There is disclosed methods, apparatus, and computer programs relating to a Software Defined Network (SDN) for use in a communication network. The SDN acts as an entity in a first service chain of entities through which a data flow is routable by another SDN in the communication network. The first service chain comprises one or more service applications each for performing a service on data from the data flow at a logical layer in the communication network associated with that service application. The SDN routes data from the data flow received at the SDN through a second service chain comprising one or more SDN service applications. An SDN service application of the second service chain is for performing a service on data from the data flow at a higher logical layer within the communication network than is a service application of the first service chain.