User-level network interface protocols

Powerful commodity systems and networks offer a promising direction for high performance computing because they are inexpensive and they closely track technology progress. However, high, raw-hardware performance is rarely delivered to the end user. Previous work has shown that the bottleneck in these architectures is the overheads imposed by the software communication layer. To reduce these overheads, researchers have proposed a number of user-space communication models. The common feature of these models is that applications have direct access to the network, bypassing the operating system in the common case and thus avoiding the cost of send/receive system calls. In this paper we examine five user-space communication layers, that represent different points in the configuration space: Generic AM, BIP-0.92, FM-2.02, PM-1.2, and VMMC-2. Although these systems support different communication paradigms and employ a variety of different implementation tradeoffs, we are able to quantitatively compare them on a single testbed consisting of a cluster of high-end PCs connected by a Myrinet network. We find that all five communication systems have very low latency for small messages, in the range of 5 to 17 s. Not surprisingly, this range is strongly influenced by the functionality offered by each system. We are encouraged, however, to find that features such as protected and reliable communication at user level and multiprogramming can be provided at very low cost. Bandwidth, however, depends primarily on how data is transferred between host memory and the network. Most of the investigated libraries support zero-copy protocols for certain types of data transfers, but differ significantly in the bandwidth delivered to end users. The highest bandwidth, between 95 and 125 MBytes/s for long message transfers, is delivered by libraries that use DMA on both send and receive sides and avoid all data copies. Libraries that perform additional data copies or use programmed I/O to send data to the network achieve lower maximum bandwidth, in the range of 60-70 MBytes/s.

An optical customer premises network (CPN), called H-Bus, designed to interface future broadband ISDN signals and distribute available bandwidth to terminal equipment connected to the CPN, is discussed. Key features of this network are the use of optical fiber as a transmission medium and a hybrid architecture, namely, a broadcast bus for the downstream (network interface to subscriber terminal) and a looped bus for the upstream (subscriber terminal to network interface) traffic. The physical layer of the network makes use of the synchronous optical network (SONET) transmission format. The user information is carried using the asynchronous transfer mode (ATM) technique. The reliability of H-Bus is improved through the use of a network component called an optical protection socket (OPS). This is an automatic optical bypass switch that protects the CPN in the case of individual node failures. To resolve any access contention on the upstream bus, a multipriority media access control protocol has been defined. Its performance is compared with that of protocols used in other high-speed local area networks.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Network equipment vendors are increasingly incorporating a programmable microprocessor on network interfaces to meet the performance and functionality requirements of present and emerging applications in parallel with market demand. This study identifies some properties of programmable network interface (PNI) workloads and their execution characteristics on modern high-performance microprocessor architectures including aggressive superscalar, fine-grain multithreaded, and simultaneous multithreaded architectures.

Recent advances in commodity network interface technology enable scientists and engineers to build clusters of workstations or PCs to execute parallel applications. However, raw-hardware network performance is rarely delivered to applications because of the overheads of communication software and operating systems. To reduce these overheads, a technique called user-level communication can be used to allow applications to access the network interface directly without intervention from the operating system. We examine two user-level communication systems, GM and BIP, on alpha based systems connected by a Myrinet network. In addition quantitative studies on how DMA initiation costs, flow control and reliable communication will effect the performance of communication software are presented.

Zero-copy means on any network node, during message transmission, there is no data copy among memory segments and all messages transmission are operated directly between user application space and outside of network through network interfaces. By DMA technology, network interface devices can store data packets into the address where it can be accessed directly by user application, the data packets copy operation is removed in kernel and reducing the data transmission path. By working together with TOE technology, it can drop the communication delay effectively and save a lot of CPU cost. In this paper, we based on Linux (kernel version 2.6.11), by modifying its network device driver snull.c (attached in Linux Device Driver version 3), to implement the memory mapping between Linux kernel space to user application space. The main method we used is the combination of MMAP and PROC procedures, and at the end, we also introduce the implementation of test program and the test strategies. The test results show us that the applications can access the applied memory of kernel by mapping

