pecify the allowed limits for these different metrics of time error. The metrics cTE and max|TE| are defined in terms of time (such as nanoseconds). dTE, being the change of the time error function over time, is characterized using TIE and is then compared to a mask expressed in MTIE and TDEV, which defines the permissible limits for that type of clock. Some ITU-T recommendations define allowed limits for a single standalone clock (a single network element), and others specify clock performance at the final output of a timing chain in an end-to- end network. You should not mix these two types of specifications, because limits that apply to the standalone case do not apply to the network case. Similarly, masks used to define the limits on a standalone clock do not apply to the network. This is especially the case when discussing the testing of timing performance, as in "Chapter 12. Operating and Verifying Timing Solutions". For each type and class of standalone clock, all four metrics, max|TE|, cTE, dTE, and TIE, are spe- cified by these standards, while for the network case, max|TE| and dTE are specified. The cTE is not listed for network limits because the limits of max|TE| for the network case automatically in- clude cTE, which might be added by any one clock in the chain of clocks. The ITU-T specifies the various noise and/or time error constraints for almost all the clock types. For each one of the numerous clock specifications, the ITU-T recommendations define all five as- pects for timing characterization of a clock: Noise generation Noise tolerance Noise transfer Transient response Holdover performance Chapter 8 will cover these specifications in more detail. 5.5.1 Topology As shown in Figure 5-23, the setup required for time error measurement testing includes Timing testing equipment that can synthesize ideal reference clock signals. Clock under test that would normally be embedded in a network element. Clock capture and measurement equipment. Most often this is the same equipment that gener- ates the ref