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IP-based A/V Networks

By Jeremy Aston, Reality Logic

The opportunity to deploy integrated smart home technologies has grown massively over recent years. Technology that was once associated with only the most expensive, high-end properties can now be found in more modest ones. Nowhere is this more apparent than in multi-room entertainment.

Home improvement shows, lifestyle magazines and the Internet all now promote smart home products aimed at the mass consumer market. In the main, these solutions are based on traditional audio/video (A/V) distribution techniques, where a number of sources are connected to a switch that distributes the analogue signal and is controlled using signal relays (e.g. keypads) in each zone.

Although there are some very neat solutions on the market, these approaches do bring a certain level of complexity, since it is not always possible to determine the appropriate wiring to use until a product has been chosen. Which cables are needed to send the audio and video signals to each zone? Are speakers active or passive, and what will be the associated power supply requirements? Where will amplification occur? A product based on the A-BUS approach, which uses local amplification, will require different wiring to one based on centralised amplification, star-wired straight to speakers.

We are all looking for ways to simplify wiring requirements, and are also well aware that computer networks are now much more common in the home. Structured cabling in a property means that there are numerous CAT5e (or, increasingly, CAT6) un-twisted pair (UTP) cables going to each room. There is massive interest therefore in making use of this cabling to distribute A/V around the house, especially for source content such as MP3, FLAC, MPEG and so on, i.e. audio and video in digital form - something that computers understand.

Many solutions already make use of computer network cabling for multiroom solutions, whereby low-voltage signals carrying control, power and AV are distributed from switching hardware to controllers, amplifiers and speakers. In such solutions, the network cabling is simply being used to transport analogue signals and replace traditional power, speaker or coax cables - sometimes using devices like baluns. More often than not, cabling for these solutions is actually separate to any computer network cabling, but what we are interested in is the use of the network cabling to carry digital signals in the same fashion that computers talk to each other on the network. What we are interested in is IP-based A/V networks.

What is an IP network?

When we talk about IP-based networking, we are referring to a method of communication between hosts (e.g. computers). More commonly, we talk about TCP/IP - the communication method that is mostly used on modern networks. Digital data is organised in chunks or 'packets' of data and shunted around the network. The Internet Protocol (IP) part of the acronym refers to the protocol that defines the structure of the data packets, and the Transmission Control Protocol (TCP) part of the acronym refers to the protocol that organises the data packets and ensures that they all arrive reliably.

A simple analogy would be a rail network with a twist. On a normal railway, a train is made up of a number of carriages that stay together throughout the journey. But with our TCP/IP network, the train splits up during the journey and different carriages use different routes. IP defines what the carriages are like, and TCP ensures that the carriages obey the rules of the railway, and are assembled, in the correct order, back into trains as they approach their destination.

The advantages of using IP

The advantage of using IP, is that many different signals can use the same network at the same time. We do not need separate cables for carrying CD audio, Internet video and data to the kitchen for example - they can use the same cable - just like carriages from different trains can use the same track. This means that cabling can be simplified, and a new A/V source, just like a new train, can easily be added to the existing network. Also, being digital, the signal quality is not affected by the length of the cable run.

What makes up an IP-based A/V network?

To distribute A/V in this way, the source material must first be in a digital form. It must then be sent from a source to a destination over the network, and then be converted to the analogue audio or video that we can listen to or see.

A simple solution would rely on computers to perform these tasks. For example, a song may be held on a computer in MP3 format, accessed from another computer and heard on its speakers. For digital video content that originates from a digital video camera or a DVD for example, loading it onto a computer will allow another computer to access it over the network and play it locally.

To able to hear the music through in-ceiling speakers or local hi-fi, or to view video on the nice plasma screen, will require some additional equipment. In audio terms, this role is already being filled by the numerous network music players that exist. Although most of them were originally developed to play audio stored in MP3 format from a computer, many can now handle different types of digital audio formats and even use portable music players as a source such as the Slim Devices Squeezebox, the Apple Airport Express, and the Rokus Soundbridge.

The Slim Devices Squeezebox digital music player

This kit generally requires a player in the room or zone where you wish to hear the music. The hardware will pull the audio from the source (usually a PC) and convert it to an analogue signal for amplification and hooking it the speakers. Some solutions have built-in amplifiers, other require either a local amplifier or powered active speakers.

For video, the solution is a little more complex. Currently, most video content is held on a central PC server and then accessed from computers in each zone. These then do a conversion to an analogue signal and send it to a TV using standard signal formats such as composite, S-Video, RGB or component. The local computer may be a traditional PC, for example a PC with the MythTV software application installed, or it could be a 'media centre' - a repackaged PC that has been made to look more like traditional hi-fi kit such as the Windows Media Centre or the Elonex Artisan.

