In everyday meetings, automatic association of co-located mobile devices would ease sharing of web-links, media, and other information. We propose a method that compares patterns of silence from device microphones to detect co-location of those devices. This method works with unsynchronized audio capture, requires only 100bps and preserves privacy. We show how to formulate pattern matching in a sequential hypothesis framework so that changes in co-location status (when people leave or join a meeting) can be determined promptly, and how to compute the likelihood ratio in practice. Using 16 hours of captured audio, we show that our approach can correctly determine device co-location with a low error rate of 0.05%, and can detect co-location changes 10 seconds faster than a similar decision rule based on a constant time window. Compared to a prior audio signature method, we achieve higher accuracy at 1/7 the bit rate.

This document describes the technology behind the accompanying video, which gives a demonstration of determining the dynamic group membership of a meeting by matching patterns of relative audio silence, or "silence signatures," sensed by mobile devices.

A list of the dynamically changing group membership of a meeting supports a variety of meeting-related activities. Effortless content sharing might be the most important application, but we can also use it to provide business card information for attendees, feed information into calendar applications to simplify scheduling of follow-up meetings, populate the membership of collaborative editing applications, mailing lists, and social networks, and perform many other tasks.

As our national mathematics and science scores continue to fall below expectations, creating environments that engage the professional scientific and engineering communities in public education becomes increasingly important. Most mathematics and science teachers in high schools do not have a professional background in mathematics, science, or engineering (STEM) fields; thus, students in the public education system rarely interact with STEM professionals, and know little about the opportunities for careers in these fields. The NSF GK12 program supports graduate students who spend time in K12 classrooms for the purposes of learning to share their research with a nontechnical community. In year 3 of this specific GK12 program, a distance component was implemented by placing the graduate student in the classroom, virtually, through online streaming video. This paper discusses the technology, both hardware and software, that is used in this arrangement, as well as the challenges associated with implementing the technology in the school. This paper also describes the approach taken in designing and deploying an interdisciplinary learning module via distance. Finally, the paper describes the plans for continued distance components of the program.

Desktop video conferencing participants are often poorly positioned in their outgoing video - unaware of their appearance on camera. We combine face detection, feature tracking and motion detection for automatic real-time detection of poorly framed participants and subsequently provide framing feedback by compositing their incoming and outgoing video streams. Our solution provides participants visual feedback only while they have framing problems. Otherwise the display shows only the remote participants, allowing users to focus fully on the conference. We analyze the system components and describe a user study that found advantages of our approach over the existing mirror window solution.

No abstract available.

Emerging Web services, such as email, photo sharing, and web site archives, must preserve large volumes of quickly accessible data indefinitely into the future. The costs of doing so often determine whether the service is economically viable. We make the case that these applications' demands on large scale storage systems over long time horizons require us to reevaluate traditional system designs. We examine threats to long-lived data from an end-to-end perspective, taking into account not just hardware and software faults but also faults due to humans and organizations. We present a simple model of long-term storage failures that helps us reason about various strategies for addressing some of these threats. Using this model we show that the most important strategies for increasing the reliability of long-term storage are detecting latent faults quickly, automating fault repair to make it cheaper and faster, and increasing the independence of data replicas.

The LOCKSS project has developed and deployed in a world-wide test a peer-to-peer system for preserving access to journals and other archival information published on the Web. It consists of a large number of independent, low-cost, persistent Web caches that cooperate to detect and repair damage to their content by voting in “opinion polls.” Based on this experience, we present a design for and simulations of a novel protocol for voting in systems of this kind. It incorporates rate limitation and intrusion detection to ensure that even some very powerful adversaries attacking over many years have only a small probability of causing irrecoverable damage before being detected.

We study the behavior of the new MAC protocols for QoS in the proposed IEEE 802.11e draft standard and analyze them for their ability to fulfill their goals of better QoS and higher channel efficiency. We study the response of these mechanisms to various choices in available protocol parameters. We show that HCF reduces channel contention and allows better channel utilization. However, both the proposed MAC coordination functions, EDCF and HCF, are highly sensitive to protocol parameters. We believe that the effectiveness of these functions also depends on the scheduling algorithms. The effects of the various policy choices need to be understood and validated before the draft becomes a standard.

The LOCKSS project has developed and deployed in a world-wide test a peer-to-peer system for preserving access to journals and other archival information published on the Web. It consists of a large number of independent, low-cost, persistent web caches that cooperate to detect and repair damage to their content by voting in "opinion polls." Based on this experience, we present a design for and simulations of a novel protocol for voting in systems of this kind. It incorporates rate limitation and intrusion detection to ensure that even some very powerful adversaries attacking over many years have only a small probability of causing irrecoverable damage before being detected.

