Transport Layer Interface Explained

In computer networking, the Transport Layer Interface (TLI) was the networking API provided by AT&T UNIX System V Release 3 (SVR3) in 1987 and continued into Release 4 (SVR4). TLI was the System V counterpart to the BSD sockets programming interface, which was also provided in UNIX System V Release 4 (SVR4). TLI was later standardized as XTI, the X/Open Transport Interface.

TLI and Sockets

It was originally expected that the OSI protocols would supersede TCP/IP, thus TLI is designed from an OSI model-oriented viewpoint, corresponding to the OSI transport layer. Otherwise, TLI looks similar, API-wise, to sockets.

TLI and XTI were widely used (?) and, up to UNIX 98, may have been preferred over the POSIX Sockets 5API^[1] with respect to existing standards. However, it was clear at least since the early 1990s that the Berkeley Socket interface would ultimately prevail.^[2] TLI and XTI are still supported in SVR4-derived operating systems and operating systems conforming to branded UNIX (UNIX 95, UNIX 98 and UNIX 03 Single UNIX Specifications) such as Solaris and AIX (as well as the classic Mac OS, in the form of Open Transport). Under UNIX 95 (XPG4) and UNIX 98 (XPG5.2), XTI was the preferred and recommended supported API for new transport protocols.^[3] As a result of deliberations by the Austin Group with the goal of bringing flavors of UNIX that do not provide STREAMS, such as BSD and Linux, under the Single UNIX Specification, the UNIX 03 Single UNIX Specification both declares STREAMS as optional, and declares POSIX Sockets as the preferred API for new transport protocols.

See also

• X/Open Transport Interface, formally standardized successor to TLI.
• X/Open Portability Guide, the predecessor to POSIX
• Computer networking, outlining the major networking protocols

References

• Book: Berny. Goodheart. James . Cox. The magic garden explained: the internals of UNIX System V Release 4, an open-systems design. 1994. Australia. Prentice Hall. 0-13-098138-9.
• Book: Nuss , Branko . RTFM!!! Issue 5.2. 1. 1.0. January 2000. Addison-Wesley. Akron, OH. CAE Specification.
• Book: Pajari , George . 1992. 2nd Printing. 1991. Writing UNIX Device Drivers. Reading, MA. Addison-Wesley. 0-201-52374-4.
• Book: Santa Cruz Operation. The Santa Cruz Operation, Inc.. Santa Cruz, CA. System V Application Binary Interface — Intel386 Architecture Processor Supplement. 4th. 1997. 1995.
• Book: Santa Cruz Operation. The Santa Cruz Operation, Inc.. Santa Cruz, CA. System V Application Binary Interface. 4.1th. 1997. 1995.
• Book: Stevens , W. Richard . UNIX Network Programming. 1990. Prentice-Hall. Englewood Cliffs, N.J.. 0-13-949876-1.
• Book: Stevens , W. Richard . Advanced Programming in the UNIX Environment. Addison-Wesley. Reading, MA. 1993. 1st Edition, 15th Printing. 0-201-56317-7.
• Book: Thomas , Rebecca . Lawrence R. Rogers . Jean L. Yates. Osborne McGraw-Hill. Berkeley, CA. Advanced Programmers Guide to UNIX System V. 1986. 0-07-881211-9.
• Book: UNIX System Laboratories. 1995. 4th. System V Application Binary Interface. UNIX System Laboratories. Englewood Cliffs, N.J..
• Book: Waite Group. Mitchel Waite. 1987. 2nd Printing. UNIX Papers. Indianapolis, IN. Howard W. Sams & Company. 0-672-22578-6.
• Book: Zucker , Steve . Kari Karhi. SunSoft. Mountain View, CA. System V Application Binary Interface—PowerPc Processor Supplement. 1995. 1993.

External links

• The Open Group's XTI standard
• Example client-server application working on Solaris and Linux

Notes and References

1. Book: X/Open Group. Networking Services (XNS) Issue 5.2. 5.2. January 2000. The Open Group. Berkshire, U.K.. CAE Specification.
2. Web site: Andrew L. Russell . 30 July 2013 . OSI: The Internet That Wasn't . IEEE Spectrum . 2021-01-10.
3. Book: X/Open Group. Networking Services (XNS) Issue 5. 5th. February 1997. The Open Group. Berkshire, U.K.. CAE Specification. 1-85912-165-9.