 equipment. They can also provide line timing to down- stream clocks as SEC nodes can. In fact, the SDH clock hierarchy shown in Figure 6-6 also applies to EEC nodes (substituting EEC instead of SEC). Further details on SyncE and the EEC clock can be found in ITU-T G.8262. See Chapter 8 for more details on the ITU-T recommendations The evolving 5G wireless architecture and some of the newer features and services that it makes possible will require higher performance of timing and frequency synchronization. To define and meet the much tighter synchronization requirements of 5G in front-haul networks, the ITU-T is de- fining a new set of enhanced clocks. These newer clocks have around an order of magnitude better performance than the clocks defined for pre-5G networks. The frequency synchronization aspects of these "enhanced clocks" are covered by the new enhanced synchronous Ethernet. 6.5 Enhanced Synchronous Ethernet Over the past several years, the ITU-T defined (in G.8262.1) the enhanced Ethernet equipment clock (eEEC) that supports an improved version of SyncE called enhanced synchronous Ethernet (eSyncE). This eEEC is the newer, more accurate alternative to the older EEC clock that was defined in ITU-T G.8262. As explained in Chapter 5, different ITU-T specifications define the performance requirements for each type of clock. These performance requirements are primarily for clock accuracy, noise transfer, holdover performance, noise tolerance, and noise generation. For the eEEC, the ITU defines per- formance specifications that are much stricter than those for the EEC to ensure that the new clock delivers better performance. The ITU-T G8262.1 recommendation is relatively recent (January 2019), and the authors expect that it might take some time for the equipment to fully comply with the performance requirements specified in this recommendation. Note that you must take care when deploying frequency synchronization over Ethernet using a mix- ture of clock nodes with different performance levels. Imagine a netwo