Streaming Media to Mobile Audiences
If you were buried under projects this past year and not paying attention to the industry, you might have missed the fact that streaming media is finally reaching beyond PCs and set top boxes to mobile hand sets. In 2004, mobile phone service subscribers around the world are signing up for and experimenting with new, enhanced services featuring synchronized audio and video. The first mobile rich media application to launch is video messaging, since it is a straightforward evolution of photo messaging and immediately appeals to target audiences' need to communicate personal information. Access to streaming media archives of news and sports content is also compelling to many mobile phone users.
The evolution of mobile streaming media services is a direct function of what network operators call "generations" of technology. First generation (1G) mobile networks (through the 1980s) were analog, designed to carry voice and voice-call signaling. Unlike the Internet, which is fundamentally a shared resource, their architecture was circuit-switched (like the traditional public fixed-line telephone network); for the duration of a call, two parties are the exclusive users of their particular connection (or "call path") through the network. When their call is completed and they hang up, the call path is torn down and the network resources (e.g. connections and switch ports) can be re-assigned to the next users. The second generation (2G) mobile networks deployed in the 1990s are digital but still circuit switched and began only carrying voice and voice-call signaling. Eventually data services were deployed over 2G networks, but using circuit-switched data paths at bit-rates of 14.4kbps—much like early modems over the traditional fixed line telephone networks. Given the low data communications bandwidth and circuit-switched architecture of 2G networks, video streaming to mobile phones had trouble getting off the ground. For the same reasons, other less demanding forms of data communications (e.g. Internet access, email, or data downloads) also languished behind mobile network operators' targets.
Between 1998 and 2002, as the demand for all kinds of data communications over mobile phones and mobile PCMCIA cards grew, operators upgraded their networks to two-and-half generation (2.5G) technology. These networks move data communications off the circuit-switched side of the network to a purely IP-based data platform that uses technology similar to (and integrates nicely with) the Internet. The increased bandwidth and new application flexibility offered on the new platform create opportunities for developers of streaming media systems to leverage their core technologies to enable what we see emerging today.
The dominant 2.5G network technology is GSM-GPRS (Global System for Mobile communications-General Packet Radio Service). GPRS is theoretically capable of just over 100kpbs, but more realistically delivers a consistent overall average of 30kbps. Even faster 3G networks (theoretically promising 384Kbps to 1Mbps) are already being built and some 3G services have been launched. But 2.5G is proving to be more than adequate to get mobile video streaming and messaging into the market, largely using extensions of current Internet streaming media technology.
In contrast with content prepared for PC monitors, the content streamed to mobile users is much smaller. Screen sizes vary from 128 x 160 pixels to 208 x 320 pixels and color depth varies from 12-bit (4096 colors) to 16-bit (over 65,000 colors), depending on the handset manufacturer and model. Over GSM-GPRS mobile networks, streams start playing five to 10 seconds after the mobile user’s click and frame rates range from four to eight frames per second.