 cover security and trust of the packet network in general; there are ample references on that topic. One source you might find especially helpful for background is IETF RFC 7384, which covers the security requirements of both PTP and NTP. The security disadvantages of using the transport network for timing fall into two categories: The end-to-end timing solution may require a significant number of GNSS receivers or other radio equipment as sources of time. This equipment can be quite vulnerable to jamming, not only by state actors with military means, but even to an unsophisticated attack. This aspect will be covered in "Chapter 11. 5G Timing Solutions", when looking at deployment tradeoffs. PTP traffic is not like any other packet traffic because it is time sensitive at the sub-micro- second level. The time sensitivity means that it is vulnerable to any form of delay in transmis- sion, especially if the delay is asymmetric (different length of delay in each direction). A bad actor only needs to delay the packet stream in one direction by a few microseconds to take all downstream devices out of alignment. There is very little that can be done to mitigate this (or even detect it) beyond the basic access control measures applicable to all other packet networks. Beyond that, the vulnerability of PTP is not as great. The data in most PTP messages is primarily timestamps, SO the data is not sufficiently sensitive to require strong encryption. Some propose the use of encryption to "hide" from any attacker the fact that sensitive PTP packets are in the data stream. That method does not help, as the innate characteristics of PTP traffic make it easy to de- tect, even when encrypted, allowing a simple delay attack. See the white paper "Encryption is Fu- tile" (listed in the "References" section) for further details. The other aspect is verification of the timestamps, such as the need to provide source authentication, message integrity protection (to ensure it is unaltered), and defense against replay attacks. There is a 