This Recommendation defines the capability and procedures for determining whether an endpoint is located behind a network address translator (NAT) or firewall (FW) and to determine the characteristics of the NAT/Firewall device. This feature detects the NAT/Firewall characteristics in order to allow a gatekeeper to determine whether it is possible to stream media directly between two endpoints. If used in conjunction with [ITU-T H.460.24]@ the scalability of [ITU-T H.460.18]/[ITU-T H.460.19] may be extended to allow media to flow directly between ITU-T H.323 endpoints@ thus avoiding the necessity to proxy media through an ITU-T H.460.19 server.