Explicit application-network cross-layer optimisation

The emergence of overlay network applications that rely on application-level decisions for many aspects of their operations (e.g. routing, content replication, etc) creates cross- layer interaction issues with ISP network operations. Indeed, the independent optimisation of a diverse set of objectives using layer-local information can lead to operational instability and sub-optimal resource usage. We argue that an explicit interaction between the application and network layers can provide benefits for each layer. We postulate that such cross-layer interaction must however fulfil two conditions to be pragmatic and acceptable: 1) no explicit information about the structure and operations of each layer must be ex-changed; 2) each layer must be able to independently set its own policies and objectives. Because we limit this interaction to application hosts and their access ISP, the proposed method is also incrementally deployable. We show, through evaluation of simple examples, that explicit cross-layer interaction does indeed bring performance benefits to all parties, for applications ranging from simple client-server to more complex overlay network scenarios.