l on a pair of pins output from an RJ-48c port. Operators can configure their nodes to produce both these signals for output, which would allow an engineer to quickly test the synchronization situation on that network element. Obviously, for this to work, the equipment needs to support some way to output these signals, but some types of equip- ment may not. For example, it is unlikely that a mobile radio has a 1PPS output jack that can be used to measure phase/time error. In that case, the only alternative available might be to test the next-to-last router in the chain to see how good the TE is immediately before the last hop. Another (developing) alternat- ive would be to test the time alignment of the radio signal itself-in what is often called over the air testing. It is also possible to use SyncE to measure frequency and PTP to measure the phase. However, there are negat- ive security and operational complications if you do that. No operator wants to leave equipment on remote loc- ations with active Ethernet ports ready for a test because of the risk to security. The alternative is that the field engineer must coordinate with the network operations to have them configure a test port whenever a field test is scheduled and close it afterwards. So, if measurement ports are available on the DUT, the next requirement is a piece of test equip- ment that has a frequency and phase reference to measure the DUT signals. One piece of equipment that the authors commonly encounter for this role is the Sentinel from Calnex Solutions. Figure 12- 24 illustrates one of those test devices-as you can see, it is designed to be handy and portable. Figure 12-24 Sentinel Field Tester from Calnex Solutions These devices allow the connection of frequency sources (such as SyncE, E1/T1, 2048 kHz, 10 MHz) and phase signals (1PPS, PTP) to enable time error and frequency measurements. See the preceding sections on testing networks for frequency wander and phase alignment for details on the specifics of these tests. The next issue is to fi