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Converting to VoIP

D

dtube1

Hi all. Next summer, we're converting over to a VoIP system for the entire facility. Aside from begging the CIO to implement a decent-sounding codec for the system, what do I need to spec in the new system to keep my analog POTS hybrids in the studios operating at a reasonable level of fidelity?
-D
 
You'll order copper POTS lines from telco to go to your hybrids and not use the VoIP system for on-air calls at all. ;D

Does your VoIP solution offer ATA's? The system we're about to install at my day-job doesn't...it only offers four ATA ports. We have 12 POTS lines just to cover IFB and PL needs (and that wasn't enough during the last election cycle!) Add six lines on our TS612, another one or two in interview booths, and six fax lines (yes, you'll find fax over VoIP doesn't work very well)...

One place I know that converted to VoIP went with the JK Audio Broadcast Host (I think) that goes in-line with the telephone handset.
 
Make very, very sure that the system supports CPC. CPC is short for Calling Party Control, but does have other names as well, so don't get stuck if the vendor doesn't know the name. Describing what it does is more important.

Basically, when the calling party hangs up, the system detects this and, briefly, turns off the battery voltage on your line. This brief battery interruption is the method most automatic phone couplers use to auto-disconnect. If the analog ports don't support CPC, you will find yourself buying expensive call progress decoders that are never as good as CPC. Most digital systems, surprisingly, leave out this very important feature which is standard on 98% of the POTS lines around the USA. There are good systems out there that have CPC so ask first and don't even consider buying a system without it.

Regarding quality, make sure that the system doesn't regenerate the DTMF tones. If it does, it will frequently mistake some voices for tones and start beeping from time to time in the middle of conversations. It's quite annoying.
 
Lots of considerations to this.

1) Insist that the VOIP system has direct bandwidth (dedicated T1, Metro Ethernet, etc) to the VOIP dial-tone provider. Running your VOIP across the Internet to your dial-tone provider is unacceptable for broadcast use.

(if you can't do so you will need to do extensive pre-testing, probably with multiple dial-tone providers till you get one that has few enough IP-hops to work reliably)

2) You are correct to be worried about codecs. "mu-Law" is the standard phone codec used on synchronous networks, so that is the one you probably want. Delay is a concern as well - packet size is an important variable here. You can read up on codecs on the Telos and Comrex white papers.

3) Since this is being forced on you I suggest you should make lemonade. I would strongly consider scrapping the analog POTS interface stuff and get VOIP-capable hybrids. This gives you the advantage of an all digital connection and removes all hybrid-null issues on your end. This is also true of ISDN-based talkshow systems, but you can bypass that generation.

You might even see if the IT folks can help with equipment costs since their ROI will be coniderable. It will also prevent the concerns in #4, below, so it could be worth their while.

4) If you must go with the ATA (Analog terminal adapter) approach you will need a considerable testing phase to evaluate the options. Most people designing these things have no experience at all with the intricacies of analog interface design. Poorly designed interfaces can cause all sorts of hybrid leakage and other problems. "CPC", AKA "disconnect supervision" is important as mentioned by another poster.

5) If you are in a large metro area you will need to have some very frank discussions with the dial-tone provider if they are to provide contest lines. Even if all is OK at their end, there are considerations at the station end. An important and very real question to ask is if the Sales staff are going to be able to make and receive calls when a contest is going on.

6) If you head my advice and replace your talkshow system hardware, you will also get the advantage of significant engineering resources at the equipment vendor. You should schedule a conference call with the equipment vendors Application Engineer and your IT department to start consideration of all of the above. The contact at Telos is Joe Talbot. Not sure who the best contact would be at Comrex, but Tom Hartnett can steer you to the right person.

Rolf Taylor
Twins Ace Hardware
 
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