[2] RFC 781 - Specification of the Internet Protocol (IP) timestamp option, 2021-04-11T09:27:02.000Z, 2021-04-21T08:52:47.659Z https://tools.ietf.org/html/rfc781

[1] RFC 792 - Internet Control Message Protocol, 2021-04-04T07:48:00.000Z, 2021-04-16T07:35:31.216Z https://tools.ietf.org/html/rfc792#page-16

[4] RFC 3252 - Binary Lexical Octet Ad-hoc Transport, 2019-03-03T20:11:48.000Z, 2021-04-21T09:02:34.530Z https://tools.ietf.org/html/rfc3252#page-11

[3] TCP Timestamps とは違います。