ITU-T H.248.64 PDF

An ITU-T H.248 media gateway (MG) may provide ITU-T H.248 IP-to-IP contexts, which implies an IP forwarding function (in the ITU-T H.248 bearer path or IP data path). There are many different forwarding functions possible, dependent on the set of packet processing functions executed, and dependent on whether the MG behaves as a host or a hop system. Two basic forwarding functions may be identified:

– Back-to-back IP host (B2BIH) mode.

– IP router (IPR) mode.

The B2BIH mode is inherently supported by the ITU-T H.248.1 protocol architecture; the IPR mode is addressed within this Recommendation. In the IPR mode, if IP packets are routed between a private network and a public network, network address translation (NAT) functionality is also supported by this Recommendation.

Applicability of the B2BIH mode

This mode is applied in case that an ITU-T H.248 context provides either:

– a single IP host entity (like a physical-to-IP context for residential, access or trunking media gateways); or

– back-to-back host configurations as, e.g., required for service interworking [ITU-T Y.1251] above the IP layer (between two IP domains) or L3 address translations, i.e., whenever the IP stack must be entirely terminated.

Applicability of the IPR mode

This mode provides the basic IP router functions and may be also applied with additional routing/forwarding behaviours, e.g.:

– forwarding of session-individual IP bearer traffic;

– forwarding of IP-based signalling traffic;

– forwarding of aggregated IP traffic;

– forwarding with specific NAT behaviour;

– MG-embedded IP edge router (IPER);

– MG-embedded DiffServ IP edge router (DER);

– MG-embedded MPLS label edge router (LER);

– congestion control for IP traffic.

This Recommendation supports IP unicast forwarding. Multicast forwarding (see clause 5.2.1.3 of [IETF RFC 1812]) is basically covered by the design of the ITU-T H.248.64 packages, but details are left for future study.