grandmaster clock (G.8273.1), the T-BC boundary and T-TSC slave clock (G.8273.2), the T-TC transparent clock (G.8273.3), and the APTS clock (G.8273.4). G.8263: Timing Characteristics of Packet-Based Equipment Clocks ITU-T G.8263 outlines the minimum requirements for the timing functions of the packet-based equipment clock-slave (PEC-S, from G.8265), when timed from a packet-based equipment clock- master (PEC-M, from G.8266). It deals with the packet-based transport of frequency synchroniza- tion as opposed to some physical method. From the scope of the recommendation: This Recommendation focuses on mobile applications, and in particular on the delivery of frequency synchronization for end applications, such as mobile base stations. It supports the architecture defined in [ITU-T G.8265]. Other applications are for further study. This Recommendation includes clock accuracy, packet delay variation (PDV) noise toler- ance, holdover performance and noise generation. G.8263 clocks are typically deployed on the types of networks defined in G.8261.1 and carried us- ing the G.8265.1 PTP profiles. Figure 8-5 shows a simplified view of one of the deployment cases. Master Timing packets Slave Physical layer PEC-M clock input Packet network PEC-S-F PEC-S-F output limits clock Figure 8-5 Topology for G.8263 Packet Equipment Slave Clocks for Frequency The input of the PEC-M is connected to the output from a physical-layer frequency clock (SEC, SSU, PRC). The master generates the packets from this frequency source and sends it to the packet- based equipment clock-slave-frequency (PEC-S-F) that recovers the frequency. G.8263 defines the applicable limits at all points in this network. This recommendation includes the following main topics: Hypothetical reference models Reference points for network limits in packet networks PEC-M network limits PEC-S-F network limits PDV network limits Link to recommendation: https://handle.itu.int/11.1002/1000/13320 G.8266: Timing Characteristics of Telecom Grandmaster Clocks for Fre- quency Sync