<networking, programming> (TLI, or "Transport Level Interface") A protocol-independent interface for accessing network facilities, modelled after the ISO transport layer (level 4), that first appeared in Unix SVR3. TLI is defined by SVID as transport mechanism for networking interfaces, in preference to sockets, which are biased toward IP and friends. A disavantage is that a process cannot use read/write directly, but has to use backends using stdin and stdout to communicate with the network connection. TLI is implemented in SVR4 using the STREAMS interface. It adds no new system calls, just a library, libnsl_s.a. The major functions are t_open, t_bind, t_connect, t_listen, t_accept, t_snd, t_rcv, read, write. According to the Solaris t_open man page, XTI (X/OPEN Transport Interface) evolved from TLI, and supports the TLI API for compatibility, with some variations on semantics. (1999-06-10)

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).

transport layer