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In telecommunications, a network-to-network interface (NNI) is an interface which specifies signaling and management functions between two networks. An NNI circuit can be used for interconnection of signalling (e.g. SS7), Internet Protocol (IP) (e.g. MPLS) or ATM networks.
Basically, NNI is used for interconnection of P Routers (class 4 or higher provider core) in signaling or GMPLS networks. NNI can be used for interconnection of two VoIP nodes. In GMPLS case, that could be Back-to-Back or EBGP or mixed NNI connection scenarios, depending on what type of VRF exchange is used for interconnection. In case of Back-to-Back, VRF it is necessary to create VLANs and subsequently sub-interfaces (VLAN headers and DLCI headers for Ethernet and frame relay network packets) on the each interface used for the NNI circuit. In case of eBGP NNI interconnection, P routers are taught how to dynamically exchange VRF records without VLAN creation.
In cases of mixed or full-mesh scenarios, other NNI types are possible.
Note that there could be different encapsulation types for NNI interconnection, but Ethernet (GigE) and frame relay are basically used.
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