I have reviewed this document as part of the Operational directorate's ongoing effort to review all IETF documents being processed by the IESG. These comments were written with the intent of improving the operational aspects of the IETF drafts. Comments that are not addressed in last call may be included in AD reviews during the IESG review. Document editors and WG chairs should treat these comments just like any other last call comments. This informational document describes requirements for adding an indicator to the SIP protocol data unit (PDU, or a SIP message) that marks the PDU as a candidate for logging. Such marking will typically be applied as part of network testing controlled by the network operator and not used in regular client signaling. However, such marking can be carried end-to-end including the SIP terminals, even if a session originates and terminates in different networks. It's a short, focused and well-written document. It is interesting for the operators of networks that use SIP, as this indicator can be used to trigger testing or debugging in the networks that they operate. It seems that different implications on security and network behavior were considered, although some of them are not explicitly mentioned - such as the potential overload or DoS attacks in case of mis-configuration or malicious configuration of a big number of terminals in a SIP network leading to simultaneous activation of debug modes. It may be good to explicitly mentions these, but otherwise this document is READY from an OPS-DIR perspective.