Since the earliest days of radio and television telecommunications have played a part in the business of broadcasting – getting material from one place to another and then on to the viewers and listeners.
It’s a relationship that continues with the coming of new multimedia and wireless broadband technologies and is likely to become more complicated and interdependent as broadcasters look to reach new audiences through mobile devices and telecom service providers supply programming to the consumer as well as providing the links.
Going back to the pre-digital transmission-distribution days of the 1950s and 60s, line interconnection, as it was formally known, was the province of a usually large, specialist department within broadcast organisations, with connections provided by the state-owned telecommunications company.
From the 60s to relatively recently the BBC used permanent programme (music) circuits, with backups, which also provided wide-band (approximately 10kc/s) one-way channels for comms. The vast majority of circuits used by the BBC back then were owned by and rented from the Post Office (PO). Short-range radio links supplied by the BBC itself were used in situations where PO lines could not be obtained or were too expensive.
The telecoms side of the PO became British Telecommunications (BT), which was privatised in the 1980s. BT continues to supply circuits to broadcasters, both radio and TV, in the commercial sector as well as for the BBC. BT provides the network from play-out centres to the transmitters for Freeview, the digital terrestrial TV (DTT) platform, while in radio its KiloStream and MegaStream Ethernet systems are used by many UK stations.
John Ellerton, solutions consultant with BT Media and Broadcast, says people are now looking at IP carrier networks. Because of this, he says, BT is considering new technologies based on multicast RTP (real-time transport protocol), which sets out standardised packet formats for carrying audio and video on IP networks. “These are tolerant of network interference, like jitter, and are able to switch packets to guarantee quality,” he explains. “Audio needs less bandwidth than video so in theory these should be easy to put together.”
Ellerton comments that customers are encouraged to use managed media networks with IP codecs to guarantee the bandwidth necessary for broadcast work: “These have a class of service, so we can manage the IP stream to keep latency down for both studio to studio and studio to transmitter links.”
This allocated bandwidth is managed using MPLS (Multiprotocol Label Switching), which speeds up network traffic by establishing a specified route for a set sequence of identifiable data packets. As it is multiprotocol it can operate with a variety of formats, including IP, ATM (Asynchronous Transport Mode) and frame relay network protocols.
BT is currently rolling out its 21CN (21st Century Network), which, amongst other things, will take the national phone network to digital IP operation and provide faster, higher quality connections. In particular it will move beyond voice over IP (VoIP), as characterised today by Skype and similar technologies.
Ellerton says 21CN will play a part in BT’s UK media network for linking between studios and on to transmitters, although still on a managed basis. “We want to make use of a global network and modern codec technology to carry media files and emails but amongst that be able to also have IP-based audio.”
All this is sounding the death knell for IDSN (Integrated Services Digital Network), which took over from expensive permanent and booked circuits and brought lower cost contribution and distribution options to the radio sector.
While countries like Sweden are moving away from ISDN in favour of IP and MPLS networks, Ellerton says there is concern among ISDN users in the UK that it will disappear soon but the reality is slightly different: “People are paranoid that ISDN will be turned off but at the moment we don’t have a plan for that. ISDN will be around for years to come.”
Ultimately, however, ISDN will be superseded by emerging technologies, including AoIP and LTE Broadcast on 4G networks. Ellerton says there are still things to be careful about, particularly that old “bone of contention” jitter, but it is clear the Internet will be a new backbone for broadcast communications. And while managed networks are still seen as the ideal, even public connections could play a part. “I’m sure there will come a time when the open Internet will be good enough but we still need connections to transmitters to be rock solid. But things like that will occur,” Ellerton concludes.