the next exchange in the sequence. The key to end-to-end signaling is the concept of "leading register." This is the register (control unit) in the originating exchange that controls the call routing until a speech path is setup to the terminating exchange before releasing to prepare for another call setup. For example, consider a call from subscriber X to subscriber Y: Originating Terminating exchange Tandem exchanges exchange 7.6 EFFECTS OF NUMBERING ON SIGNALING The telephone number of subscriber Y is 345-6789. The sequence of events is as follows using end-to-end signaling: A register at exchange OE receives and stores the dialed number 345-6789 from subscriber X. Exchange OE analyzes the number and then seizes a trunk (junction) to exchange B. It then receives a "proceed-to-send" signal indicating that the register at B is ready to receive routing information (digits). Exchange OE then sends digits 34, which are the minimum necessary to effect correct transit. Exchange B analyzes the digits 34 and then seizes a trunk to exchange C. Exchanges OE and C are now in direct contact and exchange B's register releases. Exchange OE receives the "proceed-to-send" signal from exchange C and then sends digits 45, those required to effect proper transit at C. Exchange C analyzes digits 45 and then seizes a trunk to exchange TE. Direct communication is then established between the leading register for this call at OE and the register at TE being used on this call setup. The register at C then releases. Exchange OE receives the "proceed-to-send" signal from exchange TE, to which it sends digits 5678, the subscriber number. Exchange TE selects the correct subscriber line and returns to A ring-back, line busy, out of order, or other information after which all registers are released. Thus we see that a signaling path is opened between the leading register and the terminating exchange. To accomplish this, each exchange in the route must "know" its local routing arrangements and request from the leading register those digits i