This chapter describes the Transport Layer Interface (TLI) and the X/Open Transport Interface (XTI). Advanced topics such as asynchronous execution mode are discussed in Advanced XTI/TLI Topics.
Some recent additions to XTI, such as scatter/gather data transfer, are discussed in Additions to the XTI Interface.
The transport layer of the OSI model (layer 4) is the lowest layer of the model that provides applications and higher layers with end-to-end service. This layer hides the topology and characteristics of the underlying network from users. The transport layer also defines a set of services common to many contemporary protocol suites including the OSI protocols, Transmission Control Protocol and TCP/IP Internet Protocol Suite, Xerox Network Systems (XNS), and Systems Network Architecture (SNA).
TLI s modeled on the industry standard Transport Service Definition (ISO 8072). It also can be used to access both TCP and UDP. XTI and TLI are a set of interfaces that constitute a network programming interface. XTI is an evolution from the older TLI interface available on the SunOS 4 platform. The Solaris operating system supports both interfaces, although XTI represents the future direction of this set of interfaces. The Solaris software implements XTI and TLI as a user library using the STREAMS I/O mechanism.