Articles and whitepapers

Simplifying HD Home Networks (5/11/2007)

By John Santhoff, Pulse~LINK

Networks have become ubiquitous. They have completely altered how and where we use 'traditional' devices like phones and computers. 3G mobile phone networks have turned our phones into mobile PDAs and TVs, while our home phones are connecting to the Internet for VoIP (Voice over IP), and our PCs have become Skype phones. YouTube, blogs, instant messaging, Facebook - everything seems to revolve around connectivity and networks.

Meanwhile, WiFi introduced home networks into our lexicon. It has untethered our laptops and PDAs and many new mobile phones come with WiFi built in. In the U.S., you can even order a Big Mac with a side order of WiFi. So, with everything else moving across networks, it is only natural that we should expect our entertainment devices to be connected - particularly our high-definition devices. If you could share your HD sources among all your TVs instead of having to buy or lease one for each room, you might actually buy a second and third HDTV. Yet, despite years of promises, the TV is not typically connected to the home network. Why? To answer that question, we first need to examine the differences between data and HD networks and understand consumer expectations.

When networks move data files (documents, browser screens, etc.), the time it takes to move the data from point A to point B is measured in 'human' time. Whether it takes ten milliseconds or half a second to get there is insignificant. If some of the data is lost or damaged, it gets resent. Entertainment on the other hand is 'real-time'. Whether the data is lost, damaged, or late, the picture suffers because the next frame can't wait.

Keep it simple - entertainment and consumer expectations

As important as picture quality is, and picture quality is why we buy HDTVs, simplicity and reliability are even more important. Anyone with a computer knows that PCs crash and require maintenance. Adding a network just adds to the problem by opening the door to viruses and hackers. For the most part, we have come to accept this because of the advantages gained through our networked PC. But when it comes to our TVs, we expect them to just work. Virus, crash, hack, reboot, drivers, these are words no one wants to associate with TV. Unfortunately, many entertainment systems have already become too complex. Many of us long for the 'good old days' when we just plugged it in, attached one wire and watched TV. With a well-designed entertainment network, those days will return. Plug the network into the DVD player and the TV and press 'play', even if the TV and the DVD player are in separate rooms.

Let's get technical

While the goal is to make it simple and reliable, to understand how to do it we need to get a little technical. First, we need to realise that devices connect at multiple levels.

The lowest level of connection is the Physical Layer (PHY), the part that carries the actual digital bits. The PHY determines the bandwidth or how many bits per second (bps) the network can provide. HD video requires anywhere from 8-10Mbps (MPEG4) to 20Mbps (MPEG2), to as high as 38Mbps for cable, continuously! Special features such as 'trick play' (fast forward/rewind) can require up to 80Mbps. The average may be lower, but a network must guarantee the peak, not the average. A single networked personal video recorder (PVR or TIVO) which can record two channels and play back two more will use four 'streams' of data, as both record and playback are done simultaneously to the hard drive. That means it requires anywhere from 40 to over 200Mbps depending on the source and use case.

The next level above the PHY is the Media Access Control or MAC layer. There are two fundamental types of MACs in networking, asynchronous MACs such as Ethernet, WiFi and the Internet, and isochronous MACs such as FireWire (IEEE 1394) and IEEE 802.15.3b. Isochronous networks operate like a railroad system. Everything runs on a schedule that is controlled using a common system-wide clock. When you hit the play button, the network reserves whatever bandwidth is necessary to guarantee on-time delivery, just as space is reserved on a train. Asynchronous networks are similar to highways. The time of arrival is dependant on the amount of traffic, accidents (data collisions) and other factors. TVs need guaranteed delivery. With an asynchronous network, the only way to guarantee delivery is to have lots of spare bandwidth. Even then, delivery is not truly 'guaranteed,' it is just more likely that it will be delivered on time.

Lots of choices, few solutions

The ideal network will not require any new wires, so a lot of work has been put into powerline (HomePlug) and WiFi wireless networks. Unfortunately, neither powerline nor wireless can provide the hundreds of Mbps of throughput needed for whole-home HD video distribution. They can reliably handle one or two streams at best. Phone wiring is another contender but here too, it is limited in speed and in reality the phone jacks are typically in the wrong locations within the home to enable networking of the devices we really want to network.

