1. Introduction

   There are multiple IETF protocols for establishment and termination
   of media sessions (SIP [6]), low-level media control (Media Gateway
   Control Protocol (MGCP) [7] and Media Gateway Controller (MEGACO)
   [8]), and media record and playback (RTSP [9]).  This document
   focuses on requirements for one or more protocols to support the
   control of network elements that perform Automated Speech Recognition
   (ASR), speaker identification or verification (SI/SV), and rendering
   text into audio, also known as Text-to-Speech (TTS).  Many multimedia
   applications can benefit from having automatic speech recognition
   (ASR) and text-to-speech (TTS) processing available as a distributed,
   network resource.  This requirements document limits its focus to the
   distributed control of ASR, SI/SV, and TTS servers.

   There is a broad range of systems that can benefit from a unified
   approach to control of TTS, ASR, and SI/SV.  These include
   environments such as Voice over IP (VoIP) gateways to the Public
   Switched Telephone Network (PSTN), IP telephones, media servers, and
   wireless mobile devices that obtain speech services via servers on
   the network.

   To date, there are a number of proprietary ASR and TTS APIs, as well
   as two IETF documents that address this problem [13], [14].  However,
   there are serious deficiencies to the existing documents.  In
   particular, they mix the semantics of existing protocols yet are
   close enough to other protocols as to be confusing to the
   implementer.

   This document sets forth requirements for protocols to support
   distributed speech processing of audio streams.  For simplicity, and
   to remove confusion with existing protocol proposals, this document
   presents the requirements as being for a "framework" that addresses
   the distributed control of speech resources.  It refers to such a
   framework as "SPEECHSC", for Speech Services Control.

1.1. Document Conventions

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [3].