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

Advanced Mobile Phone System

Advanced Mobile Phone System was an analog mobile phone system standard developed by Bell Labs, and officially introduced in the Americas in 1983, Israel in 1986, and Australia in 1987. It was the primary analog mobile phone system in North America through the 1980s and into the 2000s...

 (analog), IS-136 (Digital AMPS

Digital AMPS

IS-54 and IS-136 are second-generation mobile phone systems, known as Digital AMPS . It was once prevalent throughout the Americas, particularly in the United States and Canada. D-AMPS is considered end-of-life, and existing networks have mostly been replaced by GSM/GPRS or CDMA2000...

), cdmaOne, and CDMA2000

CDMA2000

CDMA2000 is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. The set of standards includes: CDMA2000 1X, CDMA2000 EV-DO Rev. 0, CDMA2000 EV-DO Rev. A, and CDMA2000 EV-DO Rev. B...

 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, and D 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.