ITU-T Recommendations

Recommendation ITUT H.460.24 enables an ITUT H.323 gatekeeper to formulate a decision to enable direct media flows between ITUT H.323 endpoints that reside behind network address translator (NAT)/firewall (FW) devices. This extension is used in conjunction with Recommendation ITU-T H.460.18 to facilitate the traversal of media across NAT/FW devices and Recommendation ITU-T H.460.23 to discover the characteristics of NAT/FW devices sitting in front of ITUT H.323 endpoints, reducing the frequency with which media proxy devices (as described in Recommendation ITU-T H.460.19) are needed by allowing direct media connectivity between the endpoints. Connectivity is achieved via the formulation of an intelligent media transmission decision and call signalling that instructs endpoints to initiate media flows in such a manner that a reliable direct media pathway is established, even if one or both endpoints reside behind a NAT/FW device.
Amendment 1 to Recommendation ITU-T H.460.24 further improves conditions where media pathways do not require the services of an intermediary to achieve NAT traversal. New Annex B allows endpoints under certain conditions, after first establishing media flows through an intermediary entity, to probe for a direct route and, if detected, change the media pathway to flow directly between the endpoints freeing up the resources of the intermediary entity.