Virtual networks in the cellular domain
Abstract: Data connectivity between cellular devices can be achieved in different ways. It is possible to enable full IPconnectivity in the cellular networks. However this connectivity is combined with a lot of issues such as security problems and the IPv4 address space being depleted. As a result of this many operators use Network Address Translation in their packet data networks, preventing users in different networks from being able to contact each other. Even if a transition to IPv6 takes place and the potential problem of address space is solved, it is not likely that operators will leave their packet data networks open to the Internet. An alternative to solving the problem on the IP level is to use overlay networks. In an overlay network applications on the cellular devices identify themselves at the application level rather than on the IP level. While full IP connectivity always gives the most efficient routing, an overlay network can offer services that are difficult to implement on the IP level. This can enable an application to span Network Address Translating entities without having to share the entire device. They can also provide private dynamic virtual networks and groups for users that trust each other. These private networks can use permissions and group casting functions, without the problems associated with traditional IP multicast. The relatively limited bandwidths of the GSM and UMTS networks allow for application level routing of continuous data streams if the overlay network is distributed enough and mapped to the physical network in an efficient way. One of the advantages of using overlay networks is that although standard IP networks may be able to offer similar services in the future, overlay networks can be implemented in the existing IPv4 networks today at comparatively low costs. This may create the incentive needed in order for future larger investments to be justified. A distributed overlay network not only allows for real-time services such as instant messaging, which is already possible with a centralized server solution, but it also allows for higher bandwidth services such as video conferencing, Voice over IP, etc. that are not possible on a large scale with a centralized relaying server. An overlay network could be implemented by any third party without the support of an operator. This suggests that free networks may be created for what could be called reversed file sharing, i.e. networks where users upload files to each other rather than download as in most existing file sharing networks. These could become direct competitors to SMS, MMS and other operator-owned services. The thesis investigates the mentioned possibilities and potential threats. Along with this an implementation of an overlay network for cellular devices is created that is totally independent of the operator’s network.
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