over. Again, most operators do not perform these types of tests unless they are primarily interested in the packet emulation of TDM circuits. This book focuses more on SyncE and eSyncE testing for frequency. Functional and Other Most operators are not overly interested in performing a lot of functional tests; however, there are some basic functions that could be relevant and interesting. For example, timing testers often have an option to perform PTP field validation. This ensures that the packets are sent, and protocol fields are filled, according to the standards. Another example might be to validate some of the values in the Announce message, such as the val- ues in the clock accuracy fields (particularly clockClass) when in normal operation versus when in holdover. Similar test cases to validate the ESMC behavior of the clock based on the reception and transmission of a range of SyncE QL values is also interesting. 12.3.1 Testing End-to-End Networks The first major segment of a testing regimen is to test the timing distribution test network against the network limits from the ITU-T. There are three cases to consider: Testing for frequency wander when it has been carried with SyncE or eSyncE over the timing network Testing for frequency wander when it has been carried over the timing distribution network us- ing PTP Testing for phase alignment when it has been carried over the timing distribution network using The following three sections deal with each case in turn. Testing Networks for Frequency Wander (SyncE) The goal of building a timing distribution network is to ensure that the timing signal arrives at the destination at the end of the timing chain with the quality needed by the end application. Therefore, once a proposed design has been accepted, the engineer needs to verify the calculations and as- sumptions underpinning it before deploying it into production. Similarly, once the new design is handed over to operations, situations may arise where the production network needs to be tested. Refer to the 