Implementing SIGTRAN for Linux Fast-STREAMS Design for Linux

1 Background UNIX networking has a rich history. The TCP/IP protocol suite was first implemented by BBN using Sockets under a DARPA research project on 4.1aBSD and then incorporated by the CSRG into 4.2BSD [? ]. Lachmann and Associates (Legent) subsequently implemented one of the first TCP/IP protocol suite based on the Transport Layer Interface (TLI) [? ] and STREAMS [? ]. Two other predominant TCP/IP implementations on STREAMS surfaced at about the same time: Wollongong and Mentat. 1.1 STREAMS STREAMS is a facility first presented in a paper by Dennis M. Ritchie in 1984 [? ], originally implemented on 4.1BSD and later part of the Bell Laboratories Eighth Edition UNIX, incorporated into UNIX System V Release 3 and enhanced in UNIX System V Release 4 and further in UNIX System V Release 4.2. STREAMS was used in SVR4 for terminal input-output, pseudo-terminals, pipes, named pipes (FIFOs), interprocess communication and networking. STREAMS was used in SVR3 for networking (in the NSU package). Since its release in System V Release 3, STREAMS has been implemented across a wide range of UNIX, UNIX-like and UNIX-based systems, making its implementation and use an ipso facto standard. STREAMS is a facility that allows for a reconfigurable full duplex communications path, Stream, between a user process and a driver in the kernel. Kernel protocol modules can be pushed onto and popped from the Stream between the user process and driver. The Stream can be reconfigured in this way by a user process. The user process, neighbouring protocol modules and the driver communicate with each other using a message passing scheme. This permits a loose coupling between protocol modules, drivers and user processes, allowing a third-party and loadable kernel module approach to be taken toward the provisioning of protocol modules on platforms supporting STREAMS. On UNIX System V Release 4.2, STREAMS was used for terminal input-output, pipes, FIFOs (named pipes), and network communications. Modern UNIX, UNIX-like and UNIX-based systems providing STREAMS normally support some degree of network communications using STREAMS; however, many do not support STREAMSbased pipe and FIFOs or terminal input-output without system reconfiguration. UNIX System V Release 4.2 supported four Application Programming Interfaces (APIs) for accessing the network communications facilities of the kernel: Transport Layer Interface (TLI). TLI is an acronym for the Transport Layer Interface [? ]. The TLI was the nonstandard interface provided by SVR3 and SVR4, later standardized by X/Open as the XTI described below. This interface operated differently than the XTI in subtle ways, and is now deprecated. X/Open Transport Interface (XTI). XTI is an acronym for the X/Open Transport Interface [? ]. The X/Open Transport Interface is a standardization of the UNIX System V Release 4, Transport Layer Interface. The interface consists of an Application Programming Interface implemented as a shared object library. The shared object library communicates with a transport provider Stream using a service primitive interface called the Transport Provider Interface[? ]. While XTI was implemented directly over STREAMS devices supporting the Transport Provider Interface (TPI) [? ] under SVR4, several non-traditional approaches exist in implementation: Berkeley Sockets. Sockets uses the BSD interface that was developed by BBN for the TCP/IP protocol suite under DARPA contract on 4.1aBSD and released in 4.2BSD. BSD Sockets provides a set of primary API functions that are typically implemented as system calls. The BSD Sockets interface is non-standard, operated differently from the POSIX interface in subtle ways, and is now deprecated in favour of the POSIX/SUS standard Sockets interface. POSIX Sockets. Sockets were standardized by X/Open, later the OpenGroup, and IEEE in the POSIX standardization process. They appear in XNS 5.2 [? ], SUSv1 [? ], SUSv2 [? ] and SUSv3 [? ]. POSIX/SUS Sockets is now the common application environment for accessing networking, deprecating the XTI for TCP/IP networking applications. ∗[email protected] 1. AIX, for example. 2. HP-UX, for example. 3. http://www.opengroup.org/