NSA/CSS Secure Telephone System

Overview
The NSA/CSS Secure Telephone System (NSTS''') is the NSA's internal telephone network for calls up to the level of Top Secret/SCI. Newer NSTS phones are connected by fiber optic modems to a fiber backplane that interfaces with an NSANet access point router. The voice traffic is then encrypted together with data traffic utilizing a Type 1 bulk encryption device.