AT&T Labs

About: AT&T Labs is a based out in . It is known for research contribution in the topics: Network packet & The Internet. The organization has 1879 authors who have published 5595 publications receiving 483151 citations.

Dynamic C++ classes: a lightweight mechanism to update code in a running program

Abstract: Techniques for dynamically adding new code to a running program already exist in various operating systems, programming languages and runtime environments Most of these systems have not found their way into common use, however, since they require programmer retraining and invalidate previous software investments In addition, many of the systems are too high-level for performance-critical applications This paper presents an implementation of dynamic classes for the C++ language Dynamic classes allow run-time updates of an executing C++ program at the class level Our implementation is a lightweight proxy class that exploits only common C++ features and can be compiled with most modern compilers The proxy supports version updates of existing classes as well as the introduction of new classes Our language choice and proxy implementation is targeted towards performance-critical applications such as low-level networking in which the use of C++ is already widespread

Quality monitoring of video over a packet network

Abstract: We consider monitoring the quality of compressed video transmitted over a packet network from the perspective of a network service provider. Our focus is on no-reference methods, which do not access the original signal, and on evaluating the impact of packet losses on quality. We present three methods to estimate mean squared error (MSE) due to packet losses directly from the video bitstream. NoParse uses only network-level measurements (like packet loss rate), QuickParse extracts the spatio-temporal extent of the impact of the loss, and FullParse extracts sequence-specific information including spatio-temporal activity and the effects of error propagation. Our simulation results with MPEG-2 video subjected to transport packet losses illustrate the performance possible using the three methods.

Error-resilient transcoding for video over wireless channels

Abstract: We describe a method to maintain quality for video transported over wireless channels. The method is built on three fundamental blocks. First, we use a transcoder that injects spatial and temporal resilience into an encoded bitstream. The amount of resilience is tailored to the content of the video and the prevailing error conditions, as characterized by bit error rate. Second, we derive analytical models that characterize how corruption propagates in a video that is compressed using motion-compensated encoding and subjected to bit errors. Third, we use rate distortion theory to compute the optimal allocation of bit rate among spatial resilience, temporal resilience, and source rate. Furthermore, we use the analytical models to generate the resilience rate distortion functions that are used to compute the optimal resilience. The transcoder then injects this optimal resilience into the bitstream. Simulation results show that using a transcoder to optimally adjust the resilience improves video quality in the presence of errors while maintaining the same input bit rate.

Animation of synthetic faces in MPEG-4

Abstract: MPEG-4 is the first international standard that standardizes true multimedia communication-including natural and synthetic audio, natural and synthetic video, as well as 3D graphics. Integrated into this standard is the capability to define and animate virtual humans consisting of synthetic heads and bodies. For the head, more than 70 model-independent animation parameters defining low-level actions like "move left mouth corner" up to high-level parameters like facial expressions and visemes are standardized In a communication application. The encoder can define the face model using MPEG-4 BIFS (BInary Format for Scenes) and transmit it to the decoder. Alternatively, the encoder can rely on a face model that is available at the decoder. The animation parameters are quantized, predictively encoded using an arithmetic encoder or a DCT. The decoder receives the model and the animation parameters in order to animate the model. Since MPEG-4 defines the minimum MPEG-4 terminal capabilities in profiles and levels, the encoder knows the quality of the animation at the decoder.

Internet Packet Filter Management and Rectangle Geometry

Abstract: We consider rule sets for internet packet routing and filtering, where each rule consists of a range of source addresses, a range of destination addresses, a priority, and an action. A given packet should be handled by the action from the maximum priority rule that matches its source and destination. We describe new data structures for quickly finding the rule matching an incoming packet, in near-linear space, and a new algorithm for determining whether a rule set contains any conflicts, in time O(n^{3/2}).