Modems on Voip

[hillbilly1]

I found out something yesterday, Energy management modems do not like Voip! Installed an energy management power monitor at a big box store, the modem shares a line with a fax machine, the modem can only be accessed in a predetermined time frame, so it does not conflict with the fax machine. The modem would connect sometimes, but the majority of times would not, or would disconnect shortly after connecting. Fax machine works fine, no noise on line, after four hours, the manufacture decided that the modem must be bad. Came back and replaced the modem, still had the same problem. Manufacture checked settings and firmware, and could not find any problems. This led me to believe there was a problem on the telco end. Went all the way back to the demarc at the other end of the building, and found that number did not exsist at the demarc! Got to digging, and found phone line originated from a computer. Voip! Hi jacked an actual hard wired line, the modem started working perfectly! Apparently Voip is not good for faster speeds like a computer modem. Works fine for fax lines though.

 

[dbuckley]

Fax working over VoIP isn't because fax is slower, its because (most) VoIP components are designed to specifically carry fax signals, google for T38 or RFC3362.

If it weren't for T38 then fax would fail just like the modems did.

Of course, there is a bit of irony here, because that modem link wants to carry data to some remnote place, and the internet connection behind the VoIP box is actually designed for carrying data... pity the EMS couldn't just have an internet connection to connect to wherever it's phoning home to.

 

[hillbilly1]

It has an ethernet connection, but the customer does not want them behind their firewall or on their network.

 

[AV ELECTRIC]

I have a less complicated issue with my voip but it sounds the same. at my residence I tried to hook up my voip line to my dish network receiver it will pick up dial tone and connect but will disconnect shortly there after . Oh well I guess I pay the 5 dollars per receiver since my voip system will not complete its connection.

 

[zbang]

Expanding on what dbuckley said, VoIP needs less bandwidth for voice than usual (<32kbps v 56kpbs) is they're trying to encode the voice, just as a cell phone does.. The encoders are expecting voice, including periodic silancees, so when they get the seemingly complex modem signals that run without a break, they throw up their hands and give up. Fax works because the VoIP terminal figures out that it's a fax, demodulates the fax signal, and sends the bits 'digitally'. The other end remodulates the signal for the receiving machine.

BTW, that's why the Dish box has problems.

 

[hillbilly1]

I have a less complicated issue with my voip but it sounds the same. at my residence I tried to hook up my voip line to my dish network receiver it will pick up dial tone and connect but will disconnect shortly there after . Oh well I guess I pay the 5 dollars per receiver since my voip system will not complete its connection.

Our modem was doing the same thing, we thought maybe there was another modem on the line, because the handshake tones were different from what the manufacture was used to hearing, apparently it was the Voip.

 

[hurk27]

Not sure if this info was true, but I was told that it is because VOIP compresses the audio signal to save on data rate, and many VOIP modems can't discern between data or voice and tries to compress it but causes errors when it is de-compressed at the other end? Most Broadband suppliers will work around this by supplying a separate DSL or cable modem to allow the affected equipment to be ahead of the firewall, and some even have VOIP modems dedicated to data transfers, I would check with the Internet supplier to see if they have a cost effective work around.

I have a job coming up on a gated community where I have to install a modem at the control box to the entry, and at the office of the property management office, so they can remotely set new gate codes for new residence moving in/out, but the office is VOIP phones and the gate is a land line, and these will be older V.46 modems, set @ 1200 baud WIN (software) modems don't work. so it will be interesting

 

[zbang]

[also posted in the low voltage area, it's relevent in both]
Just to flog a dead equine- VoIP is Voice over IP, not "any audio signal" over IP. The only reason that a fax works is because the terminal adapters specifically recognise fax tones.

 

[betcher78]

One thing which would be possible with a little more hardware. Would be to create a DMZ or demilitarized zone on one port of your router. connect this to another router , which would connect to controller . Or ask for another static IP from DSL or CABLE provider. use a switch before the original router , run original and new router to that.
on one PC in office , install a second network card from new router , specificaly for controll of monitor system which is tcpip capable.

depending on how that gate interface works, it might also just have a straight rs232 or 485 interface? most do . i used an ethernet to rs485 converter a while back. ill try to find that. you can use one at each end. or plugged into network where you can tell each converter who to talk too using web interfaces in each converter. that was a while ago , ill try to find documentation and product links.