Improving reliable transport and handoff performance in cellular wireless networks

TCP is a reliable transport protocol tuned to perform well in traditional networks where congestion is the primary cause of packet loss. However, networks with wireless links and mobile hosts incur significant losses due to bit-errors and handoffs. This environment violates many of the assumptions made by TCP, causing degraded end-to-end performance. In this paper, we describe the additions and modifications to the standard Internet protocol stack (TCP/IP) to improve end-to-end reliable transport performance in mobile environments. The protocol changes are made to network-layer software at the base station and mobile host, and preserve the end-to-end semantics of TCP. One part of the modifications, called the snoop module, caches packets at the base station and performs local retransmissions across the wireless link to alleviate the problems caused by high bit-error rates. The second part is a routing protocol that enables low-latency handoff to occur with negligible data loss. We have implemented this new protocol stack on a wireless testbed. Our experiments show that this system is significantly more robust at dealing with unreliable wireless links than normal TCP; we have achieved throughput speedups of up to 20 times over regular TCP and handoff latencies over 10 times shorter than other mobile routing protocols.This work was supported by ARPA Contract J-FBI-93-153. This paper was in part presented at the ACM Mobile Computing and Networking Conference (Mobicom '95), Berkeley, California, 14–15 November 1995.     

Gender schema theory and sex role inventories: Some conceptual and psychometric considerations.

Assessed whether the Bem Sex-Role Inventory (BSRI) and the Personality Research Form (PRF) ANDRO scale developed by J. I. Berzins et al (see record 1978-30742-001) are appropriate for investigations of gender schema theory, as outlined by S. L. Bem (see record 1981-25685-001). On the basis of the propositions of gender schema theory, several predictions were made about the psychometric properties that should be exhibited by a valid measure of this construct. Responses of 223 male and 338 female undergraduates to the PRF ANDRO and the BSRI were factor analyzed separately for sex-typed and non-sex-typed groups. Results show consistent and theoretically predictable differences in the factor solutions of these 2 groups. The sex-typed or gender-schematic group obtained bipolar factors, with masculine items loading with one sign, whereas feminine items loaded with the other sign on each factor. Also, sex of S loaded highly on almost every factor for this group. The non-sex-typed group, however, obtained few such distinctly dichotomous factors, and sex of S loaded only on the weaker factors. Results support the construct validity of the BSRI and the PRF ANDRO for use in researching the implications of the gender schema approach. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Protein,Fiber, and Mineral Nutrition of Growing Dairy Goats

Seven yearling Alpine does were in a series of balance trials to determine apparent utilization of fiber, protein, and minerals. The 34 kg does consumed 2.2% body weight of a hay-concentrate ration that was 18.8% crude protein, 40.9% neutral detergent fiber, 24.7% acid detergent fiber, 1.18% calcium, .67% phosphorus, .39% magnesium, .98% potassium, and .48% sodium. Digestion coefficients were 59.5, 68.5, 42.3, 70.6, and 29.3 for dry matter, crude protein, neutral detergent fiber, hemicellulose, and acid detergent fiber. Retention (g/day) was: 2.6, 1.3, 2.1, 1.8, and 1.1 for calcium, phosphorus, potassium, sodium, and magnesium. Nitrogen intake was related in a positive linear fashion to fecal nitrogen, urinary nitrogen, and absorbed nitrogen. Apparent absorption rates were 2.7, 1.4, 1.3, 5.1, and 3.2 g per doe per day for calcium, phosphorus, magnesium, potassium, and sodium. Mineral retentions as percent of grams apparently absorbed were 96.2, 88.2, 80.9, 37.7, and 56.0.     

