ITU-T H.248.84

Abstract

NAT traversal (NAT-T) support by ITU-T H.248 media gateways (MG) is an established capability for such network elements positioned in the IP infrastructure of next generation networks (NGN) and IP multimedia subsystem (IMS) networks. In [ITU-T H.248] there are several methods for NAT-T, for example: <br>&#8211; [ITU-T H.248.37] IP NAPT traversal package; and <br>&#8211; [ITU-T H.248.50] NAT traversal toolkit packages. <br>However, these do not define any methods for NAT-T in peer-to-peer (P2P) services, i.e., for ITU-T H.248 MGs located within the end-to-end P2P IP path providing NAT traversal support for remote NAT devices (also located in the P2P IP path). <br>In scope of this Recommendation are NAT-T techniques as detailed by [b-IETF RFC 5128].&#160; <br><strong>Problem statement</strong> <br>The problem of providing NAT-T in P2P is described in [b-IETF RFC 5128]. However, this IETF RFC does not consider scenarios where ITU-T H.248 gateways may be located in the end-to-end IP paths of a P2P service. <br>The ITU-T H.248 MG may provide help for NAT-T, e.g., by <br>&#8211; the capability of reporting observed IP transport addresses according to the [ITU-T H.248.37] <em>address reporting</em> package; or/and <br>&#8211; a bearer-level application level gateway (ALG) function according to [ITU-T H.248.78]. <br>However, the usage of either or both is conditional, dependent on: network architecture, IP applications, protocol awareness by ITU-T H.248 MG, remote NAT behaviour, etc. <br>It should also be noted that a bearer-level application layer gateway (ALG) itself may not be sufficient for NAT-T scenarios in scope of this Recommendation. <br>The bearer-level ALG might be a beneficial and effective NAT-T support function. However this Recommendation provides NAT-T methods for scenarios without the usage of [ITU-T H.248.78]. This is in order to respect the principle of "network unawareness" (i.e., "L4 payload agnostic") concerning the (bearer-level) IP application protocol in P2P scenarios. <br><strong>Example network applications</strong> <br>Example network applications are for instance, ITU-T H.248 gateways located between different IP networks (so called ITU-T H.248 border gateways) which support over-layered peer-to-peer services.