| My main exposure to ISDN in Australia was in radio stations. In Australia, we had an ISDN2 product (BRI) which gave us that 128Kbps bitstream. Hardware boxes from brands like Musicam Prima, Tieline and Comrex would allow transmitting a bi-directional MPEG2 audio stream. When I used to dial these things, you’d hear a low-bitrate stream first for a few seconds before the 2nd number would dial and you’d get that full 128Kbps. Different brands of codecs were theoretically interoperable, subject to the settings and codecs matching. I remember the Tieline codecs probably sounded best because they had their ‘MusicPlus’ codec (which I think was actually AAC+ under the hood). But most other codecs were only MPEG2, so you were stuck with that. We used to use these for outside broadcasts, backup links between the studios and transmitter site, and links to other broadcasters (e.g. the TV news presenter dialing in to tease the nightly news headlines). Even after the internet was well and truly established, ISDN was still used a lot for this because it was ‘standardised’ and also a pretty much guaranteed bitrate - whereas ADSL might give you a couple of megabits but with no guarantee you’d have that between your two locations at all times. When you need low latency two way conversations, you can’t just dial up the latency and keep re-transmitting packets until they arrive. The local telco used to be able to install these fairly easily on a temporary basis so you could do a broadcast from a temporary location (e.g. local advertiser books a broadcast at their store). You couldn’t really get a temporary internet connection put in at the time. You could get stereo audio both directions, but often you’d use the left channel for your program audio, and the right channel for an intercom in everyone’s earpieces. So long as you played the music from the studios and just fed the mics down the ISDN from the remote location, the quality was passable. We also had ISDN10/20/30 (PRI) for general telephony. I interfaced these to SIP PABX’s a few times with Patton boxes, but the docs were always for T1 not our E1. I don’t really miss it, but it’s kinda cool in retrospect. |