 (with an RJ- 45) and a 50-Ohm signal (for coaxial cable of less than 3 m length). There are additional details for the 100-Ohm V.11 version in Annex A of ITU-T G.8271. The connectors for the 50-Ohm version are not specified, but as with 10 MHz, BNC connectors are typically used on the PRTC side. For similar reasons to the 10-MHz case, the connector on the equipment connected to the PRTC can vary considerably. For example, as was shown in Figure 3- 18, most Cisco routers have the DIN 1.0/2.3 connector for 1PPS as well as 10 MHz, but several other connectors are used by other companies and industries. The 1PPS connector has a very important function as a measurement interface, meaning that it al- lows a quick method of checking the phase offset of a device compared to some source of phase. Figure 3-19 shows how the 1PPS port is used to measure phase alignment. PRTC + T-GM Timing network Slave 1PPS out 1PPS out Tester Figure 3-19 Using 1PPS as a Measurement Port Obviously, in this case, the devices must be close to each other because of the distance limitations of the 1PPS signal. Field test personnel use an alternative approach when testing equipment in re- mote locations. They use a portable tester with its own built-in GNSS receiver, SO that the test device can recover the phase from the GNSS radio signal and compare the offset to the pulse on the cable from the 1PPS output port. This is an important function and one reason why many timing-aware devices have 1PPS output capability as well as the ability to accept 1PPS input. Remember that the 1PPS signal is not used in TDM (SONET/SDH) networks or in SyncE, because they are both only concerned with frequency. Time of Day The ToD signal is made up of a string of characters that encodes the time in a manner that allows the receiving device to reconstruct UTC. So, while 10 MHz delivers frequency and 1PPS indicates the instant when the second commences, the ToD says what is the actual second that has just started. This signal often uses ITU-T V.11 (RS-422) or somethi