Temporal behavior of Ethernet communications: impact of the operating system and protocol stack

Ethernet is currently the most widely used networking technology, spanning across many application domains including embedded systems. In this particular case, Ethernet is even used in many time-critical applications in which the delay induced by communication must be short and bounded. It is thus very important to understand the entire transmission process and assess its temporal behavior. There are a number of aspects to consider, including the network protocol, network topology, network elements and end devices. This paper aims at assessing the impact of the operating system and its protocol stack implementation in the end devices on the network temporal behavior. We studied four operating systems, namely a standard Ubuntu distribution with and without a real-time kernel patch, an embedded stripped down version of Linux and QNX Neutrino, and two hardware platforms, namely ordinary PCs and a single board computer based on an AVR32 CPU. We measured the Round Trip Delay (RTD) using RAW, UDP and TCP sockets to interface the protocol stack. We verified that on high computing power platforms the difference between the sockets is small but still significant in resource-constrained platforms. On the other hand, full featured general OSs present rather large worst-case delays. These can be reduced using real-time patches for those OSs, RTOSs, or even removing unnecessary modules, services and particularly, data intensive device drivers. We believe this study can be helpful for system designers as well as for teaching networks courses in embedded systems.Ethernet is currently the most widely used networking technology, spanning across many application domains including embedded systems. In this particular case, Ethernet is even used in many time-critical applications in which the delay induced by communication must be short and bounded. It is thus very important to understand the entire transmission process and assess its temporal behavior. There are a number of aspects to consider, including the network protocol, network topology, network elements and end devices. This paper aims at assessing the impact of the operating system and its protocol stack implementation in the end devices on the network temporal behavior. We studied four operating systems, namely a standard Ubuntu distribution with and without a real-time kernel patch, an embedded stripped down version of Linux and QNX Neutrino, and two hardware platforms, namely ordinary PCs and a single board computer based on an AVR32 CPU. We measured the Round Trip Delay (RTD) using RAW, UDP and TCP sockets to interface the protocol stack. We verified that on high computing power platforms the difference between the sockets is small but still significant in resource-constrained platforms. On the other hand, full featured general OSs present rather large worst-case delays. These can be reduced using real-time patches for those OSs, RTOSs, or even removing unnecessary modules, services and particularly, data intensive device drivers. We believe this study can be helpful for system designers as well as for teaching networks courses in embedded systems

A USER-LEVEL SOCKET LAYER OVER MULTIPLE PHYSICAL NETWORK INTERFACES Abstract

In this paper, we describe the design and implementation of an UDP-based socket that utilizes multiple network interface units connected through one or more networks. network APIs to hide low-level technical details from users. Parallel message fragmentation and reconstruction techniques and a reliable UDP-based protocol are introduced. The proposed socket layer transparently provides an expandable high bandwidth solution, fault tolerance, and load balancing for transmitting large messages over multiple networks. A prototype socket based on this model, called MuniSocket (Multiple Network Interface Socket), has been implemented and evaluated

Concurrent multipath transmission to improve performance for multi-homed devices in heterogeneous networks

Recent network technology developments have led to the emergence of a variety of access network technologies - such as IEEE 802.11, wireless local area network (WLAN), IEEE 802.16, Worldwide Interoperability for Microwave Access (WIMAX) and Long Term Evolution (LTE) - which can be integrated to offer ubiquitous access in a heterogeneous network environment. User devices also come equipped with multiple network interfaces to connect to the different network technologies, making it possible to establish multiple network paths between end hosts. However, the current connectivity settings confine the user devices to using a single network path at a time, leading to low utilization of the resources in a heterogeneous network and poor performance for demanding applications, such as high definition video streaming. The simultaneous use of multiple network interfaces, also called bandwidth aggregation, can increase application throughput and reduce the packets' end-to-end delays. However, multiple independent paths often have heterogeneous characteristics in terms of offered bandwidth, latency and loss rate, making it challenging to achieve efficient bandwidth aggregation. For instance, striping the flow's packets over multiple network paths with different latencies can cause packet reordering, which can significantly degrade performance of the current transport protocols. This thesis proposes three new solutions to mitigate the effects of network path heterogeneity on the performance of various concurrent multipath transmission settings. First, a network layer solution is proposed to stripe packets of delay-sensitive and high-bandwidth applications for concurrent transmission across multiple network paths. The solution leverages the paths' latency heterogeneity to reduce packet reordering, leading to minimal reordering delay, which improves performance of delay-sensitive applications. Second, multipath video streaming is developed for H.264 scalable video, where the reference video packets are adaptively assigned to low loss network paths to reduce drifting errors, thus combatting H.264 video distortion effectively. Finally, a new segment scheduling framework - which carefully considers path heterogeneity - is incorporated into the IETF Multipath TCP to improve throughput performance. The proposed solutions have been validated using a series of simulation experiments. The results reveal that the proposed solutions can enable efficient bandwidth aggregation for concurrent multipath transmission over heterogeneous network paths