tes of encoded representation. In the example in Figure 5.13, the WAP client (roaming MS) communicates with two web servers via GPRS. The WAP proxy gateway translates WAP requests to WWW requests thereby allowing the WAP client to submit requests to the web server. The proxy also encodes the responses from the web server into the compact binary format understood by the client. If the web server provides WAP content (e.g. WML), the WAP proxy retrieves it directly from the web server. However, if the web server provides WWW content (such as HTML), a filter is used to translate the WWW content into WAP content. For example, the HTML filter would translate HTML into WML. 5.7.3 SUMMARY OF BANDWIDTH SAVING METHODS See Figure 5.14. 5.8 BANDWIDTH REQUIREMENTS In line with what has been said above, services may need a large span of bandwidths on the transmission line. See Figure 5.15, which shows a large area for streaming and download services. Some further indications may be of interest. The following list is collected from a number of sources (even if is delicate to indicate figures at all when the range is SO wide): Services Bandwidth saving examples AMR voice H.263 video Codec Codec Session signal www HTML WTP/WDP + adaptation Traffic classification, channel setup Header compression RFC 2507 TCP/IP PDCP (packet data convergence Link layer Transparent PDCP Non-transparent PDCP protocol) provides control MAC layer Speech channel Video channel Un-reliable data channel Reliable data channel information compression Physical layer Figure 5.14 Summary of bandwidth-saving methods Quality range Streaming delivery Sports events Surveillance Download delivery Music video Movie clips News (video with voice) Music listening Slideshow (images with voice) Animated advertisements Voice/audio with text or images Bit rate kbit/s File size kBytes/30s Figure 5.15 Bit rate demands and storage requirements for on-demand mobile services Conversational voice services including IP telephony at around 10 kbit/s. Conversational video telephony