tem employs specialized equipment for supervisory control and data acquisition (SCADA) to monitor volumes, pressures, and temperatures, as well as the oper- ating status of pipeline facilities. SCADA equipment monitors the volume of gas being supplied to the system and the volume of gas delivered to customers. SCADA also grants the system monitor the ability to quickly identify and react to equip- ment malfunctions and the capability to remotely start or stop certain compressors, thereby changing flow volumes to meet changes in customer demand for natural gas (Interstate Natural Gas Association of America 2007, p. 83). SCADA systems are used in "water management systems, electric power, traffic signals, mass transit systems, environmental control systems, and manufacturing systems" (techFAQ, 2009). The discussion of central control of pipeline operations shows how the capaci- ties of the pipelines and the compressors combine to deliver natural gas. Clearly, the effect of an individual network element such as a compressor on pipeline services is not easily separated from the effect of the network. When a pipeline network is constructed, compressors are incorporated into the design and structure of the network. When a pipeline is operated, the pipeline's central control coordinates The Design and Costs of Networks the functioning of the compressors to achieve desired flow volumes through the system. b. Telecommunications The engineering of telecommunications networks presents problems of even greater complexity than for a natural gas transmission system. Calls must be routed between specific initial and terminal points. Calls are of random duration, origin, and des- tination. Telecommunications systems consist of many different types of elements of varying complexity ranging from sophisticated computer-controlled exchanges to basic parts such as regenerators (Ericsson 1997, pp. 349-50). The construction of such a complicated system requires an integrated design that allows diverse net- work elements to work togethe