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Using a TTY maching and TRS with VoIP

Teletypewriter (TTY) machines are typewriter-style devices used by the hearing-impaired community to communicate over the phone. A TTY machine can work with VoIP, and the Telecommunications Relay Service (TRS), a free service that connects customers who are deaf, hard of hearing, or have speech disabilities with others using either standard phone equipment or phone equipment that has been specifically designed for individuals with disabilities.


Here are some things you’re going to want to check to help ensure that your TTY machine and TRS can work correctly with VoIP.

To use TTY/TRS with VoIP:

  • Set your TTY machine to the G.711 codec. G.711 is also known as pulse code modulation (PCM) and compresses data to enable faster transmission and decompresses received data.

  • Access TRS by dialing 711 or by using the toll-free TRS number listed in your phone book.

    Relay service is available 24/7/365. A trained communications assistant answers your call and relays the conversation between you and the person you called. All call information and conversations are confidential. Long-distance calls can be billed collect or to a prepaid calling card, carrier calling card, or third party.

  • To make an emergency call using TTY:

    1. Dial 911 directly (or other existing emergency numbers).

    2. When the 911 dispatcher answers the call, press the space bar to let the dispatcher know that the call is a TTY call.

Caution: You can call 911 using TRS, but there may be a delay in reaching emergency services.