Chapter 2: Trends Towards Mobility 37 Do the data rates in wireless links really matter? Yes – in a big way. The data throughput capacity of a wireless network (or any data link, in fact) directly dictates how much content it can pump to and from mobile devices. That, in turn, heavily affects the usability of the network. This may not matter for small fi les such as brief e-mail messages, but becomes crucial with larger fi les, such as video. People may be pre- pared to wait for a few seconds to receive an MP3 song, but waiting a day to download a feature movie from YouTube (see section 7.3 on 21 video sharing) is not practical with wireless devices yet. A typical Bluetooth transceiver found in many mobile phones has a practical data rate in the order of 500 kbit/s. This means that it takes a minute or two to beam an MP3 song from one phone to another. This is a wait many people tolerate. However, copying a DivX movie of 500 MB this way could take hours. For faster data rates, clever college students would probably hook up phones via USB into PCs, or simply swap memory cards. The channel capacity has, we repeat, a major effect in the usability of media over that channel. Given the various access technologies both in the long and short range, with different capacities and costs, it is not straightforward to decide which channel to use. The notion “any content, anywhere, anytime” is simply not realistic at the moment – and may never be, as long as the communication channels differ in a way that affects the users’ convenience or their budgets. Speed does not come for free, either. It always costs energy to transmit bits, and the faster you send bits, the faster you run out of juice. For larger data transfers, small media devices may need backup power. As a consequence, wireless users need to become somewhat aware of such parameters as transmission times, power consumption, and costs. This is a huge challenge, considering that it is the general public that we are talking about! Moreover, the application designs must take the various channels into account. Even more fundamen- tally, the variety in access methods has an effect on the design of the content formats and content architectures. Consider the case of a large, high-quality MP3 collection, which might be, say, 200 gigabytes. It is not practical today to fi t that collec- tion into an MP3 player. However, the player could still easily contain the ID3 tags of all those songs and albums. The metadata (see Chapter 21 Will wireless communications become the norm? Is the time at hand when we can break loose of the tangled wires? Sorry, not quite. Wired communications is always faster than wireless by, say, two or three orders of magnitude. When WLAN gets to 500 Mbit/s, the wired Ethernet will already be doing hundreds of gigabits per second. We may be eternally fated to balance between wired speed and wireless freedom.