This Recommendation covers the technical requirements for narrow-band visual telephone services defined in H.200/AV.120-series Recommendations, in those situations where the transmission path includes one or more packet-based networks, each of which is configured and managed to provide a non-guaranteed Quality of Service (QOS) which is not equivalent to that of N-ISDN such that additional protection or recovery mechanisms beyond those mandated by ITU-T H.320 need be provided in the terminals. It is noted that ITU-T H.322 addresses the use of some other LANs which are able to provide the underlying performance not assumed by the H.323/H.225.0 Recommendations. This Recommendation describes how audio, video, data, and control information on a packet-based network can be managed to provide conversational services in H.323 equipment. Annex G describes methods to allow address resolution between administrative domains in H.323 systems for the purpose of completing calls between the administrative domains. An administrative domain exposes itself to other administrative domains through a type of logical element known as a border element. Products claiming compliance with Version 4 of H.225.0 (this version) shall comply with all of the mandatory requirements of this Recommendation. Version 4 products can be identified by H.225.0 messages containing a protocolIdentifier value of {itu-t (0) recommendation (0) h (8) 2250 version (0) 4}