Designing Multimedia Networks

Moving voice and video over any data network can be a challenge, if you’ve ever sat through a stuttering video conference you’ll appreciate that you have to do it well.     Fortunately it’s becoming more of a reality nowadays with efficient compressions techniques, high bandwidth networks and of course QoS.   Compression is probably the most important factor as it radically reduces the volume of traffic that needs to be transmitted over network links.

Genuine multimedia networks are rarer than you would think, and indeed some of the best which have integrated ATM (Asynchronous Transfer Mode) can be extremely fast.   One of the most important factors apart from the increased speed ATM can bring to both WAN and LAN networks is it’s support for QoS.   This guarantees a certain bandwidth and performance levels for the multimedia connections, although this has to be reserved to be effective.  Not only can administrators reserve their multimedia requirements but they can also set up virtual circuits to separate their video conference, multimedia or voice calls.   Although it should be noted that this will require either ATM compatible applications, adapters fitted to the workstations or software that emulates ATM on standard network interface cards.

Whatever technology is incorporated the main issue with adding multimedia applications to a network is simply the traffic load.  It’s pointless letting users have access to real time multimedia applications without a very fast data network and some sort of QoS guarantee.   The network also needs the capacity to provide these guarantees without affecting the rest of the normal data traffic.    Capacity planning is crucial and until this is carried out you will have little idea how even a modest set of multimedia applications will effect your network speeds.

For any long term use there are a variety of techniques which can radically boost network performance for multimedia.  Core switched networks which connect to existing departmental hubs is a start and these can be upgraded to provide switched services to different departments as required.   Any videoconferencing equipment should be connected directly to high performance switches, on no account should the traffic be allowed to broadcast out through out the network through a simple hub or repeater.  Most high performance networks now try to standardise on Gigabit ethernet although often this can be slowed by legacy network hardware. Iso-Ethernet is an emerging technology which can incorporate  voice and standard 10 mbit ethernet on the same cable.

There are a variety of methods and technologies which will provide quality of service over existing networks if you don’t have access to ATM.  In fact often it is easier to use one of these bespoke methods as ATM does require modification and support in all applications, transports and software.  A technology called RSVP (Resource Reservation Protocol) has been developed by the IETF (Internet Engineering Task Force) which allows any IP host to request directly a specified amount of bandwidth on a network.

Further Reading