At the top right of this illustration, we see a telephone labeled "Correspondent." A blue arrow, labeled 1 and corresponding to numbered steps given in the text on pages 578-9, extends from the Correspondent through a blue cloud representing the public switched telephone network, and leftward from there into a blue cloud representing a home network. In the home network, the blue arrow points to the Home Location Register (HLR). In a step labeled 2, the HLR points back and forth to itself. A blue arrow labeled 3 extends from the HLR through the public switched telephone network and into the Visitor Location Register (VLR) in a visited network. The visited network includes four cellular coverage areas depicted as hexagons, each containing a base transceiver station and sharing mobile subscribers. A blue arrow extends from the VLR to a car labeled "Mobile user."