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100 \s+2Proposal for a Prototype OSI Network Implementation for Berkeley UNIX\s-2 DRAFT of \*(DT
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4 Marshall Kirk McKusick Michael J Karels Susan L. Graham Domenico Ferrari
1 Summary
The release of 4.3BSD in April of 1986 addressed many of the performance problems and unfinished interfaces present in 4.2BSD [Leffler84] [McKusick85]. The Computer Systems Research Group at Berkeley has now embarked on a new development phase to update other old parts of the system. There are three main areas of work. The first is to develop an OSI network protocol suite and to integrate existing ISO applications into Berkeley UNIX. The second is to refine the TCP/IP networking to improve its performance and limit congestion on slow and/or lossy networks. The third is to provide a standard interface to file systems so that multiple local and remote file systems can be supported, much as multiple networking protocols are supported by 4.3BSD.
We are planning to implement prototypes for each of these three main areas of work over the period of this proposal. We plan to do an informal release at the end of the proposal period to interested developers. After incorporating feedback and refinements from the testers, the work will appear in the next full Berkeley release that typically is made about a year after the test release.
Current UNIX Research at Berkeley
Since the release of 4.3BSD in mid 1986, we have begun work on three major new areas of research. Our goal is to apply leading edge research ideas into a stable and reliable implementation that solves current problems in operating systems research. OSI network protocol development
The network architecture of 4.2BSD was designed to accommodate multiple network protocol families and address formats, and an implementation of the ISO OSI network protocols should fit this framework without much difficulty. The outline of the proposal is to implement the OSI connectionless internet protocol (CLNP), and device drivers for X.25, 802.3, and possibly 802.5 interfaces, and to integrate these with an OSI transport class 4 (TP-4) implementation. We will receive an updated ISO Development Environment (ISODE) from Northrop (or any other party) featuring International Standard (IS) versions of utilities, and incorporate these into the Berkeley Software Distribution. ISODE implements the session and presentation layers of the OSI protocol suite, and will include an implementation of the file transfer protocol FTAM. If possible, an X.400 implementation now being done at University College, London and the University of Nottingham will also be available for testing and distribution. This work will include participation in interoperability tests with vendors and users on OSINET.
The tasks to be done include:
The Internet and the Berkeley collection of local-area networks have both grown at high rates in the last year. The Bay Area Regional Research Network (BARRNet), connecting several UC campuses, Stanford and NASA-Ames has recently become operational, increasing the complexity of the network connectivity. Both Internet and local routing algorithms are showing the strain of continued growth. We have made several changes in the local routing algorithm to keep accommodating the current topology, and are participating in the development of new routing algorithms and protocols.
Recent work in collaboration with Van Jacobson of the Lawrence Berkeley Laboratory has led to the design and implementation of several new algorithms for TCP that improve throughput on both local and long-haul networks while reducing unnecessary retransmission. The improvement is especially striking when connections must traverse slow and/or lossy networks. The new algorithms include ``slow-start,'' a technique for opening the TCP flow control window slowly and using the returning stream of acknowledgements as a clock to drive the connection at the highest speed tolerated by the intervening network. A modification of this technique allows the sender to dynamically modify the send window size to adjust to changing network conditions. In addition, the round-trip timer has been modified to estimate the variance in round-trip time, thus allowing earlier retransmission of lost packets with less spurious retransmission due to increasing network delay. Along with a scheme proposed by Phil Karn of Bellcore, these changes reduce unnecessary retransmission over difficult paths such as Satnet by nearly two orders of magnitude while improving throughput dramatically.
The current TCP implementation is now being readied for more widespread distribution via the network. We will continue to refine the TCP and IP implementations during the term covered by this proposal, using the ARPANET, BARRNet, the NSF network and local campus nets as testbeds, in preparation for the next 4BSD release. In addition, we will incorporate applicable algorithms from this work into the TP-4 protocol implementation. Toward a Compatible File System Interface
The most critical shortcoming of our current UNIX system is in the area of distributed file systems. As with networking protocols, there is no single distributed file system that provides enough speed and functionality for all problems. It is frequently necessary to support several different remote file system protocols, just as it is necessary to run several different network protocols.
As network or remote file systems have been implemented for UNIX, several stylized interfaces between the file system implementation and the rest of the kernel have been developed. Among these are Sun Microsystems' Virtual File System interface (VFS) using vnodes [Sandburg85] [Kleiman86], Digital Equipment's Generic File System (GFS) architecture [Rodriguez86], AT&T's File System Switch (FSS) [Rifkin86], the LOCUS distributed file system [Walker85], and Masscomp's extended file system [Cole85]. Other remote file systems have been implemented in research or university groups for internal use- notably the network file system in the Eighth Edition UNIX system [Weinberger84] and two different file systems used at Carnegie Mellon University [Satyanarayanan85]. Numerous other remote file access methods have been devised for use within individual UNIX processes, many of them by modifications to the C I/O library similar to those in the Newcastle Connection [Brownbridge82].
Each design attempts to isolate file system-dependent details below a generic interface and to provide a framework within which new file systems may be incorporated. However, each of these interfaces is different from and is incompatible with the others. Each addresses somewhat different design goals, having been based on a different starting version of UNIX, having targeted a different set of file systems with varying characteristics, and having selected a different set of file system primitive operations.
Our work is aimed at providing a common framework to support these different distributed file systems simultaneously rather than to simply implement yet another protocol. This requires a detailed study of the existing protocols, and discussion with their implementors to determine whether they can modify their implementation to fit within our proposed framework. We have studied the various file system interfaces to determine their generality, completeness, robustness, efficiency, and aesthetics. Based on this study, we have developed a proposal for a new file system interface that we believe includes the best features of each of the existing implementations. This proposal and the rationale underlying its development have been presented to major software vendors as an early step toward convergence on a compatible file system interface. Briefly, the proposal adopts the 4.3BSD calling convention for file name lookup but otherwise is closely related to Sun's VFS [Karels86].
A prototype implementation is now being developed. We expect that this work will be finished in time for a release at the end of the period covered by this proposal. Work since the release of 4.3BSD
There have been several changes in the system since the release of 4.3BSD that have already been completed and would be part of any future release. The largest change has been the incorporation of support for the first non-VAX processor, the CCI Power 6/32. The Power 6 version of 4.3BSD is based on the compilers and device drivers done for CCI's 4.2BSD UNIX, and is otherwise similar to the VAX release of 4.3. The kernel source tree and the sources for all user-level software have been merged using a structure that will accommodate addition of other processor families. The 4.3BSD release for the CCI Power 6 (and for OEM versions sold by Harris and Sperry) is now in beta test.
During the work on the CCI machine, we resolved that disk geometry and filesystem layout information must be stored on each disk in a pack label. Disk labels were implemented for the CCI disks and for the most common types of disk controllers on the VAX. A utility was written to create and maintain the disk information, and other user-level programs that use such information now obtain it from the disk label. The use of this facility has allowed improvements in the file system's knowledge of irregular disk geometries such as track-to-track skew.
In recent months we have been heavily involved in the development the IEEE P1003.1 POSIX standard for portable operating system interfaces. We have participated actively in the incorporation and improvement of the job control and signal facilities first developed in Berkeley UNIX systems. Part of the current work has involved developing prototypes of the new interfaces to get feedback on their strengths and weaknesses. We expect that we will be able to provide POSIX compliant interfaces in Berkeley UNIX shortly after the standard is finalized. The major areas that we have prototyped include the POSIX terminal driver, POSIX job control, and POSIX group and user identifier semantics.
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