators and service providers target 100Mbps of net throughput as a requirement for the multimedia networked home.
Key requirements for a digital lifestyle entertainment home networking environment are reliability and ubiquity. Both these elements are required in order to provide a comprehensive digital entertainment home networking environment. For the operator and service providers a viable home networking solution is one that achieves greater than 100Mbps of net throughput, without any changes to the home environment, in greater than 95% of all homes, and with simple remediation in the remaining 5%.
Coaxial cable has been used by the cable industry to deliver video and other services for many years. One would think that all technical challenges would have been well understood for some time. However, in the past, the in-home coax has never been used for networking from room to room. This type of coax network poses unique challenges due to the high dynamic range requirements and the potential for large signal echoes. These echoes are a byproduct of the signal having to pass ‘backwards’ through a splitter while at the same time traveling in the standard direct path and bouncing off a separate device further downstream.
Another challenge is the need to maintain very low latency for both video and gaming. In most data networks, link layer retransmissions are used to achieve the required packet error rates. However, for the above-mentioned applications, there is no time for the network to retransmit packets – the packets must get through the first time. The dispersive channel environment referred to above makes this a difficult problem to solve.
The result of these challenges is the requirement for an extremely robust modulation scheme that can handle large echoes without retransmissions. MoCA has been designed to solve these challenges through the use of an advanced modulation scheme based on OFDM.
Reliability from Appliance and Neighbor Interference Requirements
The digital entertainment home network should likewise not degrade due to other networking devices or typical electronic devices and appliances such as cordless phones, wireless laptops, wireless hot spots, vacuum cleaners, power drills, hair dryers or microwave ovens.
Quality of Service Requirements
When the aggregate content’s data rate exceeds, on a peak or average basis, the digital entertainment home networking data rate, then some packets must be delayed and/or dropped. Prioritization must be used to delay or drop lower priority traffic (typically data traffic). Video packets can not generally be delayed or dropped and must have their data rate fully supported otherwise the video will be degraded.
In practical usage, where data rate is taken up by high speed videos, the important elements to ensure a quality
digital lifestyle experience are:
• high aggregate data rate of >100 Mbps net throughput
• low PER of <1e-5
• low latency (< 10 msec)
• guaranteed packet delivery
No new wires or changes of any sort to the in-home infrastructure should be the > 95% rule. A PC should not be required for self-installation of a digital entertainment home network. Recall that the target users of a digital entertainment home networking system are TV viewers, not necessarily PC users.
When deciding on a particular multimedia home networking technology, many factors need to be considered. MoCA suggests the following minimum checklist prior to settling and adopting any one particular medium or standard.
1. Independent field-tests. MoCA has conducted independently verified field tests of 250 homes around the U.S. validating net throughputs of more than 110 Mbps in 97 percent of all outlets—a minimal service provider requirement. One hundred percent coverage was achieved with the addition of an inexpensive filter. Results are available to all who ask.
2. Certification process for interoperability. One of the primary functions of any technology alliance and standard consortium is to provide regular and ongoing certification processes guaranteeing conformance with the standard and interoperability. To date, MoCA has conducted three such certification waves and has certified 17 products.
3. Performance and other technology claims should be forthright and proven. While MoCA technology is capable of 270Mbps, net throughput numbers are quoted often. PHY rates and theoretical bit rates indicate scalability and robustness, but net throughput is an better indication of the true performance of a particular technology standard. Hence, MoCA quotes reality rather than wishful thinking.
4. Broad membership support. The MoCA board of directors consists of a broad cross-section of some of the largest cable, satellite and telco service providers as well as the largest settop box and networking vendors in the U.S and some of the largest consumer electronics and retail entities. In addition, MoCA members include all the major semiconductor companies and a large ecosystem of vendors necessary to make the multimedia connected home a reality.
5. Reasonable and non discriminatory (RAND) licensing. Such an environment guarantees access to the specification for development of products without concerns of legal entanglement in the future. It also helps proliferate the standard by making it easier for vendors to adopt and deploy without burdensome licensing fees.
Any alliance or standard consortium member, not wholly compliant with an alliance’s RAND, can be subject to unreasonable fee collection and even lawsuits. The most significant action a company can do before joining an alliance is to review the compliance requirements and determine applicability to the company’s current and future products. Conducive RAND environments develop ecosystems in which many vendors can develop products and where multiple service providers can deploy with confidence that there are numerous alternative vendors all in compliance with the standard.
Asking the questions posed below will provide a basis for determining longevity of an alliance’s RAND ecosystem:
Will the RAND hold up under multiple deliver options or transport mediums?
What happens when a company or member applies the alliance’s standard to other mediums?
Who holds the underlying technology IP for the alliance’s technology standard and what is the RAND for that IP?
6. Proven deployment. MoCA has been deployed in about 200,000 homes across the United States. Over one million MoCA nodes are now in successful use. This is the ultimate proof of a new technology’s capabilities, performance, and robustness.
Dancing with the one who brought you
The digital entertainment portion of triple play is the Holy Grail of home networking. By ensuring that the requirements above are met and exceeded, operators, service providers and consumer electronics companies can confidently offer digital lifestyle participants entry to the last frontier – controlling and managing the home entertainment experience. Consumers, entertainment companies, equipment and service providers need to remember who brought you this far – coax. It’s proven, it can be deployed ubiquitously and has unmatched reliability. So make the right choice and continue the dance with the one who brought you to the party.