26.2263GPPCellular text telephone modemGeneral descriptionRelease 17TS
Deaf, hard of hearing, and speech-impaired persons have been using specific Text Telephone (referred to as TTY in North America) equipment in the fixed network for many years to transmit text and speech through ordinary speech traffic channels. Modern digital cellular systems, however, do not provide satisfactory character error rates for text transmitted in the speech channel with the traditional modulation developed for the fixed network. The FCC under the US Government has required an urgent solution for all emergency (911) calls for one specific text telephone protocol called Baudot Code. This TS addresses these FCC requirements, and specifies a solution for the GSM and UMTS and potentially other cellular technologies. The goal is to provide a solution that can support all traditional text telephony systems worldwide. Internationally, PSTN text telephony is standardized in ITU-T V.18  and ITU-T T.140 .