I. INTRODUCTION II. COMMUNICATION HIERARCHY FOR SIGNALING IN CELL BIOLOGY III. LEVEL 1 - PHYSICAL SIGNAL PROPAGATION IV. LEVEL 2 - PHYSICAL AND CHEMICAL SIGNAL INTERACTION V. LEVEL 3 - PHYSICAL/DATA INTERFACE VI. LEVEL 4 - LOCAL DATA ABSTRACTION VII. LEVEL 5 - APPLICATIONS VIII. END-TO-END CASE STUDIES IX. OPEN PROBLEMS X. CONCLUSION