This paper describes a new operating system kernel, called the x-kernel, that provides an explicit architecture for constructing and composing network protocols. Our experience implementing and evaluating several protocols in the x-kernel shows that this architecture is both general enough to accommodate a wide range of protocols, yet efficient enough to perform competitively with less structured operating systems. 1 Introduction Network software is at the heart of any distributed system. It manages the communication hardware that connects the processors in the system and it defines abstractions through which processes running on those processors exchange messages. Network software is extremely complex: it must hide the details of the underlying hardware, recover from transmission failures, ensure that messages are delivered to the application processes in the appropriate order, and manage the encoding and decoding of data. To help manage this complexity, network software is divi...

Traditionally, network software hasbeen structured in a monolithic fashion with all protocol stacks executing either within the kernel or in a single trusted user-level server. This organization is motivated by performance and security concerns. However, considerations of code maintenance, ease of debugging, customization, and the simultaneous existence of multiple protocols argue for separating the implementations into more manageable user-level libraries of protocols. This paper describes the design and implementation of transport protocols as user-level libraries. We begin by motivating the need for protocol implementations as user-level libraries and placing our approachin the context of previous work. We then describe our alternative to monolithic protocol organization, which has been implemented on Mach workstations connected not only to traditional Ethernet, but also to a more modern network, the DEC SRC AN1. Based on our experience, we discuss the implications for host-network ...

We present detailed measurements of various processing overheads of the TCP/IP and UDP/IP protocol stacks on a DECstation 5000/200 running the Ultrix 4.2a operating system. These overheads include data-touching operations, such as the checksum computation and data movemen ~ which are well known to be major time consumers. In this stud y, we also considered overheads due to non-data touching operations, such as network buffer manipulation, protocol-specific processing, operating system functions, data structure manipulations (other than network buffers), and error checking. We show that when one considers realistic message size dktributions, where the majority of messages are small, the cumulative time consumed by the nondata touching overheads represents the majority of processing time. We assert that it will be difficult to significantly reduce the cumulative processing time due to non-data touching overheads. The goal of this study is to determine the relative importance of various processing overheads in network software, in particular, the TCP/IP and UDPAP protocol stacks. In the prrsg significant focus has been placed on maximizing throughput noting that “data

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Modern switched networks such as ATM and Myrinet enable low-latency, high-bandwidth communication. This performance has not been realized by current applications, because of the high processing overheads imposed by existing communications software. These overheads are usually not hidden with large packets; most network traffic is small. We have developed Fast Sockets, a local-area communication layer that utilizes a high-performance protocol and exports the Berkeley Sockets programming interface. Fast Sockets realizes round-trip transfer times of 60 microseconds and maximum transfer bandwidth of 33 MB/second between two UltraSPARC 1s connected by a Myrinet network. Fast Sockets obtains performance by collapsing protocol layers, using simple buffer management strategies, and utilizing knowledge of packet destinations for direct transfer into user buffers. Using receive posting, we make the Sockets API a single-copy communications layer and enable regular Sockets programs to exploit the performance of modern networks. Fast Sockets transparently reverts to standard TCP/IP protocols for wide-area communication.

: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 15 CHAPTER 1: INTRODUCTION : : : : : : : : : : : : : : : : : : : : : : : : : : 17 1.1 Introduction to Network Software : : : : : : : : : : : : : : : : : : : : : 17 1.2 Network Software is Evolving : : : : : : : : : : : : : : : : : : : : : : : 20 1.3 Existing Support for Network Software Development : : : : : : : : : : : 21 1.3.1 Protocol Frameworks : : : : : : : : : : : : : : : : : : : : : : 21 1.3.2 Formal Techniques : : : : : : : : : : : : : : : : : : : : : : : : 22 1.4 New Strategies for Supporting Protocol Development : : : : : : : : : : : 23 1.4.1 Simplifying Protocol Development by Imposing Constraints : : 24 1.4.2 Language Support for Protocol Development : : : : : : : : : : 25 1.5 Morpheus : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 26 1.5.1 Abstraction : : : : : : : : : : : : : : : : : : : : : : : : : : : : 26 1.5.2 Modularity : : : : : : : : : : : : : : : : : : : : : : : : : : : : ...

This paper presents detailed measurements of processing overheads for the Ultrix 4.2a implementation of TCP/IP network software running on a DECstation 5000/200. The performance results were used to unco ver throughput and latency bottlenecks. We present a scheme for impro ving throughput when sending large messages by avoiding most checksum computations in a relatively safe manner. We also show that for the implementation we studied, reducing latency (when sending small messages) is a more dif ficult problem because processing overheads are spread over many operations; gaining a significant savings would require the optimization of many different mechanisms. This is especially important because, when processing a realistic workload, we ha ve found that non-data-touching operations

This paper describes the design and evaluates the performance of the DASH MP system, with an emphasis on its use of remapping. In addition, we study the system performance at a `microscopic' level by breaking down a user-level MP operation into short segments and measuring their individual performance. The results are used to evaluate and refine our design decisions

Providing end-to-end gigabit communication support for high-bandwidth multimedia applications requires transport systems that transfer data efficiently via network protocols such as TCP, TP4, XTP, and STII. This paper describes and classifies transport system services that integrate operating system resources such as CPU(s), virtual memory, and I/O devices together with network protocols to support distributed multimedia applications running on local and wide area networks. A taxonomy is presented that compares and evaluates four commercial and experimental transport systems in terms of their protocol processing support. The systems covered in this paper include System V UNIX STREAMS, the BSD UNIX networking subsystem, the x-kernel, and the Choices Conduit system. This paper is intended to navigate researchers and developers through the transport system design space by describing alternative approaches for key transport system services. 1 Introduction Transport systems integ...

Networking software is a growing bottleneck in modern workstations, particularly for high throughput applications such as networked digital video. We measure various components of the UDP/IP protocol stack in a DECstation 5000/200 running Ultrix 4.2a, and find that checksumming and copying dominate the processing time for high throughput applications. This paper describes network software measurements and performance improvements which derive from a faster checksum implementation.