The ATTU needs to receive ZDA with PPS or UTC with PPS only. The ATTU will disregard the ZDA or UTC when received as a combination of strings such as ZDA and GGA (or any other NMEA strings) as processing the unwanted string can affect the timing.
In contrast to connecting to a GPS ZDA and PPS output, Internet NTP Time Servers can be quite difficult to connect to, even in an office setting. Gateways, Firewalls and such can affect the ATTUs ability to connect to a NTP server.
The ATTU requires the IP address of the NTP server. This can be found through the Command Prompt with the NSLOOKUP command. Use the computer that is connected to the ATTU to ensure that the NTP server is accessible at the location with a PING command.
