PATH
This chapter describes what must be done to create STREAMS drivers for the Apple Open Transport networking architecture. It also describes the minimal functionality that must be supported by any driver that works with the Open Transport implementations of AppleTalk and TCP/IP. In this chapter, STREAMS drivers are also called port drivers.
Open Transport uses the STREAMS model for implementing protocols and drivers to provide flexibility for mixing and matching protocols. This approach also allows a wide range of third-party STREAMS modules and drivers to be easily ported to the Open Transport environment.
Part of the flexibility of the STREAMS environment comes from its being a messaging interface with only a few well-defined messages. The most common types of messages are M_DATA (for sending raw data), M_PROTO (for sending normal commands), and M_PCPROTO (for sending high-priority commands). Since STREAMS does not define the content of M_PROTO or M_PCPROTO messages, it is necessary for modules to agree on a message format if they are to communicate. Apple uses the Transport Provider Interface (TPI) message format for most protocol modules and the Data Link Provider Interface (DLPI) for most STREAMS port drivers.
This document assumes familiarity with the STREAMS environment and with the set of STREAMS messages defined by the DLPI specification ( Data Link Provider Interface Specification by Unix International, OSI Workgroup).