On 07/01/2013 12:42, Stewart Bryant wrote: > Indeed an interesting additional question. > > My view is that you MUST NOT use RFC2119 language, unless you MUST use > it, for exactly that reason. What is important is "on the wire" (a term > that from experience is very difficult to define) inter-operation, and > implementers need to be free to achieve that though any means that suits > them. Agreed. Imagine the effect if the TCP standard had said that a particular congestion control algorithm was mandatory. Oh, wait... ... RFC 1122 section 4.2.2.15 says that a TCP MUST implement reference [TCP:7] which is Van's SIGCOMM'88 paper. So apparently any TCP that uses a more recent congestion control algorithm is non-conformant. Oh, wait... ... RFC 2001 is a proposed standard defining congestion control algorithms, but it doesn't update RFC 1122, and it uses lower-case. Oh, wait... RFC 2001 is obsoleted by RFC 2581 which obsoleted by RFC 5681. These both use RFC 2119 keywords, but they still don't update RFC 1122. This is such a rat's nest that it has a guidebook (RFC 5783, "Congestion Control in the RFC Series") and of course it's still an open research topic. Attempting to validate TCP implementations on the basis of conformance with RFC 2119 keywords would be, well, missing the point. I know this is an extreme case, but I believe it shows the futility of trying to be either legalistic or mathematical in this area. Brian