TIA/EIA TSB 121

Description / Abstract: INTRODUCTION

This Telecommunications Systems Bulletin (TSB) describes a possible implementation of the interface between a mobile station and a TTY. Recognizing that:

• FCC Rule and Order CC Docket No. 94-102 "E9-1-1/TTY Compatibility" requires wireless service providers to support TTY compatibility for contacting assistance in an emergency.

• The CTIA/PCIA TTY Forum requested that TIA TR-45 specify a 2.5mm connection with appropriate electrical parameters which would allow reliable audio interconnection between TTYs and mobile wireless handsets.

• The majority of legacy TTY terminals only support audio connection to the telephone network via: (See Section 6.: Interconnect Options)

- Acoustic coupling utilizing the wire-line handset placed into flexible cups designed for Type G or Type K handsets. .

- FCC Type RJ-11 modular connection.

• Due to the wide variety of shapes and sizes of modern wireless handsets, neither of these modes of connection are applicable to mobile wireless handsets.

• TIA/EIA/IS-789-A describes electrical specifications to adapt wireless handsets to a vehicular environment.

This TSB specifies an interface that will support direct audio connections between TTYs and mobile wireless handsets based upon TIA/EIA/IS-789-A.