ITU-T H.460.6 PDF

Seamless operation of IP telephony requires the ability to initiate, redirect and reconfigure media connections in a fast and efficient manner. The reduction of "dead time" and quick response to user actions both demand that media operations be carried out as quickly as possible. For example, a caller might be redirected from an endpoint that does not answer to a voice messaging endpoint that answers automatically. A call may suspend media transfer when a user invokes "hold", then should re-establish media transfer quickly when the user re-joins the call. Similarly, media connections should be quickly reconfigured when a user activates a conference or is switched to an automatic announcement. Such capabilities are available to the simple endpoint type (SET) as described in Annex F of [ITU-T H.323].

This Recommendation provides a method by which an endpoint may negotiate the capability to initiate, rearrange, reconfigure, or close one or more media channels as efficiently and quickly as a SET using the repeated Fast Connect procedures. The advantages of this method, relative to [ITU-T H.245] include:

− the ability of one party to initiate creation of both transmit and receive media channels (not strictly possible in [ITU-T H.245] since the ModeRequest cannot specify a capability, nor can it specify replacementFor);

− the ability of two parties to establish media channels with a single exchange of messages ([ITU-T H.245] requires a three-way to five-way exchange);

− the ability of one party to close a media channel with a single message ([ITU-T H.245] requires two or three messages);

− the ability of one party to redirect a media channel with a single message ([ITU-T H.245] requires at least three);

− optional use of tunnelled ITU-T H.245 to provide capability exchange, master/slave negotiation and non-media controls such as user input indication.

The generic extensible framework (GEF) of [ITU-T H.225.0] is used to negotiate the use of Extended Fast Connect (EFC) procedures. This negotiation may proceed in parallel with tunnelled ITU-T H.245 capability negotiation via the parallelH245Control tunnel and/or standard Fast Connect establishment of one or more initial media channels, as described below.

The term "party" is used herein to refer to either an endpoint or a gatekeeper actively involved in call signalling and media control with another party. The EFC feature may be invoked between endpoints (direct-routed calls or relayed via a gatekeeper), or may involve one or more active gatekeepers or call feature servers. The term "third party" is used to indicate an active party that is not the source or recipient of a media channel.