Articles and whitepapers

Multiroom Video Over CAT5 (3/4/2006)

By Chris Skelton, Bluedelta Design

The age of a single television in the lounge, with the whole family huddling around it after dinner, has long passed. The diversity of programming now available makes it extremely unlikely that any modern family will be able to agree on what to watch. Long gone too are the days when the bedroom had just a 14" portable. That's now the 28" widescreen that occupied pride of place in the lounge - until the new 42" plasma became a 'must buy', and forced it into early retirement.

Flatscreen TV

While we have entered the age of plasma and LCD TVs, of bigger and better pictures, and of looming high definition, it is strange that many multiroom video systems are still being installed using UHF over coax. How often have you seen a nice flatscreen with a grainy picture - just because the last few meters of the link are an ancient bit of coax with a traditional 'TV aerial plug' at either end?

It is the 21st Century, so what about a wireless video sender to improve the picture? To anyone who has not seen one of these in operation, they can look very attractive. But they are prone to the 'occasional' drop out of signal, or blizzard across the screen when the microwave is turned on. If you are going to invest in decent audio visual equipment, you need to ensure you make the best use of the pictures everywhere.

Why use CAT5?

There are a couple of ways of achieving high-quality output from your DVD to another device - the most obvious being SCART cables, although 15 meters of SCART is not only costly, it is also hard to hide. The industry has been 'playing' with CAT5 for some time, primarily in the field of security video or remote computer monitors, but it is only recently that systems have begun to emerge that are either economically viable or truly tailored to the domestic environment.

Third-generation video-over-CAT5 systems address these issues by making use of the properties of the twisted pair wires, namely providing a high degree of noise immunity both to external sources of interference and to crosstalk between the separate signals within the cable itself. Provided the relevant signals are injected at the master sender, and received at a slave receiver in a true differential manner, then external noise is cancelled.

The main problems up to now have been prohibitive cost coupled with limited ability and limited fan-out. Today's third generation video-over-CAT5 devices however, are addressing these issues and retailing at well under half the price of the previous generation devices.

Video-over-CAT5 generations

The three generations of video-over-CAT5 can be described as follows:

Generation 1 (G1) - passive BALUNs. This is really a legacy from the CCTV industry, and while useful in some applications, it is only applicable to single point-to-point links, i.e. fan-out = 1. It also suffers from very limited range and bandwidth.

Generation 2 (G2) - early active systems. Some of these are very good, but very expensive too. They often pass video very well, but some have no provision for audio, most have no provision for remote control return, and surprisingly, none at all have the ability to pass on/off/widescreen information to the remote displays. In addition, G2 systems share a limited maximum fan-out of 12 or less.

Generation 3 (G3) - current state of the art. This is truly user-focused, and can supply a seamless audiovisual experience to each outlet. A G3 system will convey CVBS or S-video along with stereo audio and full widescreen signalling, so each outlet essentially behaves like a direct SCART connection. A G3 system should be modular, and able to operate with a fan-out of 16 or more.

G3 systems are designed so that the entry level cost of a simple point-to-point system is low, but the system can be expanded when required. So, if the user wants to have their AV source equipment in a separate communications room away from the viewing device for example, they can expand the system to have a second or third viewing location, as well as the ability to watch from one of several AV sources while still being able to control from a remote location. All should be easy additions after the initial system is set up.

Video-over-CAT5 components

Video-over-CAT5 systems can be broken down to the following key components:

Master devices
To start with, you will need to interface your video equipment to the CAT5 network, and pass back any remote control information from the remote locations back to the source equipment. In its simplest form, the Master will be a single SCART interface.

Distribution Hub
In the simplest star-wired systems, this is a compact unit similar to, but not the same as, an Ethernet hub. It performs the dual function of video/audio distribution from a Master device to multiple Slave devices, and of returning remote control information from the Slave devices to the Master.

The Bluedelta Milestone distribution hub

Router
This is required for more complex systems where multiple sources need to connect independently to multiple displays. Ideally, this will incorporate the input interfaces, and provide independent outputs to the remote TVs. This all sounds very nice, but there can be significant operational difficulties associated with the user interfacing of routers, which none of the current systems have addressed convincingly.

Slave devices
Finally, you will need something to connect to the remote TV. In its simplest form, the Slave device is a compact unit which can either plug directly into the television's SCART input or connect to it via RCA. Of course the Slave should have an infra-red pickup in order to relay remote control commands back down the cable to the source.

The Bluedelta Milestone Slave unit plugged into back of a remote flatscreen display

Infra-red pickup on front of flatscreen, connected to Slave unit at the back

What about high definition?

All the components required to implement HDMI in multiple locations will need to be very different to those used for current systems. Unfortunately there is no crossover between the technologies, and there is no solution in existence or in prospect that will deal with both systems together. The best solution is to allocate a second set of CAT5 cabling to be used separately for the HDMI link. With CAT5 cable being low cost, it may be worth running two cables to a suitable face plate at the time of your initial install, as future-proofing.

Wallplate with two CAT5 sockets

While HDMI is coming, and several companies are working on CAT5-based point-to-point links, the very high bandwidths required for HDTV will seriously limit the transmission range available. In addition, the complexity of the HDCP content protection system will likely make true multi-outlet networks impractically expensive for the foreseeable future.

Proper planning

No matter how good your equipment is, it will be let down by inadequate infrastructure. Remember that you may need to use many video sources, not all of which will be equipped with the same interface, so ensure you work with a modular system that offers interface adaptation.

A multiservice wallplate

Future developments

The upcoming fourth-generation (G4) systems will be based on third-generation technology, and should become available in early to mid 2007. They will support full RGBS and/or YPbPr and where routers are used, the control issues will have been addressed. G4 systems will be truly user-focused, supplying a seamless audiovisual experience to each individual outlet.

Conclusion

A properly-installed video-over-CAT5 system will be reliable, use suitable interconnect fascias and provide the best possible service to all outlets. The inherent noise immunity of CAT5 cabling will stand it in good stead with the growth in wireless home gadgets. It will be simple to install, especially in houses already flood-wired with CAT5, and will lend itself to simple upgrade and expansion, whether to keep pace with new technology or to simply add a couple more outlets.

Chris Skelton is the Managing Director of Bluedelta Design, designer and manufacturer of the Smart Scart automatic SCART switch, Phantom PVR, and Milestone video-over-cat5 cable systems.

www.bluedelta.co.uk