Handoffs in Cellular Wireless Networks: The Daedalus Implementation and Experience

Network protocols in cellular wireless data networks must update routes as a mobile host moves between cells. These routing updates combined with some associated state changes are called handoffs. Most current handoff schemes in wireless networks result in data loss or large variations in packet delivery times. Unfortunately, many applications, such as real-time multimedia applications and reliable transport protocols, adapt to long term estimates of end-to-end delay and loss. Violations and rapid fluctuations of these estimates caused by handoff processing often result in degraded performance. For example, loss during handoff adversely affects TCP performance [4], and high packet loss and variable delays result in poor real-time multimedia performance. In this paper, we describe a multicast-based protocol that eliminates data loss and incurs negligible delays during a handoff. The basic technique of the algorithm is to anticipate a handoff using wireless network information in the form of received signal strengths and to multicast data destined for the mobile host to nearby base stations in advance. This routing, combined with intelligent buffering techniques at the base stations, enables very rapid routing updates and eliminates data loss without the use of explicit data forwarding. We have implemented this protocol using IP Multicast and Mobile IP-like routing. In our implementation, handoffs typically take between 8 and 15 ms to complete and result in no data loss.     

Vertical handoffs in wireless overlay networks

No single wireless network technology simultaneously provides a low latency, high bandwidth, wide area data service to a large number of mobile users. Wireless Overlay Networks - a hierarchical structure of room-size, building-size, and wide area data networks - solve the problem of providing network connectivity to a large number of mobile users in an efficient and scalable way. The specific topology of cells and the wide variety of network technologies that comprise wireless overlay networks present new problems that have not been encountered in previous cellular handoff systems. We have implemented a vertical handoff system that allows users to roam between cells in wireless overlay networks. Our goal is to provide a user with the best possible connectivity for as long as possible with a minimum of disruption during handoff. Results of our initial implementation show that the handoff latency is bounded by the discovery time, the amount of time before the mobile host discovers that it has moved into or out of a new wireless overlay. This discovery time is measured in seconds: large enough to disrupt reliable transport protocols such as TCP and introduce significant disruptions in continuous multimedia transmission. To efficiently support applications that cannot tolerate these disruptions, we present enhancements to the basic scheme that significantly reduce the discovery time without assuming any knowledge about specific channel characteristics. For handoffs between room-size and building-size overlays, these enhancements lead to a best-case handoff latency of approximately 170 ms with a 1.5% overhead in terms of network resources. For handoffs between building-size and wide-area data networks, the best-case handoff latency is approximately 800 ms with a similarly low overhead. This revised version was published online in June 2006 with corrections to the Cover Date.     

Irrelevant information in probabilistic categorization.

Using a probabilistic category learning paradigm, 6 experiments explored irrelevant information and 4 current models. Utilization of relevant configural information was lowered by the presence of an irrelevant dimension, both if that was the only relevant information and if a dimension was also relevant. An irrelevant cue value lowered the utilization of relevant cue values. An additional relevant dimension had a larger degrading effect on the utilization of a relevant dimension than an additional irrelevant dimension, thereby suggesting that the effect of irrelevant information is due to the complexity of the environment rather than to factors particular to the irrelevant nature of the information. The current models failed to fit the findings. However, results showing that memory errors account for salience effects provide a direction for revising one of the models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Factor structure of the Graduate Record Examinations General Test in handicapped and nonhandicapped groups.

We used confirmatory factor analysis to investigate the structure of the Graduate Record Examinations General Test across handicapped and nonhandicapped groups. A simple three-factor model, consisting of verbal, quantitative, and analytical item types, was posed and tested for model fit. In addition, a higher order factor solution was computed to investigate the meaning of General Test total scores and to probe observed discrepancies in factor structure. Results suggested that the three-factor model fit better than simpler models but less well than a four-factor solution. The three-factor model showed particular problems in fit for visually impaired students taking a large-type examination and for physically impaired examinees taking a standard administration. For these groups, the item types composing the Analytical factor did not appear to function effectively as a single factor. For the large-type group, in particular, these item types exhibited different relations with the other factors, had different relations with the test's general factor, and appeared to produce different scale units. Results suggest that Analytical scores and total scores (Verbal?+?Quantitative?+?Analytical) may have different meanings across handicapped and nonhandicapped groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Water Use and Conservation in Manufacturing: Evidence from U.S. Microdata

