Lecture #5 covered some aspects of agent communication.
Two good papers on agent communication languages are:
T. Finin, Y. Labrou and J. Mayfield, KQML as an agent communication language, Proceedings of the 3rd International Conference on Information and Knowledge Management, Gaithersburg, Maryland, 456-463, 1994and
M. P. Singh, Agent Communication Languages: Rethinking the Principles. IEEE Computer, 31(12), December 1998, pages 40-47.