This paper describes two techniques that improve throughput in an ad hoc network in the presence of nodes that agree to forward packets but fail to do so. To mitigate this problem, we propose categorizing nodes based upon their dynamically measured behavior. We use a watchdog that identifies misbehaving nodes and a pathrater that helps routing protocols avoid these nodes. Through simulation we evaluate watchdog and pathrater using packet throughput, percentage of overhead (routing) transmissions, and the accuracy of misbehaving node detection. When used together in a network with moderate mobility, the two techniques increase throughput by 17% in the presence of 40% misbehaving nodes, while increasing the percentage of overhead transmissions from the standard routing protocol's 9% to 17%. During extreme mobility, watchdog and pathrater can increase network throughput by 27%, while increasing the overhead transmissions from the standard routing protocol's 12% to 24%.

To understand better how users take advantage of wireless networks, we examine a twelve-week trace of a building-wide local-area wireless network. We analyze the network for overall user behavior (when and how intensively people use the network and how much they move around), overall network traffic and load characteristics (observed throughput and symmetry of incoming and outgoing traffic), and traffic characteristics from a user point of view (observed mix of applications and number of hosts connected to by users).

We describe a deterministic model of packet delay and use it to derive both the packet pair [2] property of FIFO-queueing networks and a new technique packet tailgating) for actively measuring link bandwidths. Compared to previously known techniques, packet tailgating usually consumes less network bandwidth, does not rely on consistent behavior of routers handling ICMP packets, and does not rely on timely delivery of acknowledgments.

We are facing a growing user demand for ubiquitous Internet access. As result, network ports and wireless LANs are becoming common in public spaces inside buildings such as lounges, conference rooms and lecture halls. This introduces the problem of protecting networks accessible through these public ports from unauthorized use. In this paper, we study the problem of access control through public network ports. We view this problem as a special case of the more general problem of access control for a service on a network. We present an access control model on which we base our solution. This model has three components: authentication, authorization, and access verification. We describe the design and implementation of a system that allows secure network access through public network ports and wireless LANs. The design requires no special hardware or custom client software, resulting in minimal deployment cost and maintenance overhead. The system has a user-friendly, Web-based interface, offers good security, and scales to a campus-sized community.

Accurate network bandwidth measurement is important to a variety of network applications. Unfortunately, accurate bandwidth measurement is difficult. We describe some current bandwidth measurement techniques: using throughput, and packet pair. We explain some of the problems with these techniques, including poor accuracy, poor scalability, lack of statistical robustness, poor agility in adapting to bandwidth changes, lack of flexibility in deployment, and inaccuracy when used on a variety of traffic types. The authors solutions to these problems include the use of a packet window to adapt quickly to bandwidth changes, receiver only packet pair to combine accuracy and ease of deployment, and potential bandwidth filtering to increase the accuracy. These techniques are at least as accurate as previously used filtering algorithms, and in some situations, they are more than 37% more accurate.

Article Analysis of a metropolitan-area wireless network Share on Authors: Diane Tang Stanford University, Gates 4A, Stanford Stanford University, Gates 4A, StanfordView Profile , Mary Baker Stanford University, Gates 4A, Stanford, CA Stanford University, Gates 4A, Stanford, CAView Profile Authors Info & Claims MobiCom '99: Proceedings of the 5th annual ACM/IEEE international conference on Mobile computing and networkingAugust 1999 Pages 13–23https://doi.org/10.1145/313451.313460Online:01 August 1999Publication History 75citation615DownloadsMetricsTotal Citations75Total Downloads615Last 12 Months10Last 6 weeks0 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteGet Access

Byte stuffing is a process that encodes a sequence of data bytes that may contain "illegal" or "reserved" values, using a potentially longer sequence that contains no occurrences of these values. The extra length is referred to here as the overhead of the encoding. To date, byte stuffing algorithms, such as those used by SLIP, PPP, and AX.25, have been designed to incur low average overhead, but little effort has been made to minimize their worst-case overhead. However, there are some increasingly popular network devices whose performance is determined more by the worst case than by the average case. For example, the transmission time for ISM-band packet radio transmitters is strictly limited by FCC regulation. To adhere to this regulation, the current practice is to set the maximum packet size artificially low so that no packet, even after worst-case overhead, can exceed the transmission time limit. This paper presents a new byte stuffing algorithm, called consistent overhead byte stuffing (COBS), which tightly bounds the worst-case overhead. It guarantees, in the worst case, to add no more than 1 byte in 254 to any packet. For large packets, this means that their encoded size is no more than 100.4% of their pre-encoding size. This is much better than the 200% worst-case bound that is common for many byte stuffing algorithms, and is close to the information-theoretic limit of about 100.07%. Furthermore, the COBS algorithm is computationally cheap, and its average overhead is very competitive with that of existing algorithms.

