A model for Internet printing

■ The Internet has become more than just a network—it is a distributed computing environment. And, like all robust computing environments, printing is an essential element of the environment. Given the increased sophistication of network printers, there is an ever-increasing need to find instances of printers and printing services, to submit and manage print jobs, and control the logical and physical devices within the network. To that end, the Internet Engineering Task Force (IETF) chartered a working group to define an Internet Printing Protocol (IPP). he network printing experts who formed the IPP working group realized that, within an environment like the Internet, there would be a diverse and heterogeneous set of users, systems, drivers, applications, spoolers, connectivity solutions, devices, and page description languages. Given such a complex set of existing, realworld solutions, the working group members recognized that they would not be successful if they simply ratified an “all inclusive” protocol that supported the loose union of a disjointed set of interfaces, parameters, options, and features. Even though the result might become a standard on paper, there would be, in all practicality, no widespread interoperability. In order to solve this problem, the working group went to great lengths to focus on defining a simple, abstract model that could be used to represent the various and diverse systems and implementations that would be used as the backbone for developing and deploying a standard Internet protocol for printing. The IPP model is centered around the roles and interactions of print service users and printer service providers. The print service users (e.g., clients, applications, printer drivers, report generators) cooperate and interact with print service providers (e.g., physical devices, logical devices, spoolers). The model is simple, yet at the same time, is able to support the many underlying configurations of complex, “n-tier” client/server printing solutions. An important simplifying step in the IPP model is to expose only the key objects and interfaces required for the most basic print jobs. Since many “heavyweight”, technically superior solutions have been overtaken by simpler, “lightweight” easier-to-implement solutions, the IPP model tends to lean toward simplicity rather than completeness. Like the acceptance and growth of HTTP with its many subsequent revisions, many members of the working group knew that they would rather have the problem of needing to enhance a successfully deployed, ubiquitous printing protocol than be “all dressed up with nowhere to go.” This article describes the model elements and operational semantics that form the foundation of IPP. FIGURE 1