-BC clocks. For further information on T-BC performance, see the section on G.8273.2 in Chapter 8. See the Chapter 3 section "Sources of Frequency, Phase, and Time" for further details on the PRTC. Details of the performance of the PRTC and the ePRTC are covered in G.8272 and G.8272.1, respectively. 11.5 Timing Security and MACsec The Chapter 7 section "PTP Security" discusses the pros and cons of implementing security protec- tions for the PTP-based timing distribution. It also covers the security features newly adopted in the IEEE 1588-2019 edition of PTP. See 1588-2019 Section 16.14, "PTP integrated security mechan- ism," and the informative Annex P from the same document. However, Chapter 7 also explains that there is little use to encrypting PTP messages because the data in the messages is well known and even encrypted PTP messages can be readily detected by their behavior and size. It also points out that a delay attack is a much simpler and effective method to corrupt a PTP timing signal than any complex technical attack. But there is theory and there is reality and then there is politics. In previous generations of mobile networks, the totality of the equipment to run the network was largely under the control of the MSP. Most of it was housed in large, protected facilities, while the cell site was a locked container at the bottom of a tower surrounded by a barbed wire fence, observed by cameras and protected with alarms. Links between the two were either some cable buried underground or microwave dishes on the top of towers and buildings. With the increasing densification of the 5G network and the adoption of many more small cell-type radio devices in a wide variety of facilities, the MSP can no longer guarantee the physical security of portions of the network. This means it is becoming easier for third parties to get access to the links feeding into the equipment and even to the device itself, especially in the FH and MH. For this reason, most MSPs are looking at encrypting portions of their RAN to safeg