To help understand the message envelope parameters, consider the analogy of a bill collection agency that collects for several utilities. When sending a bill, the agency must specify:

1. The person receiving the bill (more specifically, their ID number). This is the destination.
2. What month the bill covers. Since the person will get twelve bills each year, they need to know which month this bill covers. This is the tag.
3. Which utility is being collected for. The person needs to know whether this is their electric or phone bill. This is the communicator.