QOS in mobile computing

Although there are already many fixed networked computers around the world, we will see several orders of magnitude more wireless and mobile devices connected to the Internet in the future. Each car, truck, aircraft, but also many people will carry a plethora of different devices for computing and communication. However, all mobile and wireless systems have in common that the quality of their connectivity may change rapidly over time. Still, users want to get the best quality possible or the quality they pay for respectively. Furthermore, people want to use well-known services and applications from fixed networks.Mobility is a key characteristic of today's society as also the tremendous growth rates in mobile communication systems show. Already today over 500, million people use mobile technology, far more than the (still mostly fixed) Internet. History shows that there is not one single networking technology covering all aspects of communication, the future will bring even more technologies. Examples are broadband infrastructures based on ATM or IP over Sonet, LANs based on Ethernet, wireless LANs according to IEEE 802.11, infrared access, mobile and cordless phone systems.New technologies include Personal Area Networks using, e.g., Bluetooth [1], scalable QoS provisioning in the Internet with Differentiated Services, and advanced protocol stacks for wireless and mobile communication (e.g., Wireless Application Protocol, WAP [2]). A single technology can never cover all aspects of communication. While in wired communication we could think of an ideal world with fiber to the desktop and powerful communication systems, the wireless and mobile domain puts several limitations on communication systems. Portability of devices restricts the performance, mobility imposes new requirements on QoS support, and wireless access limits the bandwidth. Particularly in mobile and wireless environments, several network technologies coexist, such as IrDA (Infrared Data Association), DECT (Digital Enhanced Cordless Telecommunications), GSM (Global System for Mobile communications), DAB (Digital Audio Broadcasting), or wireless LANs (e.g., IEEE 802.11) [3, 4].Depending on the current location, the user or mobile device can choose one (or more) of the available transmission links for communication with other mobile devices or for getting connected to the Internet. However, when looking at Quality of Service (QoS) one should keep in mind that in the end only the QoS perceived by a user really matters. While evolving at high speed, mobile computing and communication systems still suffer from low bandwidth, low performance due to battery limitations, but also consistency problems of distributed applications or security problems.First steps towards higher overall performance and thus higher QoS for users can be recognized: future mobile systems will not only have higher bandwidth (e.g., within the ITU IMT-2000 program [5]), but they will also combine different wireless technologies, such as high performance local wireless networks and wide area networks to offer good coverage and high bandwidth at certain hot spots. As it is currently happening for fixed networks, we will also see a strong convergence of telephone and Internet technology in wireless networks [6, 7, 8]. All third generation systems combine IP-traffic with traditional voice traffic [9].Furthermore, gateways to inter-connect telephone signaling with Internet signaling protocols are being developed. Still a big problem is the use of distributed applications that nowadays often assume permanent connectivity. In this case, the use of special middleware proxies and the extension of the widespread standard CORBA can offer a solution. Finally, no mobile and wireless scenarion can be developed without security in mind. While several architectures already offer partial security solutions, a common framework is still missing