Connectivity between the different access networks is the key functionality that a backbone network infrastructure has to provide; this applies particularly to the anticipated migration of circuit and packet switched access networks. A backbone network ought to support the provision of globally accessible services independent of the attached access networks; it should also provide accessibility to any type of communication or data service a user may want to access. It is expected that any possible core network will be based on the Internet protocol (IP) suite, and at least the border gateways of access networks will be connected to the core network using IP. Apart from these general demands, core networks will require sufficient intelligence to cover issues like unified accounting and billing of users who employ the services of different access network providers. Another issue with an IP-based backbone network is asset ownership. Although from a technological point of view the existing Internet model may be applied, it is arguable whether this model will satisfy the commercial interests of network providers; a distribution ofresponsibilities and services may be a solution. Other technical challenges like local access to data, automatic recovery and synchronization of wireless transactions, and the implementation of [home] network provider policy tools to support the roaming of users into another provider’s access network, will also have to be supported by the backbone infrastructure. The distributed nature of the Internet already provides the basic means for supporting these features, but connecting all possible active networks will require the introduction of additional management mechanisms that ensure synchronization of distributed subscriber and service databases.

Apart from these technical challenges, there are also commercial issues that have to be overcome: interconnection agreements between the providers of different parts of the networks and the conditions for these agreements have to be defined. So far, within the telecommunications industry there have been interconnection agreements between horizontally organized networks (e.g. in the North American market between GSM and DAMPS providers); however with the incorporation of vertically organized networks, essentially involving different industries with their own cultures and implicit assumptions, such mutual agreements will prove more difficult to achieve (e.g. agreements between local WLAN network providers and satellite or cellular access network providers, etc.)