In this paper, the authors introduce a Domain-Specific modeling Language (DSL) for modeling application-level network protocols. Application-level messages may be expressed in object-oriented general-purpose programming languages as classes. Instances of these classes can be sent through the network with the help of a customized serialization process. However, protocols have several special characteristics that do not fit easily into this abstraction, for example, bitfields or specially encoded lists. Furthermore, the limitations of generic serialization frame-works inhibit using them for this purpose.