Page 4
Page 4 |
|
When VOIP becomes mainstream, it will probably be delivered over xDSL lines. Like ISDN, xDSL is a way to transmit digital data over the Telco’s existing copper wires. Because it is a newer development, it offers higher bitrates – ranging from 512 kbit/s to 6 Mbit/s.
The term xDSL specifies a Digital Subscriber Line using any of a number of technologies. ADSL and HDSL are the most common variants, and there are around a dozen incompatible implementations. Incidentally, some people consider ISDN to be an xDSL mode.
ADSL uses fully reliable ATM as its underlying protocol, not IP, so it naturally can work to provide ISDN-like voice connections without the problems described above for VOIP. But that is not how it is being deployed today. Most often, on the user terminal box there is an analog voice port and an Ethernet IP jack for the Internet – no digital connection to the voice network. It could be possible to use the Internet for VOIP, but this would come with all the usual problems.
With the rise of ADSL, an interesting question (in the USA) is “What is the future of ISDN?” Some Telos clients have reported to us that their Telco is trying to steer them to ADSL when they call to order ISDN lines, the Telco rep being apparently convinced that the only application for ISDN is Internet hookups, for which ADSL is undoubtedly superior. Until VOIP becomes routine and reliable, it is unlikely that ISDN will go away. That’s because it offers the only way to get a reliable and normal audio quality digital connection into the voice phone network. One possible direction is what we see in Europe, where some ADSL terminals have ISDN BRI jacks.
When radio studios came in pairs for an AM/FM facility, a dozen studio Telco lines was generally enough. But the now-common consolidated plants could use 100. With this number, telecom providers are certainly going to want you to take the service on T1s or ISDN PRI. Which should be just fine for you, as well, because you will get all the advantages of digital connections.
There will also be economic benefits. A channel on a T1 costs less than an analog pair. Per-minute long distance costs can be lower, if you bypass the Telco and go straight to your LD carrier. Because the pool of lines is shared to all studios, you pay only for capacity necessary to support the peak demand generated in the aggregate. Because all studios are not likely to be using all lines at the same time, this should be a lower number than the sum total of all lines appearing in all studios.
Generic PBXs will not do for our broadcast application – they just don’t have the features necessary. For example, while lines may certainly be shared to multiple phones, there is no way to switch groups of lines from studio to studio. There is also no way to connect computers for call-screening applications. On the audio side, there is no adaptive hybrid or professional audio outputs. Usually, there is only one or two “Music on Hold” inputs for the entire unit, while we need one for each studio. While you could use a PBX to derive analog lines for the studio telephone interface gear, it will be far superior to make a direct all-digital link. So we will need something like a PBX, but specialized for broadcast.
What we need for a modern broadcast studio telephone interface system is:
Support for T1/E1, PRI ISDN, or BRI ISDN, with interface directly to Telco lines, or via PBX so lines can be shared with office phones
High line capacity – perhaps 96 lines (four T1s)
Multiple studios and producers, etc. can share the lines
Program On Hold for each studio
Users may switch line groups among the various studios according to need
Caller ID
User interface that is easy to learn and use, and minimizes errors
Allows connection of computers over TCP/IP for call screening, production
Remote management and diagnosis, over Internet
High-quality audio and high-performance hybrids
Digital connection to studio audio gear (AES/EBU or Ethernet IP)
Ready for future, such as VOIP
The first point is clear: The system must plug without hassle to all of the usual modern digital Telco interfaces. You can choose to have the studio system to connect directly to the Telco lines, or via the PBX so that the lines may be shared with office phones. High-end PBXs support T1 or ISDN on the station side, so that can be used as a link between the systems. Because the path in the PBX is all-digital, there is no worry about audio degradation. With most PBXs, lines may be easily shared between the business and studio systems, including display of status and transferring from one to the other – something that has been difficult or impossible with older systems.
The ability to on the fly reroute set of phone numbers to different studios, as operations require, is an important requirement. The trend in larger consolidated facilities is 'generic rooms' used at different times of the day for different shows. Even in smaller plants, you may want to have a bank of call-in lines for a popular morning show that is re-used on a different station for requests at night, for example.
• 
