This Recommendation should be associated with [ITU-T H.221] and [ITU-T H.230]. A number of applications utilizing narrow-band (3 kHz) and wideband (7 kHz) speech together with video and/or data have been identified@ including high quality telephony@ audio and videoconferencing (with or without various kinds of telematic aids)@ audiographic conferencing@ and so on. More applications will undoubtedly emerge in the future. To provide these services@ a scheme is recommended in which a channel accommodates speech@ and optionally video and/or data at several rates@ in a number of different modes. Signalling procedures are required to establish a compatible mode upon call set-up@ to switch between modes during a call and to allow for call transfer. Some services will require only a single channel which could@ according to the procedures in this Recommendation@ be B (64 kbit/s)@ H0 (384 kbit/s)@ H11 (1536 kbit/s) or H12 (1920 kbit/s). Other services will require the establishment of two or more connections providing B or H0 channels: in such cases the first established is called hereafter the initial channel while the others are called additional channels. Unless otherwise specified@ all references to frame alignment signal (FAS) bit-rate allocation signal (BAS) and service channel (SC) refer to the initial channel or@ in the case of a higher-order channel@ to the time-slot No. 1 of this channel. All audio and audiovisual terminals using G.722 audio coding and/or G.711 speech coding or other standardized audio codings at lower bit rates should be compatible to permit connection between any two terminals. This implies that a common mode of operation has to be established for the call. The initial mode might be the only one used during a call or@ alternatively@ switching to another mode can occur as needed depending on the capabilities of the terminals. Thus@ for these terminals@ an in-channel procedure for dynamic mode switching is required. The following clauses develop these considerations and describe recommended in-channel procedures.