Video networks

To support multichannel production and multiplatform publishing, the broadcasting industry must gain production efficiencies. These efficiencies also need to be gained simply in order to allow people to be more creative.

The key area to enable this change is that of the layer 3 switch. This can partition off sections of the LAN on a packet-by-packet basis, therefore becoming an internal firewall. However, if a network is to be suitable for broadcasting, many more tough requirements must be met:

• The network must be secure from virus and other attack. Most large-scale commercial networks partition individual departments or network segments already. Broadcasters can use readily-available technology, but implemented to the highest possible standards.

• The network must guarantee performance. Many more buildings are having backbone gigabit Ethernet installed and managed, which is leading to an expectation that there is close to infinite bandwidth. For broadcast use, the addition of layer 3 switches forces a difference in architecture, which makes traffic flows much better defined and controllable.

• The network must be resilient. Network failures, which were once tolerated in the business environment, have now become less acceptable. With managed switches being so cheap to purchase, the overall management of a network for business purposes has improved. However, the needs of real-time broadcast playout require absolute 100 percent reliability, and may still depend on point-to-point serial digital video.

• The network must have a low mean-time to fix. This is a different concept to the business IT community, which normally expects a low mean-time between failures. What matters more to the broadcast production process is not how long it is between ‘going wrong,’ but how fast it can be fixed, as the next deadline will be looming.

• The network must be manageable. The use of layer 3 switches can provide business-level network control, which means that the equipment is cheap for the broadcaster to use. File transfer overnight using what appears to be low-capacity corporate networks can give great cost savings.

The message is that broadcasters can exploit the cheapness of existing LAN equipment rather than having broadcast LANs using expensive esoteric equipment. This means that less equipment is needed, and video material is available in places where it would not normally be seen. Likewise, the ability to use business IT servers rather than purpose-built ‘video’ servers is now possible as the performance for a given price is moving into commodity market levels. However, much care must still be taken in passing files over the public Internet, and full checking and multiple demilitarized zones should be employed.

There has been much discussion about the use of IP networks for files because this is what they are best at. Any stream has very stringent demands on a network. Streams have guaranteed bitrate and latency requirements, neither of which are easily accommodated by a collision-based, non-deterministic network protocol such as IP. The quality of service, however, is not necessarily an issue if the right interconnect is used for the right task. Non time-critical file exchanges, which make up the majority of TV usage, will run over Ethernet-type infrastructures. Time-critical streaming transactions will continue to occupy ATM pipes in the WAN domain, giving point-to-multipoint connections. Streamed video over IP will become established when telcos can provide the bitrate and service required economically.

While a few video-over-IP services are already coming into use for compressed streams, uncompressed video will remain as native SDI or HD-SDI until high-speed server interconnects are introduced in the local domain.

The effects of new broadcast networks will be dramatic. In simple terms, the developments of PC technology and network topology means that everyone in an organization can be joined up with a powerful range of tools. These can connect a production to every part of the team and all the resources they are likely to need.

Adrian Corcoran is director of operations for BBC Technology.