HOWTO: Successfully getting TTY working over VoIP

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Mark Rejhon

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(This is for technically-experienced people)

I know we all have videophones, IP-Relay, and other technologies that replaces TTY. However, some of us still need to also use TTY sometimes.

Just wanted to say I got my TTY working perfectly over a telephone line connected over VoIP.

You need the following:

1. Really good ISP with good ping latency. (I recommend an ISP that is "XBOX LIVE recommended" or has good reviews for latency on places like dslreports.com -- those often work better; ISP's that plays wonderfully in online videogames are often very good for VoIP too.)
2. Good VoIP brand provider with good reliability. (i.e. CallVantage, Vonage, etc.) Sometimes one or the other works better with a particular ISP.
3. VoIP box or router with QoS as the FIRST box that connects to the Internet. (For example: Motorola VT2442). This makes sure that VoIP does not get interference if other people are downloading at the same time as your phone call.
4. Configure VoIP to maximum quality voice codec (G.711 digital codec). You have to do this to eliminate the scrambling in TTY.

I now have nearly flawless TTY transmission over this digital technology even while I am downloading stuff in the background -- no more scrambled text. There is sometimes a scramble during connection, or when the Internet is rarely slow. But still much better than if I was using an acoustic coupler in a noisy room.

Anyway, the reason why I use VoIP:
- I move often (I don't need to pay an installation charge when I move my phone line)
- It is cheaper (yes, sometimes it is not, BUT it is cheaper if you get the right VoIP account)
- I like voicemails/callerID being sent to me in an email (many VoIP services can send voicemails as an email). These show up on my pager.
- I do some computer programming, and am researching writing a software TTY softphone (22ms 1400/1800 FSK software codec in a SIP client -- please contact me at www.minitty.com if you can help me research this)

(Note: This is an advanced user procedure -- not for the faint of heart).
 
Hi there! Thanks for the information about getting TTY working with VoIP.

And yes I do have computer expertise so I don't seem to have any problem with that.

Thanks!
 
Hmmm...my edit post expired...

Well, since with a configuration of VoIP for compatibility with TTY, I think it would be great to receive TTY calls through mobile when someone dials my TTY number and I'm not home -- can't do that with My IP Relay because they can only accept voice calls even if they have TTY to call me.
 
Oh good grief thanks for the information. Yea I was having a hard time with mine in the past now that you made it all clear for me. Thanks :D
 
horselover61 said:
Oh good grief thanks for the information. Yea I was having a hard time with mine in the past now that you made it all clear for me. Thanks :D
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Anytime!

Most VoIP providers say they do not support TTY. My VoIP provider says it does not but it works anyway. You just have to have the right setup on a high quality internet connection (it's a lot to remember for somebody unfamiliar with VoIP)
 
I've already ordered Vonage Unlimited Plan and I am going to try it out with TTY.

Here's what I get from Vonage about the codec:

Dear Grayson Peddie,

Thank you for contacting Customer Care.

We understand that you have queries regarding functioning of TTY with
Vonage.

We would like to inform you that all of our devices support G711
codec and it is by default configured with our devices, which supports
maximum possible voice quality.
Click to expand...

While Vonage tells me to contact the TTY vender, I don't think it's necessary because I think it will work since I have my Ameriphone Q90-D TTY which includes a phone jack built-in.

With the VoIP support for TTY, I felt surprised that I would be able to test out Vonage with my TTY! Plus, it's much easier than my cell phone (Alltel Motorola V710) and eases my frustration. I tried to flip the analog/digital switch to analog but the switch broke and can't afford another $200 portable TTY machine. Well at least I have my RIM Blackberry 7290, but can only receive voice calls through relay and not TTY (I registered my "My IP-Relay.com phone number).
 
GraysonPeddie said:
I've already ordered Vonage Unlimited Plan and I am going to try it out with TTY.
Click to expand...

I've used Primus TalkBroadband and I've used Vonage. Both are TTY compatible assuming you are using a good high-speed ISP. (preferably a good "XBOX Live" compatible ISP)

Your weak link will probably be the ISP. Are you with a good ISP? -- speed of ISP is not as important as predictable latency of the ISP. Sometimes Cable Internet is usually worse than DSL (high speed telephone line) Internet because of latency problems, but it depends on the area and how overloaded your Internet service is. If your Internet consistently slows down during daytme, then that may be a bad sign for VoIP. (Good ISP's stay almost just as fast daytime and nighttime -- another sign of a good ISP). Also, I notice that occasionally there is one instance of scrambling at the beginning of a TTY conversation (initialization of a connection works funny), so press the spacebar a few times right after connecting. Then conversion is perfect for the rest of the call.

If you already have a router, you might want to ignore the instructions that come with your VoIP box (plug into an existing router port), and put the VoIP box as the first box of your Internet connection. It might work fine the other way, but downloading stuff on the Internet will start to scramble the TTY conversation if you do it this way.
 
Are you assuming that I didn't read the instructions in the first post in the thread? I've assumed myself that Comcast is XBox Live compatible. I didn't read your post that much except the first post of the thread and I already got the information.
 
sometimes I made a call and it doesnt come thru then have to call back again then it will come thru. Sometimes it is scramble and i had to hit the space bar or call back again. It is so frustrating. Now I am trying to figure out what the best way to contact my bf since he only use tty. He have no knowledge of computer or no vp. I will have to teach him to use the computer to talk to me online instead the phone cuz he is the only person that I talk on tty and no one else. So why waste my time with tty. Oh brother
 
Yaaaaaaaay! It worked! I am happy about the Vonage that I got and since I connect between the cable modem and router, it worked!!!

I called my mom via relay (can't do 711, since I get a blinky light and no text in my TTY) and the relay service seemed to receive text clearly and I can get clear text from the relay service without any problems!
 
About the G.711 codec Mark Rejhon mentioned, I'll post information found here:

ITU G.711

G.711 is a high bit rate (64 Kbps) ITU standard codec. It is the native language of the modern digital telephone network.

Although formally standardised in 1988, the G.711 PCM codec is the granddaddy of digital telephony. Invented by Bell Systems and introduced in the early 70's, the T1 digital trunk employed an 8-bit uncompressed Pulse Code Modulation encoding scheme with a sample rate of 8000 samples per second. This allowed for a (theoretical) maximum voice bandwith of 4000 Hz. A T1 trunk carries 24 digital PCM channels multiplexed together. The improved European E1 standard carries 30 channels.

There are two versions: A-law and U-law. U-law is indigenous to the T1 standard used in North America and Japan. The A-law is indigenous to the E1 standard used in the rest of the world. The difference is in the method the analog signal being sampled. In both schemes, the signal is not sampled linearly, but in a logarithmic fashion. A-law provides more dynamic range as opposed to U-law. The result is a less 'fuzzy' sound as sampling artifacts are better supressed.

Using G.711 for VoIP will give the best voice quality; since it uses no compression and it is the same codec used by the PSTN network and ISDN lines, it sound just like using a regular or ISDN phone. It also has the lowest latency (lag) because there is no need for compression, which costs processing power. The downside is that it takes more bandwidth then other codecs, up to 84 Kbps including all TCP/IP overhead. However, with increasing broadband bandwith, this should not be a problem.

G.711 is supported by most VoIP providers.
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