This annex introduces the notion of Simple Endpoint Types (SETs) that are designed to operate in well-defined set scenarios and with a restricted functionality range - in contrast to full-fashioned H.323 multimedia systems - thereby explicitly reducing the overall system and hence the implementation complexity. In particular, this annex defines Simple Endpoint Types for audio communication (Audio SETs) that operate using a well-defined subset of H.323 protocols and are well-suited for IP Telephony applications while retaining interoperability with regular H.323 (1998) devices. NOTE - The subset of H.323 defined in this annex is derived from the specific requirements for Audio SETs and also documents current practice as observed in the market place and at interoperability events.