Hi, I have reviewed this document as part of the security directorate's ongoing effort to review all IETF documents being processed by the IESG. These comments were written primarily for the benefit of the security area directors. Document editors and WG chairs should treat these comments just like any other last call comments. NTP format timestamps are used by several RTP protocols for synchronisation and statistical measurements. This memo specifies SDP signalling identifying timestamp reference clock sources and SDP signalling identifying the media clock sources in a multimedia session. I see no security concerns with this document. I believe the security considerations section explains the ramifications of trusting unverified clock sources. Note, there is a typo in the Security Considerations section: Enough devices fraudulently assigned to a specific clock source (e.g. a particular IEEE 1588 grandmaster) may, however, constitute a successful a denial of service attack on that source. I think this should read "...constitute a successful denial..." (the extra "a" between "successful" and "denial" should be removed). -derek -- Derek Atkins 617-623-3745 derek at ihtfp.com www.ihtfp.com Computer and Internet Security Consultant