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. This document describes the architectural framework for applying MPLS to transport networks. It is joint work with the ITU-T. The document does not contain any normative statements in the RFC 2119 sense; presumably this is because the framework nature of the document and/or the coupling to ITU-T, but it is a little concerning as there are a number of "must", "should" and "may" statements in the document that do look normative to me (e.g. "In cases where a MAC address is needed, the sending node must set the destination MAC address to an address that ensures delivery to the adjacent node."). The security considerations section is very brief and consists mainly of references to other, related documents' security considerations sections. I think it could have been beneficial if it had covered security aspects stemming from the architectural framework and not only force the reader to turn to the component documents. For example, since G-ACh traffic is indistinguishable at the server layer from data traffic, is it possible to craft data traffic messages that confuse a server to believe it is G-ACh? Or, does the bandwidth sharing between control traffic and user data traffic have any security implications? Also, the NNI traffic may involve signaling over the same channel as user data traverse which may cause similar concerns (I am not an expert on MPLS or TP so these threats may well not be realistic, however they serve only as examples). (A minor editorial suggestion: Perhaps better if the list of acronyms in Section 1.3 would be in alphabetical order?) -- Magnus