 system. Transfer of high quality pictures can for example be solved either by high bandwidth (bits/s) or by using efficient codecs with compression algorithms (see Figure 5.12). More- over, if the user data is not transferred in conversational or streaming modes, time is a third parameter to play with. WAP provides faster communication through compressed and encoded data and headers. A very efficient header compression is offered by the standard robust header compression Services Examples of traffic situations FTP traffic 634 Mbps SMTP traffic 30 Kbps FTP traffic 8 Mbps HTTP traffic 45 Kbps Figure 5.10 A content-based view 1. Voice (fixed PSTN developing towards cellular PLMN) 2. Dialled up Internet 3. Broadband Internet 'Always on', etc. Figure 5.11 Driving applications in the fixed network (ROHC). See Figure 5.12. The ROHC can be used for services such as VoIP, video over 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 typi