A Little MoCA with your Home Network?

A major challenge faced by service providers is finding a viable strategy for ferrying signals around homes crammed with increasingly sophisticated, bandwidth-hungry networked electronic equipment.

The sector is in its infancy. Because the need for sophisticated home networking protocols is relatively recent, it promises to be a hot topic. There are several groups working on this issue, including HomePNA, HomePlug and the Multimedia over Coax Alliance, which released a new version of its spec last week. Three Changes in MoCA 1.1 The new MoCA spec features three upgrades, said Anton Monk, MoCA board member and VP communications technology and co-founder of chipset vendor Entropic: An increase in bandwidth, a doubling of the number of outlets in the home that can be supported, and a way to prioritize application delivery to favor the service providers’ offerings.

The usable data rate has jumped from 100 Mbps to 175 Mbps. It should be noted, Monk said, that both numbers represent bandwidth that actually is available to devices and applications, not theoretical figures.

More importantly, Monk said, is that testing on the older 1.0 standard indicated that that data rate was available at 97 percent of the outlets in the home. The newer spec maintains that level of delivery while increasing the bandwidth by tweaking the approach to the media access control (MAC) layer. The MAC does this through packet aggregation, which enables groups with similar packets – those carrying the same content and headed to the same destination – to be grouped together. They can be pushed through with less overhead than the previous version, Monk said. This increases the potential payload size.

MoCA 1.1 doubles the number of delivery points – Monk refers to them as outlets – that can be supported to 16. The biggest challenge in supporting more nodes is navigating the complex echo problems that characterize in-home coaxial connections. This, Monk said, is done in the MoCA spec by using pre-equalization to smooth out the differences in the echo profiles between outlets. The use of bit-loaded orthogonal frequency division multiplexing (OFDM) enables this to be done in a fine-grained manner. MoCA 1.1 increases the speed at which link characterizations can be done to the extent that 16 outlets can be supported.

Last – but certainly not least – is an expanded prioritization scheme. In fact, Monk said, the most significant change from MoCA 1.0 to 1.1 is parameterized quality of service (QoS).

In the emerging world, content will enter the home from a variety of sources. Service providers, Monk said, are worried that such high contention will interfere with delivery of their applications.

Existing in-home QoS approaches prioritize traffic. This is not enough to assuage service providers. Parameterized QoS takes the important step of guaranteeing capacity to applications designated by the service provider. The bandwidth is not pinned up, however: If the service provider’s prioritized application is not using its allotment at a given point in time, the bandwidth is available to other applications. – Carl Weinschenk