Cross-Layer Protocol Design for Mobile Phones
The use of mobile phones is shifting its focus from voice-only applications to multimedia streaming, Internet browsing, file downloading, etc. The network protocols use the layered structure known from the open systems interconnection (OSI) model. This layered structure facilitates development of protocol components by abstraction such that a particular layer only has to concern itself with the interfaces to the layer above it and the layer below it. It also means that a particular layer only has to communicate with the corresponding layer at the other end of the link/network.
The existing layered network protocols were mainly developed for cabled networks and work very well with these. However, the wireless medium has very different properties in terms of for example channel fading and interference. We expect that cross-layer design will provide several benefits in optimization of network protocols for wireless access. Cross-layer design is an important part in relation to flexibility and adaptivity of the network protocol stack.
Cross-layer design is a means by which one can get specific knowledge across the protocol stack between separate layers. Cross-layer design allows exploiting flexibility in the protocol stack by using it to enable adaptivity - controlling specific features jointly across multiple protocols and layers. Cross-layer design extends the layered protocol by alteration of interfaces compared to the traditional architecture and it extends the architecture by communicating between non-adjacent layers. From a layered architecture point of view, cross-layer means enabling new interactions between non-adjacent layers and exchanging information and control between layers that was not possible in the original architecture. This makes it possible to optimize the operation of the protocol stack in a joint manner taking aspects of multiple layers into account.