Efforts within the ATM Forum and the ITU-T have led to the definition of signalling interfaces between switches called the Network-to-Network Interfaces (NNIs). Of these, the ATM Forum's Private Network-to-Network Interface is intended for private networks and contains interfaces both for the exchange of routing information and for connection control [#!PNNI:96!#]. The public NNI developed by the ITU-T serves as a demarcation point between two public networks. It is based on a modified version of Signalling System 7 and uses preassigned VCIs for signalling.
Closely related to this and the sort of interoperability discussed in this paper are the ATM Forum's efforts regarding the broadband inter-carrier interface (B-ICI). B-ICI is similar to a NNI except that NNI is really a switch-to-switch interface, designed to makes switches from different vendors work together, so that if these switches are located in the same network, the NNI needs to exist inside the network as well. B-ICI on the other hand is only concerned with internetworking between public carriers and need never exist within the network. B-ICI specifies a wide range of physical layers over which the ATM layer can run and also particular adaptation layers for common inter-carrier services such as Frame Relay.
In [#!Rooney:98a!#] a mechanism very similar to the simple hop-by-hop solution of section is described. It is used to provide interoperability between a home-grown MCA and other MCAs.