Network interfaces for programmable NICs and multicore platforms

User-level communication alleviates the software overhead of the communication subsystem by allowing applications to access the network interface directly. For that purpose, efficient address translation of virtual address to physical address is critical. In this study, we propose a system call based address translation scheme where every translation is done by the kernel instead of a translation cache on a network interface controller as in the previous cache based address translation. According to our experiments, our scheme achieves up to 4.5 % reduction in application execution time compared to the previous cache based approach

Cluster platforms offer good computational performance, but they still cannot utilize the potential of Gbit/s communication technology. While the speed of the Ethernet has grown to 1 Gbit/s, the functionality and the architectural support in the network interfaces has remained the same for more than a decade, so that the memory system becomes a limiting factor. To sustain the raw network speed in applications, a network interface architecture would be required, but, for all widely used stacks, a last copy is required for the (de)fragmentation of the transferred network packets, since Ethernet packets are smaller than a page size. Correctly defragmenting packets of various communication protocols in hardware is an extremely complex task. We therefore consider a speculative defragmentation technique that can eliminate the last defragmenting copy operation in zero-copy TCP/IP stacks on existing hardware. The payload of fragmented packets is separated from the headers and stored in a memory page that can be mapped directly to its final destination in user memory. To evaluate our ideas, we integrated a network interface driver with speculative defragmentation into an existing protocol stack and added well-known page remapping and fast buffer strategies. Measurements indicate that we can improve the performance for a Gigabit Ethernet over a standard Linux 2.2 TCP/IP stack by a factor of 1.5-2 for uninterrupted burst transfers. Furthermore, our study demonstrates good speculation success rates for a database and a scientific application code on a cluster of PCs.

The overhead of copying data through the central processor by a message passing protocol limits data transfer bandwidth. If the network interface directly transfers the user's memory to the network by issuing DMA, such data copies may be eliminated. Since the DMA facility accesses the physical memory address space, user virtual memory must be pinned down to a physical memory location before the message is sent or received. If each message transfer involves pin-down and release kernel primitives, message transfer bandwidth will decrease since those primitives are quite expensive. The authors propose a zero copy message transfer with a pin-down cache technique which reuses the pinned-down area to decrease the number of calls to pin-down and release primitives. The proposed facility has been implemented in the PM low-level communication library on the RWC PC Cluster II, consisting of 64 Pentium Pro 200 MHz CPUs connected by a Myricom Myrinet network, and running NetBSD. The PM achieves 108.8 MBytes/sec for a 100% pin-down cache hit ratio and 78.7 MBytes/sec for all pin-down cache miss. The MPI library has been implemented on top of PM. According to the NAS parallel benchmarks result, an application is still better performance in case that cache miss ratio is very high.

Redundant data transmission in control/estimation over lossy networks

Recently, NAND flash memory has emerged as a next generation storage device because it has several advantages, such as low power consumption, shock resistance, and so on. However, it is necessary to use a flash translation layer (FTL) to intermediate between NAND flash memory and conventional file systems because of the unique hardware characteristics of flash memory. This paper proposes a new clustered FTL (CFTL) that uses clustered hash tables and a two-level software cache technique. The CFTL can anticipate consecutive addresses from the host because the clustered hash table uses the locality of reference in a large address space. It also adaptively switches logical addresses to physical addresses in the flash memory by using block mapping, page mapping, and a two-level software cache technique. Furthermore, anticipatory I/O management using continuity counters and a prefetch scheme enables fast address translation. Experimental results show that the proposed address translation mechanism for CFTL provides better performance in address translation and memory space usage than the well-known NAND FTL (NFTL) and adaptive FTL (AFTL).

