Dear all who kindly responded to my question, Now I understand the required minimum versions are coming from the expected use of H.225.0 generic extensibility framework and H.245 generic parameter in the NAT traversal mechanism. ---------- 9.3 Requirements on Signalling and Media Streams b) NAT traversal mechanisms for H.323 multimedia systems shall support no less than ITU-T H.323v3, H.245v7, H.225.0v4, and H.235v3. All later versions of H.323, H.245, H.225.0 and H.235 may be supported. ---------- My original difficulty was in the English expression "shall support no less than version n." It is negative to "less than n" hence equivalent to "n or higher." Furthermore, I understand that version n is a super-set of previous version (n-1), at least in principle ..., in our standards, meaning that version n entity can interwork with any lower version entity. Then the second sentence "may support any later version" would be overlapping with the first sentence. In conclusion, a NAT traversal mechanism with the following H.323 support conforms to this requirement (not mentioning H.245, H.225.0. H.235 for simplicity): a/ v3 b/ v4 c/ v5 d/ v6 e/ v3, v4 ==> equivalent to b/ f/ v3, v5 ==> equivalent to c/ g/ v3, v6 ==> equivalent to d/ h/ v3, v4, v5 ==> equivalent to c/ i/ v3, v4, v5, v6 ==> equivalent to d/ j/ v4, v5 ==> equivalent to c/ k/ v4, v6 ==> equivalent to d/ l/ v4, v5, v6 ==> equivalent to d/ m/ v5, v6 ==> equivalent to d/ I hope I am correct. -- Best regards, OKUBO Sakae e-mail: okubo@aoni.waseda.jp (<== sokubo@waseda.jp, valid until 31 March 2007) Visiting Professor Global Information and Telecommunication Institute (GITI) Waseda University ****************************************************************** Waseda University, YRP Ichibankan 312 Tel: +81 46 847 5406 3-4 Hikarinooka, Yokosuka-shi, Kanagawa-ken Fax: +81 46 847 5413 239-0847 Japan H.323 videoconferencing: arranged by advice ******************************************************************