Text over IP (ToIP)
Text over IP (ToIP), also known as Real-Time Text (RTT), is a means of sending text in real-time over IP network within the context of a multimedia session.
This technology was originally designed to meet the needs of the deaf and hard-of-hearing users who rely on text communication as a part of normal daily communication. The idea originated with legacy telephony devices that had an accoustic coupler that would allow a user to send text over PSTN networks using one of several protocols like Baudot.
Resources: VoIP Information Site, RFC 4103, TTY Basics
See Also: Voice over IP (VoIP), IP Telephony (IPTel)