Figure 4.
The left-hand side image shows an architecture of a single transition down (TD) unit, while the right-hand side image shows the architecture of a transition up (TU) unit.
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.