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-   -   Finding old ISDN PRI terminals? (https://www.vintage-radio.net/forum/showthread.php?t=176910)

non-entity 22nd Feb 2021 1:04 am

Finding old ISDN PRI terminals?
 
So I'm trying to purchase some ISDN PRI phones. Preferably for E1/EuroISDN networks, but I can't seem to find any. I've been googling for days and all I can seem to find are ISDN BRI phones and VOIP systems. The only PRI related products I can find for sale are trunking cards.

Did anyone actually make PRI/E1 terminals. I have a few old H.320 videoconferencing phones, but they utilize strange interfaces and it will require a lot more research / work to get them working. Ideal I'd like some simpler PRI phones for this project to play with? Did such phones ever exist? Where can I purchase them or at least what manufacturers should I look for?

cmjones01 22nd Feb 2021 9:34 am

Re: Finding old ISDN PRI terminals?
 
The only PRI terminal I've ever encountered was a card in a Cisco router, used to support multiple simultaneous dial-up internet connections. It was useful because it supported V.110 rate adaption, which enabled fully-digital connections from GSM mobile phones. I remember very well that from pressing "connect" on the phone to having a fully configured, working mobile internet connection (albeit at 9600 baud) took 6 seconds. Pretty impressive, even today.

Otherwise PRI connections tended to go to the telephone exchange in the building, not to individual phones.

Chris

non-entity 22nd Feb 2021 2:44 pm

Re: Finding old ISDN PRI terminals?
 
Thanks, that sounds about right. I ended up doing some more research late last night and it seems like a typical config was to have different PBX's (BRI, IP, analog, etc.) connected to a central PRI switch, along with serial terminals (mostly V,35 or RS449, in fact the H.320 videophones I mention use one of the two)

G6Tanuki 23rd Feb 2021 6:47 pm

Re: Finding old ISDN PRI terminals?
 
Yes I've only come across ISDN PRI stuff in 'commercial' gear - PBX and what in the 1990s was expensive Corporate-quality videoconferencing.

It was a bit-of-a-thing a couple of decades back as a way to replace a 'snake' of analog copper lines into a small-business or a radio-station but they generally got decommissioned [along with the 2b+d basic 64K ISDN circuits to 'outlier' studios] once "Metro Ethernet" became cheap.

Sparks 23rd Feb 2021 7:44 pm

Re: Finding old ISDN PRI terminals?
 
I seem to remember ISDN was something that Canford Audio were pushing more than twenty years ago. One of its applications was enabling stay-at-home radio broadcasters the means to connect their home studio to the appropriate 'hub' of whichever radio station they were on that day.

G6Tanuki 23rd Feb 2021 8:44 pm

Re: Finding old ISDN PRI terminals?
 
Yes what Canford was pushing was "Basic Rate" ISDN: two separate 64Kbit/sec channels (56Kbit/sec in the US) and a background 16Kbit/sec 'data' channel. Perfect for providing "CD Quality" digital audio between a home-studio and the actual transmitter-infrastructure. The likes of ClassicFM could not have launched without it!.

"PRI" - Primary Rate Interface - ISDN was much heavier-duty: you got a 2.048Mbit/sec pipe [1.536Mbit/sec in the US] channel that could be subdivided to provide loads of separate voice-quality audio channels [for speech-phones] or multiple sub-channels could be 'aggregated' to provide something like 320Kbits/second which was just-about-adequate for videoconferencing.

As noted upthread, this was generally done using 'professional'-grade hardware: I remember some of the Cisco Call-Manager gear from the last-century came with options for PRI cards, and Codian also offered a range of hardware-codecs that could rate-translate between popular US and UK videoconferencing bit-rates.


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