Telcordia Technologies

About: Telcordia Technologies is a based out in . It is known for research contribution in the topics: Network packet & Node (networking). The organization has 3097 authors who have published 4737 publications receiving 237882 citations.

Distorted chain sites for Co- and Fe-substituted Y Ba 2 Cu 3 O 7 − δ

Abstract: We present x-ray-absorption fine-structure (XAFS) measurements for a series of Co- and Fe-substituted samples of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (Y-Ba-Cu-O). Our analysis of the first- and second-neighbor environments indicates that the Co atoms primarily replace the Cu in the chain sites, the Cu(1) atoms, in Y-Ba-Cu-O, but many of these Co(1) sites and their neighboring oxygen sites are highly distorted. The first-neighbor Co-O peak consists of \ensuremath{\sim}3.5 oxygen at 1.8 \AA{} and \ensuremath{\sim}1.3 oxygen at 2.4 \AA{}, while the second-neighbor multipeak in the XAFS data is unexpectedly low in amplitude. Structure in this peak is inconsistent with a simple Gaussian broadening and indicates that several Co(1)-Ba distances exist. We propose an aggregation of the Co atoms into distorted, zigzag chains along the $〈110〉$ directions, with some of the Co displaced off center by \ensuremath{\sim}0.4 \AA{} along a perpendicular $〈110〉$ direction. This model is consistent with the second-neighbor XAFS data, provides an explanation for the tetragonal structure via twinning on a microscopic scale, and accommodates excess oxygen within the Co chains. The Fe data suggest that similar chains also exist in the Fe-substituted samples. There are, however, some differences between the local environments of the Fe and Co. The primary difference is that a small but significant number of Fe atoms occupy the Cu(2) plane sites while no appreciable number of Co atoms are found on the Cu(2) sites in the more dilute samples. Finally, near-edge measurements on the Co and Fe $K$-absorption edges indicate that the valence is primarily +3, but a mixture of valences exists. For Co, the edge position corresponds to a mixture of +2 and +3 valences, while Fe exists in a mixture of +2, +3, and +4 states.

PACS: Personal Access Communications System-a tutorial

Abstract: The Personal Access Communications System (PACS) is an American National Standards Institute common air interface standard developed for the 1.9 GHz PCS band in the United States. PACS uses frequency division duplexing technology and is optimized to support low-mobility pedestrian outdoor usage and wireless local loop applications in a medium-range environment. PACS-Unlicensed B (PACS-UB) is a version of PACS using time division duplexing. PACS-UB has been optimized for private, indoor wireless PBX applications and cordless telephony. Both modes of operation are supported using the same portable hardware and the same signaling protocol.

Network configuration management via model finding

Abstract: Complex, end-to-end network services are set up via the configuration method: each component has a finite number of configuration parameters each of which is set to a definite value. End-to-end network service requirements can be on connectivity, security, performance and fault-tolerance. However, there is a large conceptual gap between end-to-end requirements and detailed component configurations. To bridge this gap, a number of subsidiary requirements are created that constrain, for example, the protocols to be used, and the logical structures and associated policies to be set up at different protocol layers. By performing different types of reasoning with these requirements, different configuration tasks are accomplished. These include configuration synthesis, configuration error diagnosis, configuration error fixing, reconfiguration as requirements or components are added and deleted, and requirement verification. However, such reasoning is currently ad hoc. Network requirements are not even precisely specified hence automation of reasoning is impossible. This is a major reason for the high cost of network management and total cost of ownership. This paper shows how to formalize and automate such reasoning using a new logical system called Alloy. Alloy is based on the concept of model finding. Given a first-order logic formula and a domain of interpretation, Alloy tries to find whether the formula is satisfiable in that domain, i.e., whether it has a model. Alloy is used to build a Requirement Solver that takes as input a set of network components and requirements upon their configurations and determines component configurations satisfying those requirements. This Solver is used in different ways to accomplish the above reasoning tasks. The Solver is illustrated in depth by carrying out a variety of these tasks in the context of a realistic fault-tolerant virtual private network with remote access. Alloy uses modern satisfiability solvers that solve millions of constraints in millions of variables in seconds. However, poor requirements can easily nullify such speeds. The paper outlines approaches for writing efficient requirements. Finally, it outlines directions for future research.

Competitive queue policies for differentiated services

Abstract: We consider the setting of a network providing differentiated services. As is often the case in differentiated services, we assume the packets are tagged as either being high- or low-priority packets. Outgoing links in the network are serviced by a single FIFO queue. Our model gives a benefit of /spl alpha//spl ges/1 to each high-priority packet and a benefit of 1 to each low-priority packet. A queue policy controls which of the arriving packets are dropped and which enter the queue. Once a packet enters the queue it is eventually sent. The aim of a queue policy is to maximize the sum of the benefits of all the packets it delivers. We analyze and compare different queue policies for this problem using the competitive analysis approach, where the benefit of the online policy is compared to the benefit of an optimal offline policy. We derive both upper and lower bounds for the policies we consider, and in most cases our bounds are tight. We believe that competitive analysis gives important insight into the performance of these simple queuing policies.

On computing majority by comparisons

Abstract: The elements of a finite setX (of odd cardinalityn) are divided into two (as yet unknown) classes and a member of the larger class is to be identified. The basic operation is to test whether two objects are in the same class. We show thatn-B(n) comparisons are necessary and sufficient in worst case, whereB(n) is the number of 1's in the binary expansion ofn.