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UPDATED 10.7.09
ISDN lines
ISDN stands for Integrated Services Digital Network. All this information will concentrate on sound broadcasting.
It’s essentially simple - a digital phone line - but still using simple wires - that has enough capacity to offer speech at broadcast quality. There are two kinds of ISDN service in the UK:
the difference is the number of channels you can use: the first has two, and the second has 30. The channels can do different things at the same time, or they can be bonded together to give multiples of capacity. An ISDN2e line (the e stands for the European flavour) costs about the same as two analogue phone lines and is therefore affordable by all but the smallest organisation. ISDN30 is expensive and will be ignored from here.
Like a telephone, an ISDN connection is a direct point-to-point connection between your office and the broadcaster; each ISDN channel has a “phone” number and can be called by other ISDN equipment that can understand the digital data. You can’t speak to an ISDN line with an ordinary (analogue or mobile) phone. So being point-to-point the connection is secure and easy to understand, but you could still be “cut off” if the connection is broken.
ISDN is best supplied by BT: the service is consistent, national and the specialist engineers know what they’re doing. Other telecoms suppliers may know much less about it.
The line can be run straight through to your “studio”, or to a switchroom and then through your network to a port no more than 30m from the BT box. The box is similar to a telephone socket box, but there may need to an additional small piece of equipment too. See Location below.
But we’ve got broadband, who wants ISDN?
You may be thinking we have got a fast broadband connection, surely that would be better, faster and cheaper than having an extra, more old-fashioned connection just for broadcasting. The answer is, not really. Your broadband connection is like a funnel for all your internet traffic, but it isn’t really a direct connection to anywhere - except your ISP. Remember the internet is fantastically clever - the words in an email are divided into packets of data which are sent out separately, each with the address of where they need to go. They make their way separately, by the best route at the time, and may arrive at the destination at different times.
It’s like sending a class of children from school to the Science Museum - you give them each the address and wave goodbye at the school gate. They each make their own way, by different routes and modes, and will all arrive at different times, in a different order and some maybe not at all.
It would be quicker, safer and more organised to send them all together in a coach from the school gates to the museum. That’s what ISDN does - a direct, secure, point-to-point connection.
IP protocol equipment
There are now many pieces of equipment which use the IP protocol for sending voice to broadcasters, but they haven’t yet really taken off. There is an EBU standard to standardise the data stream but broadcasters haven’t yet jumped at the new technology. Many contribution units offer ISDN and IP technology which does offer a future-proof solution but they are expensive - having to have both technologies in one unit. There are rumours that BT will cease new ISDN installations in the next year or two, but nothing is confirmed yet.
The public internet is not an ideal way to send critical, timely data. The first problem is that the upload speed (from your network to the outside world) is much slower than the download speed (from the outside world into your network). Upload speeds may be as low as 256kbits/sec, while the download speed may be 8mbits/sec or more. This is why broadband is often known as ADSL, where A means Asynchronous - the upload and download speeds are different. You can can get DSL with much faster upload speeds, but it is more expensive and not supplied by every telco. After the packets of data have left your network they then have to compete with every other piece of data in the system, from emails to YouTube video, before they reach their destination - tired, cranky and out of order - just like us.
A further problem is that IP systems may need to go through an intermediate SIP server which delays live data even more; SIP servers come into their own when transferring non-live material for later broadcast.
So ISDN still has legs, because - compared to IP - it is relatively cheap and straightforward. An unlikely conclusion!
ISDN broadcasting equipment
Once you have your line you need to connect your broadcasting equipment.
This will usually be a fairly small box combining a terminal adapter (TA), codecs, input/output ports and bits and pieces to adjust levels etc:
- the terminal adapter simply sends out the signals in the right way to be understood at the other end, and enables you to call another ISDN installation
- the codecs are the languages your equipment can speak and understand - there’s no point in speaking Greek if the other end only speaks Chinese. There are several codecs commonly used in broadcasting
- input/output includes inputs for your microphone and output for your headphones, and a knob to adjust the volumes
The most commonly-used codec in the UK for speech contributions is G722. It is used by every BBC installation and has very low levels of delay, so your speech and the interviewer’s are transmitted and decoded virtually instantaneously. It is good for live interviews - or two-ways. Other codecs you may come across are MPEG Layer 2 which is good but much slower to encode and decode, and APT-X, still favoured by commercial stations but not used by the BBC. Almost all ILR stations can take a G722 contribution, but they may not realise it.
The trick is to get the broadcaster to call you, then:
- they pay for the call
- your equipment recognises the codec they are using and switches automatically to the same one
- any difficulties in routeing the connection within their fantastically complex audio switching networks are their problem, not yours
Location
You will need to position your broadcasting equipment somewhere close to an ISDN box. Normally BT will install the box where you wish - it comes into a building on normal phone wiring (a pair) and is taken to where you want it to be terminated either on new direct wiring or through a building’s phone cabling ducts. Normally it will go to one place and that’s that, but it is possible to install the BT box close to an office or floor ‘patch panel’ from which the computer network is distributed. A patch panel is typically in a ventilated cabinet, possibly in a special small room to which the IT people have access. You can link the BT box to the patch panel and then distribute the ISDN signal around the network to whichever data port on your network is most convenient. The broadcasting equipment is then plugged into a data port (like a PC) - this has the advantage of being able to move the ISDN signal from one port to another - ie one room or area to another - to deal with different circumstances, though there are distance limitations on how far the signal can travel on the Cat 5 network; you also need easy access to the patch panel.
The broadcasting equipment itself needs a table or desk to sit on, but that desk could be in an open office, in someone’s personal office, in a room set aside for broadcasting, or in a ’studio’ of your own. A studio need not be very elaborate and there is an overlap between a room set aside for broadcasting and one called a studio. Studio certainly sounds better! The room should be quiet, it may have sound deadening material on the walls to absorb echoes and give a dead feel to the acoustic, it may have a window in the door or wall and/or a special sign so people can see when you’re broadcasting, and it should be cool enough to be used for an hour in the summer with the door closed but without noisy air conditioning.
One word on finding a quiet room - remember it must be quiet both for noise coming from inside the building and from outside. Check by going into the room, close your eyes, and making a mental list of all the sounds you can hear for at least two minutes - listen for your colleagues laughing, doors or filing cabinets opening or closing, phones ringing, traffic, banging, aircraft, children, sirens, factories, air conditioning, computers - you’ll be surprised how much you can hear. It’s a very noisy world.
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