Phone networks use circuit switching: an end-to-end circuit must be set up before the call can begin. A fixed share of network resources is reserved for the call, and no other call can use those resources until the original connection is closed. This means that a long silence between two teenagers uses the same resources as an active negotiation between two fast-talking lawyers. One advantage of circuit-switching is that it enables performance guarantees such as guaranteed maximum delay, which is essential for real-time applications like voice conversations. It is also much easier to do detailed accounting for circuit-switched network usage.