The current Internet is built on a set of protocols, but exhibits problems in supporting applications. The network is optimised for best-effort traffic, but other functional aspects are widely neglected. Applying concepts well-known in software engineering (abstraction, composition, separation of concerns) to design the future Internet architecture is seen as a promising way forward. This paper presents a case study using Model Driven Development addressing interoperability requirements in next generation networks. Our approach focuses on the specification of a high level Contract Domain Specific Language we combine Component-based Software Engineering for the design with our long-term experience of network resource management and performance optimisation. Part of our case study is a tool chain that supports the network engineers who deploy next generation networks.