When reading through the "Q.931 part" of H.225.0, the text for the "Q.931" messages specifies "who" is supposed to send and act on the messages. Strangely enough, these seem to be somewhat inconsisten with each other. From the list below (extracted from H.225.0), some messages are sent by the user (???), some messages are sent by (any???) H.323 entity, some messages are sent by a specific H.323 entity and some messages are sent by "something" unspecified. Alerting: "This message may be sent by the calling user..." Call Proceeding: "This message may be sent by the called user..." Connect: "This message shall be sent by the called entity..." Information: "This message may be sent by an H.323 entity..." Progress: "This message may be sent by an H.323 gateway..." Release Complete: "This message shall be sent by a terminal..." Setup: "This message shall be sent by a calling H.323 entity..." Setup Acknowledge: "This message may be sent by an H.323 entity..." Status: .... Status Inquiry: ... First of all, it is not correct to state that any of the messages are sent by the user. Secondly, according to the definition in H.323, an "H.323 Entity" is: "Any H.323 component, including Terminals, Gateways, Gatekeepers, MCs, MPs, and MCUs". From the definition for Endpoint it follows that only a Terminal, a Gateway an an MCU can call and be called. This seems to somewhat contradict the definition of which messages can be sent by by which "components". I.e. this seems to restrict the components that are allowed to send H.225.0/Q.931 messages to Endpoints. Thirdly, a Release Complete message can only be sent by a terminal. I can not imagine that this is correct. I would imagine that Gateways, MCUs and even Gatekeepers are also allowed to send this message. Is there anyone who can shed some light on the above? Regards, Frank ----------------------------------------------------- Frank Derks |Tel +31 35 6893238 | Advanced Development |Fax +31 35 6891030 | Philips Business Communications|P.O. Box 32 | |1200 JD Hilversum | |The Netherlands | ----------------------------------------------------| E-mail: mailto:frank.derks@philips.com | WWW: http://www.sopho.philips.com | -----------------------------------------------------