er IP, SIP signalling, WWW and e-mail. ROHC is included in 3GPP specifications from release 4. It is defined in TS 25.323, Packet Data Convergence Protocol (PDCP) specification. ROHC is also included in 3GPP2 (CDMA2000). Combinations of these tools are used to get the most economical transmission to fulfil the service requirements. 5.7.1 3GPP MEDIA CODECS Every media codec developed and standardized in, or adopted by, the 3GPP is suitable for use in wireless applications. Important factors affecting codecs are bit rates, complexity Understanding Changing Telecommunications - Building a Successful Telecom Business IPv6 header (40) IPv6 header (40) IPv6 header 60 UDP header (8) UDP header (8) RTP header (12) RTP header (12) Speech payload Speech payload (32 octets) (32 octets) Compressor Decompressor Average header size close to 1 bit Compressed header (1-6) Compressed VolP packet Speech payload (32 octets) Figure 5.12 Example of header compression from 60 bits down to about 1 bit. ROHC opera- tions - VoIP example (in terms of millions of instructions per second, MIPS), memory (in terms of RAM and ROM), quality in error-free conditions and in typical wireless environments, and cost of implementation. A number of standardized media types for text, voice, audio, images and video are listed below: XHTML basic: XHTML Basic is designed for web clients that do not support the full set of XHTML features, for example mobile phones, PDAs, pagers and set-top boxes. AMR: the AMR voice codec (3GPP TS 26.090) encodes narrow-band (4 kHz 'telephony' bandwidth) voice using one out of eight rates between 4.75 kbit/s and 12.2 kbit/s. The media type is well suited to all voice and news clips. AMR was standardized by ETSI in 1998. AMR will be further described in Chapter 8. AMR wideband: the AMR wideband voice codec (3GPP TS 26.190) encodes wideband (8 kHz audio bandwidth) signals using one out of nine rates between 6.60 kbit/s and 23.85 kbit/s. The media type is well suited to all kinds of voice and audio clips, and provides high-qua