Frank-Uwe Andersen, Cornelia Kappler (Siemens AG)
Hermann de Meer, Ivan Dedinski, Jens O. Oberender (Universität Passau)
Andreas Mäder, Kurt Tutschku (Universität Würzburg)
Abstract:P2P file sharing systems account for a high percentage of traffic volume in the fixed Internet, having exceeded http (www) or email traffic. P2P file sharing may also be an interesting application in mobile data networks such as 2.5/3G. In particular in cellular mobile environments, operation of P2P systems encounters several problems, such as a relatively narrow and expensive air interface, highly varying online-state (presence) of subscribers, hierarchical network structure, and limited device capabilities. The desire of operators is to add some value to P2P data flows and to turn them into services. At least some control over traffic and content should be possible, while preserving the basic P2P user experience and connectivity. Operation of P2P file sharing services in next generation mobile networks has to suit the needs of users as well as to accommodate the constraints imposed by 3G mobile technology and 3G network operation.
The two main restrictions of the air interface, a relative low effective bandwidth and high latencies, make it essential to reduce the signalling overhead as much as possible to achieve acceptable performance. Traffic between peers, i.e. signalling and download should be limited, since all mobile-to-mobile transmissions use twice the amount of air interface resources compare to mobile-to-fixed-network transmissions. Signalling between peers should be limited, since on packet transmission utilizes twice the air interface. P2P applications have to maintain the autonomy of users, i.e. users retain the ability to decide what resources are shared and how this is accomplished. Since resources are provided locally, in a decentralized manner, the control on the resource access should be implemented also in a decentralized way. Because mediation performance dominates the user experience with the P2P system, it is a essential success factor to its popularity. We investigate the possibilities of defining a mobile P2P architecture where the decentralized operation of P2P file sharing can be reconciled with the interests of network operators.
One of the most important requirements of mobile network operators is to maintain control over the network and to charge for provided services. If mobile P2P is integrated into the service structure, it is therefore required to provide means for controlling and for charging. The control mechanisms for a mobile P2P system must be carefully designed in order to avoid the total degeneration towards a centralized system. Control mechanisms should not tamper fundamental P2P concepts such as decentralization. An initial step in the design of a mobile P2P architecture is to find out on how current control or transport mechanisms of GSM/GPRS and UMTS can be used for providing mobile P2P services. The mechanisms are classified and evaluated according to the nature and degree of their control concept.