 both to the technical interface and to the commercial arrange- ments between two network operators providing service. interface A boundary between two pieces of equipment across which all signals that pass are carefully defined. The definition includes the connector signal levels, impedance, timing, sequence of operation, and meaning of signals. interior routing Routing that occurs within an autonomous system. international business service A satellite-based service at up to 8Mbps. Services include data, fax, digital voice, and video- and audioconferencing. international gateway A device that connects calls between different countries. international number Digits that have to be dialed after the international prefix to call a subscriber in another country; that is, the country code followed by the subscriber's national number. internet A collection of packet-switching networks interconnected by routers along with pro- tocols that allow them to function logically as a single, large, virtual network. Internet The worldwide Internet consisting of large national and regional backbone net- works, local Internet service providers, and IP networks. Internet 2 A network that replaces what the original Internet was for-the academic net- work. Internet 2 acts as a testbed for many of the latest and greatest technologies. Universities stress-test Internet 2 to determine how applications perform and which technologies suit which applications or management purposes best. Internet-based VPN Internet-based VPN A VPN composed of multiple ISPs that provide local access services in defined geographical regions. Because it requires an enterprise to receive end-to-end services from multiple suppliers, performance is difficult to control and guarantee. interoffice channels A portion of a leased circuit between IXC exchanges. interoffice trunk A direct trunk between local exchanges (Class 5 offices) or between tan- dem, toll, or international exchanges. Also called interexchange trunk. interoperability The ability to exchange informa