ation driving the Long Term Evolution (LTE) and 5G mobile standards MEF Forum (MEF), developing services across automated networks O-RAN Alliance, for radio access network (RAN) front-haul network specifications Internet Engineering Task Force (IETF), for Internet-related standards There is a lot more information on each of these organizations and their contributions in Chapter 4. Within the ITU-T, Q13/15 is responsible for the following major recommendations related to timing: Definitions, architecture, and functional models: G.781, G.781.1, G.810, G.8260, G.8265, G.8273, G.8275 Network performance: G.823, G.824, G.825, G.8261, G.8261.1, G.8271, G.8271.1, G.8271.2 Clocks: G.811, G.811.1, G.812, G.813, G.8262, G.8262.1, G.8263, G.8266, G.8272, G.8272.1, G.8273.1, G.8273.2, G.8273.3, G.8273.4 PTP profiles: G.8265.1, G.8275.1, G.8275.2 Other documents and recommendations: G.703, G.8264, GSTR-GNSS, Supplement 68- Synchronization Operations, Administration and Maintenance (OAM) Requirements This chapter will go through each of these recommendations and documents in turn. Q13/15 also covers several other recommendations, which are not relevant to this topic and SO will not be covered. The three-digit recommendations, G.7xx and G.8xx, are primarily relevant for TDM and physical methods of timing transport, whereas the four-digit recommendations tend to be for packet-based transport, including synchronous Ethernet (SyncE). This is where the two definitions overlap a little, as SyncE uses a packet-based transport but is still a physical method of frequency transfer. Most of the recent development effort of Q13/15 is in packet-based recommendations, although it has been involved in other efforts-for example, the enhanced PRC (ePRC) definition in G.811.1. Table 8-1 shows the categorization of only the packet-based recommendations and the role of each recommendation in the overall solution architecture. Further information on the non-packet (phys- ical) recommendations is provided in the upcoming section "Physical and TDM V