Toward a Common Meaning

The term network service means many things to many people. Technically speaking, the term was coined by the ISO standards organization within the context of the seven layer network reference model to refer to the set of network layer functions, called the network service access points, available for use by the higher layers: session, presentation, and application. These functions are primarily concerned with the transfer of data across the subnetworks composing the network, independent of the underlying media. Colloquially, the term tends more towards the meaning of a ``service delivered over a network''. Using this definition, everything that moves across a network could be defined as a ``network service'', if a liberal interpretation of the word service, such as ``work done for others as an occupation or business'', were used. Clearly, we need to explicate and constrain this definition in order to be able to rationally discuss, design, document and implement network services in an institutional context.

When the colloquial meaning of ``network service'' is invoked, there usually is a scenario in mind of a person using an application on a computer with a network connection in some kind of client/server model. The key facets of this scenario are:

1.   It involves a person interacting with an application to accomplish a task.
2.   It involves an application running on a computer that has access to a network.
3.   It involves a second network-connected computer application that is willing to provide one or more functions across the network to the first application.

Thus, the common meaning of ``network service'' is that of an application network service, where application-oriented functions (the service protocol) are provided by a designated service server to a specific user application (the service agent) via a network. It is important to note that other network activities could be unintentionally classified as a ``network service'' if the scenario is modified or the definition changed. These could include:

• network layer services, in the ISO sense, namely raw datagram switching. Examples include the Internet Protocol (IP), and the Connectionless Network Protocol (CLNP).
• network control services, such as routing, gateway and host control, and address discovery. Examples include the Open Shortest Path Protocol (OSPF), the Internet Control Protocol (ICMP), the Address Resolution Protocol (ARP), the End System to Intermedate System Protocol (ES-IS) and the Intermediate System to Intermediate System Protocol (IS-IS).

This discussion will thus understand the general term ``network service'' as meaning an application network service.