This paper investigates the problem of interoperability of ECUs in a distributed control system consisting of a set of ECUs connected by a serial communication channel. If the application tasks executing within an ECU depend on the temporal properties of the data delivered by the communicatioin channel, then a precise specification of the temporal interface properties is a prerequisite for interoperability. Such a precise interface specification can be developed if the communication system is time-triggered and the points in time, when the information is updated at the receivers, is known a priori. In the second part of the paper the concept of a “temporal firewall” is introduced to precisely specify the input and output interfaces of a node in the value domain and the time domain. Examples for temporal firewalls in a distributed vehicle control system are given.