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VoIP and Dialup modems

D

Divarin

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Joined
Mar 9, 2019
Messages
566
Location
Cleveland, OH
Has anyone here had much luck using dialup modems over a VoIP service? I have been trying to access Hidden Reef BBS which is a TI-99/4A BBS that's dialup only. My VoIP service is AxVoice. Recently my wife needed to send a fax to get some medical documents and I was able to send the fax using a fax modem over VoIP but it took about 5 minutes to send a single page.

When I try calling into a BBS (tried Hidden Reef and Cottonwood) I can get connected but it takes upwards of a minute from each keypress until I see the echo. Although the data coming downstream seems to come in pretty quickly.
I've tried 300 baud, 1200 baud, 2400 baud, and up all with the same results.

So a couple questions:
1) Is there any particular modem settings I can try that might improve things such as disabling compression, changing the flow control, etc... ?
2) Is there any particular VoIP service that is known to work better with modems than others?

I don't think I'd go out and get a VoIP service just to call an occasional dial-up only board, but since VoIP is relatively cheap I'm probably going to have one just in case there's issues with our cell phones, we need to send a fax like the other day, and if I'm going to have VoIP anyway I might as well have a service that I can use to call into BBSs with.
 
Basically no, its generally hopeless. While real "analog" phone lines are likely using a SIP like technology in the middle, the technologies used in the PSTN use different codices. Their IP transport manages latency, jitter, and packetization that permit a high symbol rate and prevent loss of sync between the modems. Your consumer VoIP service ( lossy codex ) and public internet connection ( high latency, high jitter, no QoS ) won't.
 
I had a reasonably decent VoIP+modem experience with NetTalk several years back, as further described in this thread.

Key things to look for (that I presume are still applicable today):

Concerning the ATA device and VoIP service:
- Use of a G.711 CODEC
- Packetization of 10ms - 20ms
- Ability to disable the echo canceller and voice activity detection / comfort noise generator
- Fixed, 200ms jitter buffers

Concerning the modem:
- V.34 and V.42bis compatibility
 
ISTR making an international dialup connection some years ago, using a calling card arrangement, where the modem could negotiate V90 speeds (i.e. >33.6k) but the connection couldn't actually support that speed. Had to modify the modem init string to restrict to 33.6k/V.34 and we got a working connection.
 
mdog69 said:
ISTR making an international dialup connection some years ago, using a calling card arrangement, where the modem could negotiate V90 speeds (i.e. >33.6k) but the connection couldn't actually support that speed. Had to modify the modem init string to restrict to 33.6k/V.34 and we got a working connection.
Click to expand...
do you remember what init string you used to restrict it to 33.6k/V.34 ?
 
Well I have had some luck today I don't know if it's just random or what.
Using HyperTerminal I switched the "Connect Using" dropdown from my modem to just the com port the modem is on (com 4)
I did this because I wanted to go into terminal mode and start sending AT commands to the modem, so I could experiment with some settings. I wasn't able to find any useful registers I could change and the manual for the modem (on CD) doesn't describe anything but the basics.
But then I decided while I'm that mode I'll go ahead and dial up hidden reef. this time the connection was pretty quick both upstream and down. I don't know if it's just because my VoIP is in a good mood today or if using "Com4" in that dropdown had any effect.
 
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