ABSTRACT
Examples of service systems range from complex interconnected networks such as computer communication networks, transportation systems, theme parks, etc., to simpler individual units such as a barber shop, repair shops, theaters, restaurants, hospitals, hotels, etc. In all these examples, two key players emerge, namely, the service provider and users. As the names suggest, the users receive service provided by the service provider. Users (also called customers if there is money involved) do not necessarily have to be humans; they could be other living or nonliving entities. Further, users do not have to be single individuals, they could be part of a group (such as in a multicast session, in a restaurant, at a play, etc.). On the same token, for a given system, there could be zero, one, or many service providers. Although most services are such that they are owned by a single entity (the one to blame if things go wrong), there are some (including the Internet) that are owned by several groups.