This leaves CAT5 unshielded twisted pair (UTP) and coax. Certainly CAT5 structured wire running gigabit Ethernet (1000Mbps of bandwidth) is a contender from a throughput perspective. It is asynchronous, but it has lots of bandwidth. Solutions have also been developed for FireWire over CAT5 wire at up to 400Mbps. Since FireWire is isochronous, it provides approximately the same sustained throughput as gigabit Ethernet.

Coax cable can be found in most homes throughout North America and in many parts of Asia, and in European homes receiving terrestrial, satellite or cable TV. It has several advantages over CAT5 UTP in that it already connects to consumer entertainment systems so there is no 'education' needed, more homes are wired with it than CAT5, and it is more rugged. A kink in a CAT5 cable can reduce its ability to carry high speed data. That said, either CAT5 or coax can provide the needed throughput for multiple streams of HD video.

The next higher level in the networking 'stack' is the networking protocols. Most of today's entertainment is delivered by cable, satellite, or terrestrial broadcast networks. While these are networks in a sense, they do not use 'traditional' networking protocols and therefore cannot be networked directly in the home. The other main protocol used to deliver content to the home is IP (Internet Protocol) such as IPTV and the Internet. IP defines a network layer which lies above the PHY and MAC and is therefore independent from the MAC and PHY layers. Most modern networks use IP at the network layer and, not surprisingly, both Ethernet and FireWire support IP as well.

That brings us to the upper layers of the network, the ones that the customer actually 'sees' and that allow devices to interoperate. Even if devices use the same PHY, MAC, and IP layers, they may not interoperate unless the rest of the network 'stack' is the same. These higher layers define how devices will 'discover' what other devices do, the commands they can support (play, record, mute, etc), how the content is encoded, and so on. There are two leading organisations working on providing a complete network solution for entertainment: the High Definition Audio-Video Network Alliance (HANA), which is focused on HD networking using 1394 connectivity, and the Digital Living Network Alliance (DLNA), which is focused on interoperable networks for PC, consumer electronics, and mobile devices with Ethernet, WiFi, or Bluetooth connectivity.

Tying it all together

An example of a system that supports both DLNA and HANA is the Pulse~LINK CWave Whole-Home Interactive HD solution. This supports a PHY data rate of 1.35Gbps, which for home networks, yields greater than 400Mbps useable application layer throughput over hundreds of feet of coax cabling - even when multiple splitters are used. CWave uses an Ultra Wideband (UWB) radio frequency signal operating at 3-5GH, so it is 'out-of-band' and completely co-existent with legacy signals on the coax wire (cable/satellite/DOCSIS modems which all operate below these frequencies).

The Pulse~LINK CWave whole-home coverage hybrid wireless/coax network.

The same chipset that enables multiple simultaneous HD video streams to be distributed over the existing coax throughout the home also provides wireless connectivity in each room. CWave is both isochronous and asynchronous, supporting FireWire, Ethernet and High-Definition Multimedia Interface (HDMI) simultaneously over the same network. HDMI is becoming the preferred direct (non-networked) link between DTVs and digital sources such as DVD players, satellite receivers, and cable Set-Top Boxes (STBs) and is likely to be included in most IPTV gateways. In addition to providing a whole-home network for room-to-room distribution of digital content, a short-range wireless HDMI entertainment network is necessary to eliminate the 'rat's nest' of connector wires behind entertainment systems and allow clean installation of wall-mounted flat-panel displays.

The Pulse~LINK CWave PL3130 chipset block diagram.

Pulse~LINK has conducted numerous demonstrations showcasing HANA networked devices and DLNA certified devices working simultaneously on the same coax cable, and its ability to simultaneously deliver 1394 and Ethernet over a single coaxial cable enables products based on either network to coexist within the same home.

HD networks: the future is now

Today, most video is moved around the home as an analogue signal. There have been no networking solutions fast enough and with the necessary QoS (Quality of Service) to simply, reliably, and cost-effectively move digital HD content around the home. This is changing. With HANA and the DLNA creating the guidelines and with products such as CWave moving FireWire, Ethernet and HDMI over existing wires and wirelessly, these problems are being solved. Our entertainment systems will become connected, bringing back the 'good old days' of one wire, one remote simplicity.

John Santhoff is the Founder of Pulse~LINK and its Chief Technology Officer. Pulse~LINK's CWave UWB technology enables high data rate whole-home networking of HD content from a hybrid wired/wireless chipset.

www.pulselink.net