The Elonex Artisan media centre

The local PC takes care of the digital to analogue conversion as well as offering the user the ability to pick content from the server. Some systems also allow the capturing of television broadcasts directly onto the server and act as digital video recorders. This also allows the user to schedule what programmes are to be recorded and watch them at will.

The biggest problem with video distribution currently, is that many of the sources are not broadcast quality. A DVD that has been ripped to the server may look great on a PC monitor but through a projector you notice the fact that some data has been lost in the various conversions that have taken place. A middle ground can be to use baluns that allow the signals to be sent over CAT5e/6 cable but are not IP based. Component-quality video is possible with these solutions.

The future of IP-based A/V networks

The future of A/V distribution is digital. Not only are users able to get content very easily into digital form, but with the rise in high-speed broadband Internet connectivity, much of the distribution will be digital. For example, there are now set-top boxes and televisions that are specifically designed to accept broadcasts over IP. Although not mainstream, the use of IP for broadcast is only going to grow. Distribution in the film rental market is also moving slowly but surely to network-based approaches - offering video on demand at the expense of the local video shop of course. The advent of HDTV broadcasting, whilst not IP-based, will also be another key event in the shift to digital.

Multimedia IP-based networking

The primary issues around IP A/V networking concern speed and digital rights management (i.e. copy protection). Networks have become fast enough to support audio distribution at even wireless speeds (see below), and the music industry is getting to grips with the balance of digital distribution and commercial benefit. The same movement is happening in the world of video.

Wiring for IP A/V

One of the key benefits to A/V distribution over IP is that wiring is simplified. Although it is technically possible to use a wireless network, especially with audio, experienced custom installers generally recommend sticking with a wired solution, ideally using CAT6 cable.

Although wireless networking has come a long way, it still has some fundamental limitations. The latest standard in mainstream operation, IEEE 802.11g, can only operate at a top speed of 54Mb/s, just of over half the 100Mb/s speed of a typical modern wired network. For MP3 audio this is fine, but it is much too slow for high-quality video content, especially with more than one concurrent stream. Modern gigabit Ethernet networks on the other hand, can operate at 1000Mb/s - the only inhibitor for the domestic market being the cost of the hardware, although that is changing over time.

Another drawback of wireless is its susceptibility to interference and reduction in performance simply from the physical structure of a building. There are also certain inherent security implications, but while a properly-installed wireless network should minimise many of the risks and implications, for data-intensive applications such as high quality A/V distribution, a wired network is still the best option.

Even for audio, it is worth considering the use of a wired network. MP3 is not the same as CD quality - the audio is compressed and quality is compromised. While you may not hear this through a portable player, low-end computer or custom install speakers, put an MP3 through a quality hi-fi system and you will soon notice the difference. While encoding CDs using something like FLAC requires more hard disk space and more network bandwidth, it is lossless and is worth it.

The cabling used is also worthy of consideration. CAT5e is the most widely used, being cheap and easy to install. CAT6 is up to three times more expensive but is worth considering. It is designed to more stringent standards regarding crosstalk noise, and therefore offers better performance, especially at gigabit speeds. For any installation considering future proofing for network distribution of high-definition broadcasts, a CAT6 network would be a key component.

The other main consideration of a network is the placement of the network points. Aside from any being set aside for more traditional uses such as for PC, phone, printer etc, it is worth considering placing points with traditional A/V outlets in the expectation of IP-based set top boxes and televisions. Even if these are not used for IP video distribution right now, they could be used with baluns for video distribution over the structured cabling.

Summary

The technology already exists to enable IP-based A/V distribution. The benefits are many:

* Single structured cabling topology supporting data, communications and A/V.
* Source/device agnostic. You can decide on the playback hardware at a later date.
* No loss of quality over long runs.
* Kit available now.
* Future-orientated technology.

This is not to say that more traditional A/V distribution technologies should not be used. Solutions such as those offered by Opus, Xantech and others are reliable, very cost-effective and not that complex to wire.

As far as the home media centre is concerned, work still needs to be done to develop a wide range of user friendly interfaces. While the Microsoft solution is very good, it is not perfect and better/cheaper solutions are still to come. Indeed there are currently few devices available that package IP-based technologies as objects that look and operate like consumer televisions or hi-fi. Although this is changing, it means that not every user may find completely digitally-based media to be completely intuitive.

What should not be overlooked however, is that the digital distribution market is growing. Any custom installation should be taking this into account and planning structured cabling to include the IP-based distribution of A/V.

Jeremy Aston is the founder of Reality Logic, designer, supplier and installer of smart home and office technology.

www.realitylogic.com