Water can be a scarce resource, particularly in certain places at certain times. Understanding both water use and conservation efforts can help ensure that limited supplies can meet the demands of a growing population and economy. This paper examines water use and recirculation in the U.S. manufacturing sector, using newly recovered microdata from the Survey of Water Use in Manufacturing, merged with establishment-level data from the Annual Survey of Manufactures and the Census of Manufactures. Results suggest that water use per unit of output is largest for larger establishments, in part because larger establishments use water for more purposes. Larger establishments are also found to recirculate water more — satisfying demand (water use) without necessarily increasing water intake. Various costs also appear to play a role in water recirculation. In particular, the water circulation rate is found to be higher when water is purchased from a utility. Relatively low (internal) prices for self-supplied water could suppress the incentive to invest in recirculation. Meanwhile, establishments with higher per-gallon intake treatment costs also recirculate more, as might be expected. The cost associated with water discharge – due to regulation or otherwise – also increases circulation rates. The aridity of a locale is found to have little effect on circulation rates.     

The assembly and use of a computerized torque rheometer

The personal computer has started a revolution in the way data is collected and stored by bringing computer capabilities within the economic reach of even the smallest company. Computer data acquisition and manipulation expands the usefulness of the already valuable torque rheometer as a tool for both rheological studies and routine quality control testing. Analysis of more fundamental rheological properties than just the traditional torque vs. time curve is possible without the time consuming manual data manipulation. Data storage and recall of routine or Q.C. testing for accurate comparisons of results is made easier. Torque rheometer uses made easier by the use of a computer are reviewed. Also given are details of how to hook up a personal computer to an existing torque rheometer.     

A review of nonlinear oscillatory shear tests: Analysis and application of large amplitude oscillatory shear (LAOS)

Dynamic oscillatory shear tests are common in rheology and have been used to investigate a wide range of soft matter and complex fluids including polymer melts and solutions, block copolymers, biological macromolecules, polyelectrolytes, surfactants, suspensions, emulsions and beyond. More specifically, small amplitude oscillatory shear (SAOS) tests have become the canonical method for probing the linear viscoelastic properties of these complex fluids because of the firm theoretical background [1], [2], [3] and [4] and the ease of implementing suitable test protocols. However, in most processing operations the deformations can be large and rapid: it is therefore the nonlinear material properties that control the system response. A full sample characterization thus requires well-defined nonlinear test protocols. Consequently there has been a recent renewal of interest in exploiting large amplitude oscillatory shear (LAOS) tests to investigate and quantify the nonlinear viscoelastic behavior of complex fluids. In terms of the experimental input, both LAOS and SAOS require the user to select appropriate ranges of strain amplitude (γ₀) and frequency (ω). However, there is a distinct difference in the analysis of experimental output, i.e. the material response. At sufficiently large strain amplitude, the material response will become nonlinear in LAOS tests and the familiar material functions used to quantify the linear behavior in SAOS tests are no longer sufficient. For example, the definitions of the linear viscoelastic moduli G′(ω) and G″(ω) are based inherently on the assumption that the stress response is purely sinusoidal (linear). However, a nonlinear stress response is not a perfect sinusoid and therefore the viscoelastic moduli are not uniquely defined; other methods are needed for quantifying the nonlinear material response under LAOS deformation. In the present review article, we first summarize the typical nonlinear responses observed with complex fluids under LAOS deformations. We then introduce and critically compare several methods that quantify the nonlinear oscillatory stress response. We illustrate the utility and sensitivity of these protocols by investigating the nonlinear response of various complex fluids over a wide range of frequency and amplitude of deformation, and show that LAOS characterization is a rigorous test for rheological models and advanced quality control.