IS-41, also known as ANSI-41, is a mobile, cellular telecommunications system standard to support mobility management by enabling the networking of switches. ANSI-41 is the standard now approved for use as the network-side companion to the wireless-side AMPS (analog), IS-136 (Digital AMPS), cdmaOne, and CDMA2000 networks. It competes with GSM MAP, but the two will eventually merge to support worldwide roaming. IS-41 facilitates inter-switch operations like handoff and roaming authentication. IS-41 evolved through revisions 0, A, B, C, D, and E with increasingly robust and distributed call processing between switches and their roamer databases. To describe IS-41 messaging requires special terminology to designate the telephone call's originating and terminating switch, called an MSC (anchor-MSC, candidate-MSC, homing-MSC, serving MSC and target MSC) and databases called VLR and HLR. For handoffs the messaging is between switches. For roaming and authentication, the messaging would include an HLR and a VLR. In both cases, the PSTN may be needed to carry messaging.
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