Fueled by the large number of powerful light-weight portable computers, the expanding availability of wireless networks, and the popularity of the Internet, there is an increasing demand to connect portable computers to the Internet at any time and in any place. However, the dynamic nature of such connectivity requires more flexible network support than has typically been available for stationary workstations. This paper introduces the following two mechanisms, in the context of Mobile IP [24], to ensure a mobile host's convenient and efficient communication with other hosts in a changing environment. One mechanism supports multiple packet delivery methods (such as regular IP or Mobile IP) and adaptively selects the most appropriate one to use according to the characteristics of each traffic flow. The other mechanism enables a mobile host to make use of multiple active network interfaces simultaneously and to control the selection of the most desirable network interfaces for both outgo...

Byte stuffing is a process that transforms a sequence of data bytes that may contain 'illegal' or 'reserved' values into a potentially longer sequence that contains no occurrences of those values. The extra length is referred to in this paper as the overhead of the algorithm.To date, byte stuffing algorithms, such as those used by SLIP [RFC1055], PPP [RFC1662] and AX.25 [ARRL84], have been designed to incur low average overhead but have made little effort to minimize worst case overhead.Some increasingly popular network devices, however, care more about the worst case. For example, the transmission time for ISM-band packet radio transmitters is strictly limited by FCC regulation. To adhere to this regulation, the practice is to set the maximum packet size artificially low so that no packet, even after worst case overhead, can exceed the transmission time limit.This paper presents a new byte stuffing algorithm, called Consistent Overhead Byte Stuffing (COBS), that tightly bounds the worst case overhead. It guarantees in the worst case to add no more than one byte in 254 to any packet. Furthermore, the algorithm is computationally cheap, and its average overhead is very competitive with that of existing algorithms.

Mobile IP protocols allow mobile hosts to send and receive packets addressed with their home network IP address, regardless of the IP address of their current point of attachment in the Internet.While some recent work in Mobile IP focuses on a couple of specific routing optimizations for sending packets to and from mobile hosts [Joh96] [Mon96], we show that a variety of different optimizations are appropriate in different circumstances. The best choice, which may vary on a connection-by-connection or even a packet-by-packet basis, depends on three factors: the characteristics the protocol should optimize, the permissiveness of the networks over which the packets travel and the level of mobile-awareness of the hosts with which the mobile host corresponds.Of the sixteen possible routing choices that we identify, we describe the seven that are most useful and discuss their benefits and limitations. These optimizations range from the most costly, which provides completely transparent mobility in all networks, to the most economical, which does not attempt to conceal location information. In particular, hosts should retain the option to communicate conventionally without using Mobile IP whenever appropriate.Further, we show that all optimizations can be described using a 4×4 grid of packet characteristics. This makes it easier for a mobile host, through a series of tests, to determine which of the currently available optimizations is the best to use for any given correspondent host.

Given the decreasing cost of non-volatile RAM (NVRAM), by the late 1990’s it will be feasible for most workstations to include a megabyte or more of NVRAM, enabling the design of higher-performance, more reliable systems. We present the trace-driven simulation and analysis of two uses of NVRAM to improve I/O performance in distributed file systems: non-volatile file caches on client workstations to reduce write traffic to file servers, and write buffers for write-optimized file systems to reduce server disk accesses. Our results show that a megabyte of NVRAM on diskless clients reduces the amount of file data written to the server by 40 to 50%. Increasing the amount of NVRAM shows rapidly diminishing returns, and the particular NVRAM block replacement policy makes little difference to write traffic. Closely integrating the NVRAM with the volatile cache provides the best total traffic reduction. At today’s prices, volatile memory provides a better performance improvement per dollar than NVRAM for client caching, but as volatile cache sizes increase and NVRAM becomes cheaper, NVRAM will become cost effective. On the server side, providing a one-half megabyte write-buffer per file system reduces disk accesses by about 20 % on most of the measured logstructured file systems (LFS), and by 90 % on one heavilyused file system that includes transaction-processing workloads. 1.

We analyzed the user-level file access patterns and caching behavior of the Sprite distributed file system. The first part of our analysis repeated a study done in 1985 of the: BSD UNIX file system. We found that file throughput has increased by a factor of 20 to an average of 8 Kbytes per second per active user over 10-minute intervals, and that the use of process migration for load sharing increased burst rates by another factor of six. Also, many more very large (multi-megabyte) files are in use today than in 1985. The second part of our analysis measured the behavior of Sprite's main-memory file caches. Client-level caches average about 7 Mbytes in size (about one-quarter to one-third of main memory) and filter out about 50% of the traffic between clients and servers. 35% of the remaining server traffic is caused by paging, even on workstations with large memories. We found that client cache consistency is needed to prevent stale data errors, but that it is not invoked often enough to degrade overall system performance.