Existing ABR algorithms face a significant challenge in estimating future capacity: capacity can vary widely over time, a phenomenon commonly observed in commercial services. In this work, we suggest an alternative approach: rather than presuming that capacity estimation is required, it is perhaps better to begin by using only the buffer, and then ask when capacity estimation is needed. We test the viability of this approach through a series of experiments spanning millions of real users in a commercial service. We start with a simple design which directly chooses the video rate based on the current buffer occupancy. Our own investigation reveals that capacity estimation is unnecessary in steady state; however using simple capacity estimation (based on immediate past throughput) is important during the startup phase, when the buffer itself is growing from empty. This approach allows us to reduce the rebuffer rate by 10-20% compared to Netflix's then-default ABR algorithm, while delivering a similar average video rate, and a higher video rate in steady state.

The initiation of interaction in face-to-face environments is a gradual process, and takes place in a rich information landscape of awareness, attention, and social signals. One of the main benefits of this process is that people can be more sensitive to issues of privacy and interruption while they are moving towards interaction. However, on-line communication tools do not provide this subtlety, and often lead to unwanted interruptions. We have developed a prototype message system called OpenMessenger (OM) that adds the idea of gradual initiation of interaction to on-line communication. OpenMessenger provides multiple levels of awareness about people, and provides notification to those about whom information is being gathered. OpenMessenger allows people to negotiate interaction in a richer fashion than is possible with any other current messaging system. Preliminary evaluation data suggest the utility of the approach, but also shows that there are a number of issues yet to be resolved in this area.

Ethnographic studies of the home revealed the fundamental roles that physical locations and context play in how household members understand and manage conventional information. Yet we also know that digital information is becoming increasingly important to households. The problem is that this digital information is almost always tied to traditional computer displays, which inhibits its incorporation into household routines. Our solution, location-dependent information appliances, exploit both home location and context (as articulated in ethnographic studies) to enhance the role of ambient displays in the home setting; these displays provide home occupants with both background awareness of an information source and foreground methods to gain further details if desired. The novel aspect is that home occupants assign particular information to locations within a home in a way that makes sense to them. As a device is moved to a particular home location, information is automatically mapped to that device along with hints on how it should be displayed.

In this work we address reliablefile delivery over mobile broadcast networks, concentrating on the Raptor codes as specified for Multimedia Broadcast/Multicast Services (MBMS) within 3GPP. We start by describing Luby-Transform (LT) codes, which are the first practical fountain codes. Then, using a natural and easy to understand linear algebra notation, we describe Raptor codes as a powerful extension of LT codes. We provide some insight into the Raptor code structure and some guidelines for implementation of encoders and decoders. Finally, some selected simulations verify the good performance of file distribution with Raptor codes as specified in 3GPP. References to a complete set of simulation results are also provided. I. INTRODUCTION

Groupware communicates by sending messages across the network, and groupware programmers use a variety of formats for these messages, such as XML, plain text, or serialized objects. Although these formats have many advantages, they are often so verbose that they overload the system's network resources. Groupware programmers could improve efficiency by using more compact formats, but this efficiency comes at the cost of increased complexity, reduced convenience, and reduced readability. In this paper we propose an alternate approach for improving efficiency -- an automatic compression system that transparently minimizes verbose formats. Our general message compressor -- GMC -- automatically finds and removes redundancy in message streams, without any knowledge of the contents or structure of the message, and without any need for the programmer to change the way they work. In tests with realistic message traces, GMC reduced text messages to 20% of their original size, XML messages to 8% of the original, and serialized objects to 9%. Although not as compact as a hand-coded representation, GMC provides most of the compression benefits with almost none of the work -- it allows groupware programmers to use convenient message formats without compromising transport efficiency.

Third Generation Partnership Project (3GPP) and Digital Video Broadcasting (DVB) have just recently specified the use Raptor codes in their mobile broadcast file delivery engine. Until today, investigations of the applicability of these codes to the mentioned systems have been carried out by assuming almost exclusively quite simple loss models such as statistically independent radio packet losses. Furthermore, the combination and tradeoffs between physical layer parameters such as transmit power or physical layer for-ward error correction code rates in system design has been completely ignored. In this work we investigate the end-to-end system performance by analyzing the trade-off between physical layer parameters and application layer code. In particular we are interested in determining the optimal system operating points for optimized broadcast file delivery. Parameters such as power allocation, mobility model, physical layer Turbo code rate, raptor code expansion ratio are investigated and a single performance criteria is defined, namely the required energy to deliver a file to at least some high percentage of users. It is shown that typically considered system configurations with high transmit power and low physical layer code rates - resulting in low radio block loss rates - are in general suboptimal for efficient delivery. A careful tradeoff the system parameters can reduce the required resources in the order of a magnitude.