Typically a number of components are required to produce a service. These components may be produced by different networks. Then Pacific Bell carries it to the San Francisco subscriber. These are all complementary components of the network. See the example of the information superhighway .
Networks exhibit positive consumption and production externalities.
Please give examples. Network externalities can arise directly or indirectly. This is an example of a direct network externality. In these cases, the value of an operating system is higher when there is a large number of applications that can run under it. The combination of these effects makes the value that a consumer receives from an OS higher when the sales of the OS are higher.