|  |  | The fielded sensors and the director communicate to each other through the post office. Even services on the same host communicate with each other through the post office. All communication is based on three identifiers: organization, host, and application. Through these identifiers, devices can identify each other at a more in-depth level than IP address. The identifiers can be layered on top of existing network protocols to ensure interoperability. This allows for fault tolerant connectivity across heterogeneous network architectures, addressing a larger domain than IPV4.