Don't mind the gap: Bridging network-wide objectives and device-level configurations

We reflect on the historical context that lead to Propane, a high-level language and compiler to help network operators bridge the gap between network-wide routing objectives and low-level configurations of devices that run complex, distributed protocols. We also highlight the primary contributions that Propane made to the networking literature and describe ongoing challenges. We conclude with an important lesson learned from the experience

Equation-Based Congestion Control for Unicast Applications: the Extended Version

This paper proposes a mechanism for equation-based congestion control for unicast traffic. Most best-effort traffic in the current Internet is well-served by the dominant transport protocol TCP. However, traffic such as best-effort unicast streaming multimedia could find use for a TCP-friendly congestion control mechanism that refrains from reducing the sending rate in half in response to a single packet drop. With our mechanism, the sender explicitly adjusts its sending rate as a function of the measured rate of loss events, where a loss event consists of one or more packets dropped within a single round-trip time. We use both simulations and experiments over the Internet to explore performance. Equation-based congestion control is also a promising avenue of development for congestion control of multicast traffic, and so an additional reason for this work is to lay a sound basis for the later development of multicast congestion control

Opportunistic Use of Client Repeaters to Improve Performance of WLANs

Currently deployed IEEE 802.11WLANs (Wi-Fi networks) share access point (AP) bandwidth on a per-packet basis. However, the various stations communicating with the AP often have different signal qualities, resulting in different transmission rates. This induces a phenomenon known as the rate anomaly problem, in which stations with lower signal quality transmit at lower rates and consume a significant majority of airtime, thereby dramatically reducing the throughput of stations transmitting at high rates. We propose a practical, deployable system, called SoftRepeater, in which stations cooperatively address the rate anomaly problem. Specifically, higher-rate Wi-Fi stations opportunistically transform themselves into repeaters for stations with low data-rates when transmitting to/from the AP. The key challenge is to determine when it is beneficial to enable the repeater functionality. In this paper, we propose an initiation protocol that ensures that repeater functionality is enabled only when appropriate. Also, our system can run directly on top of today's 802.11 infrastructure networks. We also describe a novel, zero-overhead network coding scheme that further alleviates undesirable symptoms of the rate anomaly problem. We evaluate our system using simulation and testbed implementation, and find that SoftRepeater can improve cumulative throughput by up to 200%

RDMA over Commodity Ethernet at Scale

ABSTRACT Over the past one and half years, we have been using RDMA over commodity Ethernet (RoCEv2) to support some of Microsoft's highly-reliable, latency-sensitive services. This paper describes the challenges we encountered during the process and the solutions we devised to address them. In order to scale RoCEv2 beyond VLAN, we have designed a DSCP-based priority flow-control (PFC) mechanism to ensure large-scale deployment. We have addressed the safety challenges brought by PFCinduced deadlock (yes, it happened!), RDMA transport livelock, and the NIC PFC pause frame storm problem. We have also built the monitoring and management systems to make sure RDMA works as expected. Our experiences show that the safety and scalability issues of running RoCEv2 at scale can all be addressed, and RDMA can replace TCP for intra data center communications and achieve low latency, low CPU overhead, and high throughput

Model-based approach to TCP-friendly congestion control

Continuous media (CM) applications such as streaming audio and video are being rapidly deployed throughout the Internet. These applications must be able to co-exist with each other and with traditional TCP-based applications. One requirement for such co-existence is the implementation of congestion control mechanism by CM applications. TCP-based applications reduce their sending rate in face of network congestion. Many CM applications run on top of UDP, as TCP\u27s error control mechanisms are ill suited for CM applications. UDP-based applications must provide their own congestion control. In this dissertation, we work towards development of a congestion control protocol for CM applications that will facilitate co-existence of CM applications with each other, and with TCP flows. We address this problem in two steps. First, we develop an analytical model of TCP. Such a model is essential to understand TCP\u27s congestion control behavior under a variety of network conditions. Our model provides a closed form equation that can be used to calculate the send rate of a TCP connection, given the packet loss rate, the round trip time and the base timeout value. We verify the accuracy of our model against measurements taken in the Internet. The next step is to develop a congestion control protocol that is suitable for the CM applications and also shares the bandwidth fairly with TCP connections that travel over the same network path. We develop a protocol that uses our TCP model as the control function of a feedback loop. The protocol design is deliberately kept simple to allow us to evaluate the feasibility of the model-based approach to congestion control. The simple protocol is evaluated using simulations and Internet experiments. Our results show that the protocol performs well under a variety of network conditions. We then refine the simple protocol, trading off design simplicity to achieve better performance. We introduce sophisticated mechanisms to track packet loss rate, control rate increase and handle startup behavior. We evaluate the protocol using simulations and Internet experiments. Our results show that the more complex protocol provides a smooth sending rate and is TCP-friendly under a wide variety of networking conditions

An empirical study of client interactions with a continuous-media courseware server

While considerable research has gone into investigating various networking and operating system mechanisms for supporting the transfer and playout of stored continuous media (e.g., audio and video), very little information is available about how users actually use such systems. Understanding how users interact with such a system -- i.e., developing a user workload characterization -- is crucial in designing and evaluating efficient continuous media (CM) resource allocation and access mechanisms. We have designed and built an interactive WWW-based, multimedia, client/server application, known as MANIC (Multimedia Asynchronous Networked Individualized Courseware), that streams synchronized CM (currently audio) and HTML documents to remote users. MANIC was used by more than 200 users during the Spring 1997 semester to listen to, and view, the stored audio lectures and lecture notes for a full-semester senior-level course at the University of Massachusetts. In this paper we pr..