Multi-Cost ALTO

IETF is designing a new service called ALTO (Application Layer traffic Optimization) that includes a "Network Map Service", an "Endpoint Cost Service" and an "Endpoint (EP) Ranking Service" and thus incentives for application clients to connect to ISP preferred Endpoints. These services provide a view of the Network Provider (NP) topology to overlay clients. The present draft proposes a simple way to extend the information provided by the current ALTO protocol in two ways. First, including information on multiple Cost Types in a single ALTO transaction provides a better mapping of the Selected Endpoints to needs of the growing diversity of Content and Resources Networking Applications and to the network conditions. Second, one ALTO query and response exchange on N Cost Types is faster and more efficient than N single cost transactions. All this also helps producing a faster and more robust choice when multiple Endpoints need to be selected. Last, the draft proposes to enrich the filtering capabilities by allowing constraints involving several metrics combined by several types of logical operators. This allows the applications to set finer requirements and above all to include compromises on those requirements.