the phase alignment. To not make this section overly complex with repetitions of the same message on the T-TSC com- pared to the T-BC, these differences are mentioned here at the start. However, understand that these differences apply throughout the rest of the following sections where they discuss methods for T-BC and T-TSC testing together. Remember also that before these test measurements (particularly hold- over) start, some time is needed for the DUT to lock to the signal, and additional time is needed for the clock to settle. Many operators no longer need a 1PPS signal to synchronize a piece of equipment, SO there is little point in measuring it, and PTP is preferred. The only scenario in which 1PPS testing might make sense is when operators want to use it as a measurement port. This is where a mobile engineer with a field tester goes to the remote device, plugs a special tester into the 1PPS port, and immedi- ately gets a readout of the phase alignment (see the section "Troubleshooting and Field Testing" later in the chapter). Of course, to validate this approach, the operator should ensure that the 1PPS is an accurate repres- entation of the phase on the device. For that reason, it makes sense to confirm that the 1PPS signal is closely aligned with the phase carried by the PTP signal. Most testers allow both the PTP and 1PPS TE from the DUT to be measured simultaneously. One additional method of testing these sorts of clocks is to use a tester that is capable of passively monitoring the PTP signals. For this topology, the testers receive a copy of the PTP messages and perform measurements on them. This might be better suited to a scenario where the DUT does not support the ability to have measurement ports or where the clock is distributed across multiple devices (such as a microwave system acting as a Telecom Transparent Clock [T-TC]). Further in- formation on testing a T-BC made up of two separate devices is provided later in the chapter in the section "Testing (Cascaded) Media Converters." There is som