Summary form only given. Capacity, reliability, and delay are three magic words used for describing concepts of computer network design. While capacity and delay are relatively well understood, this is not the case for reliability. The term reliability is often used interchangeably with availability and dependability. Increased redundancy in the network structure is often considered as an important, or even the only, way to achieve higher levels of reliability. The tutorial presents the role of reliability (in a broad sense) in network design. Factors affecting performability of the communications system are discussed. Reliability in the network design process, in the context of a systems approach to network design, is considered in more detail. Examples of calculations of reliability figures for different network designs are considered using the Delite tool. Reliability support in communications protocols is discussed. Examples of simulations and animations of network dynamics are presented using the ns-2 and nam tools

Nowadays, vehicles are not only merely used as a transportation medium, but also as a highly mobile Internet of Things (IoT) node, collecting data from all types of sources. The delivery of aggregated vehicle sensor data into the cloud for further analysis is very fragile, as vehicles move fast in their environment and channel conditions vary heavily. Next to mastering possible packet loss, communication protocols need to quickly adapt to the frequent data rate changes. Random Linear Network Coding (RLNC) has been proven as an efficient and robust mechanism for reliable data transfer especially on lossy channels. In this paper, the authors extend the Scalable Network Coding (ScalaNC) framework with the novel congestion control Bottleneck, Bandwidth and Round-Trip Time (BBR) in order to quickly adapt to the frequent changes in data rate and allow effective transfer of high amounts of data from vehicles and into the cloud. ScalaNC is validated in a Hardware-in-the-Loop field test consisting of a Long Term Evolution (LTE) base station and channel emulator.

Open-source, Decentralized Online Social Networks (DOSNs) are emerging as alternatives to the popular yet centralized and profit-driven platforms like Facebook or Twitter. In DOSNs, users can set up their own server, or instance, while they can actually interact with users of other instances. Moreover, by adopting the same communication protocol, DOSNs become part of a massive social network, namely the Fediverse. Mastodon is the most relevant platform in the Fediverse to date, and also the one that has attracted attention from the research community. Existing studies are however limited to an analysis of a relatively outdated sample of Mastodon focusing on few aspects at a user level, while several open questions have not been answered yet, especially at the instance level. In this work, we aim at pushing forward our understanding of the Fediverse by leveraging the primary role of Mastodon therein. Our first contribution is the building of an up-to-date and highly representative dataset of Mastodon. Upon this new data, we have defined a network model over Mastodon instances and exploited it to investigate three major aspects: the structural features of the Mastodon network of instances from a macroscopic as well as a mesoscopic perspective, to unveil the distinguishing traits of the underlying federative mechanism; the backbone of the network, to discover the essential interrelations between the instances; and the growth of Mastodon, to understand how the shape of the instance network has evolved during the last few years, also when broading the scope to account for instances belonging to other platforms. Our extensive analysis of the above aspects has provided a number of findings that reveal distinguishing features of Mastodon and that can be used as a starting point for the discovery of all the DOSN Fediverse.

Open-source, Decentralized Online Social Networks (DOSNs) are emerging as alternatives to the popular yet centralized and profit-driven platforms like Facebook or Twitter. In DOSNs, users can set up their own server, or instance, while they can actually interact with users of other instances. Moreover, by adopting the same communication protocol, DOSNs become part of a massive social network, namely the Fediverse. Mastodon is the most relevant platform in the Fediverse to date, and also the one that has attracted attention from the research community. Existing studies are however limited to an analysis of a relatively outdated sample of Mastodon focusing on few aspects at a user level, while several open questions have not been answered yet, especially at the instance level. In this work, we aim at pushing forward our understanding of the Fediverse by leveraging the primary role of Mastodon therein. Our first contribution is the building of an up-to-date and highly representative dataset of Mastodon. Upon this new data, we have defined a network model over Mastodon instances and exploited it to investigate three major aspects: the structural features of the Mastodon network of instances from a macroscopic as well as a mesoscopic perspective, to unveil the distinguishing traits of the underlying federative mechanism; the backbone of the network, to discover the essential interrelations between the instances; and the growth of Mastodon, to understand how the shape of the instance network has evolved during the last few years, also when broading the scope to account for instances belonging to other platforms. Our extensive analysis of the above aspects has provided a number of findings that reveal distinguishing features of Mastodon and that can be used as a starting point for the discovery of all the DOSN Fediverse.