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Mobile geographic services
Telephone protocols Throughout the world a number of different low-level telephony standards are available. The current first generation of analog mobile telephony systems were designed for voice and are poorly suited to data transfer. The Global System for Mobile Communications (GSM) adopted in many parts of the world (note, however, that the US system is different than that used in Asia and Europe) offers a maximum data transfer rate of less than 10 Kbps (Kilobits per second) today. Newer second generation (2G) systems becoming available now, such as the General Packet Radio Service (GPRS), Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA) can provide data transfer at up to about 40 Kbps. Upgrades to 2G systems, called 2.5G, promise +100 Kbps, but these will not be available until the end of 2001 in Europe and possibly even later in the US.  Fig. 4: A mobile geographic service based on ArcPad and ArcIMS In the last few years there has been enormous hype associated with WAP (Wireless Access Protocol). The WAP specification encompasses a relative simple and compact version of XML (extended markup language) called WML (Wireless Markup Language) suitable for issuing requests to servers and returning results. WAP also supports the inclusion of wireless bitmap (WBMP) files. Thus it is possible to make requests to a geographic service from a WAP phone and return the results as display page (called a card) containing a map in the form of an embedded bitmap. As the hardware capabilities of client devices continues to improve, software applications become more advanced, and bandwidth limitations are alleviated, greater interest will focus on using the more widely accepted HTML and XML protocols. HTML is concerned with data presentation, whereas the more extensive XML supports data content description and structuring.  Fig. 5: San Diego Real-time traffic. Small, hand-held client device Advancements in hardware performance have allowed the development of small, low-powered, devices suitable for mobile geographic applications. The current situation is characterized by great diversity with higher end systems offering a quarter VGA screen (320 by 240 pixels), 8-bit color (64 colors), 32 MB of RAM and a 200MHz or more processor. The choice of operating systems includes Windows CE, Palm OS, EPOC, JavaOS and Linux. Some examples of devices include.
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