s depending on the test case being executed. There are also physical ports on the rear for 1PPS and 10-MHz reference signals (see following section, "Ref- erence Signals and Calibration") as well as measurement ports for TDM signals like E1 and 2048 One important consideration is to ensure that the equipment is rated to perform the accuracy of test- ing you require. Ensuring this likely requires some understanding of the specifications of the equip- ment you propose to use, and if this is not clear, then you need to consult with the vendor. Too often the authors see people try to test scenarios at a level of accuracy totally beyond the capability of the test measurement equipment. With 5G increasing the interface speeds, many devices in the radio access network now carry tim- ing over 25-GE and 100-GE interfaces. As the ITU-T increases the accuracy requirements in later versions of its recommendations, the vendors need to produce equipment that is capable of accur- ately testing it. Figure 12-10 shows one such device from Calnex, a Paragon-neo that allows con- nection of a larger choice of interface options, such as 25-GE (SFP28), 40-GE (QSFP+), and 100- GE (QSFP28 and CFP4) optics. Paragon neo Calnex Figure 12-10 Calnex Paragon-neo Other types of equipment might be used in some testing situations, and they will be mentioned where appropriate. A good example would be a standalone frequency or time interval counter or devices used for TDM testing, such as a bit error rate tester (BERT) or frequency tester. But you can do pretty much everything you would need with one of the previously mentioned dedicated timing testers. Note that some vendors for test equipment enable different features with optional licenses, SO be sure to purchase the capability that you need. One more point is that Calnex Solutions produces a wide range of very educational material on tim- ing, PTP, and testing. Anybody who wants to get serious with testing timing is strongly recommen- ded to refer to the Calnex technical library (a link is pro