K. Maxwell

Bio: K. Maxwell is an academic researcher. The author has contributed to research in topics: Telephone line & Local area network. The author has an hindex of 1, co-authored 1 publications receiving 118 citations.

Asymmetric digital subscriber line: interim technology for the next forty years

Abstract: The Internet has surfaced as the dominant early market for residential broadband. ADSL, a transmission system capable of realizing rates from 1 to Mb/s over existing telephone lines, fits Internet access requirements perfectly, and offers telephone companies a tool for connecting virtually all Internet users at megabit rates before the next century. ADSL is asymmetric-high-speed downstream, lower-speed upstream-to counteract speed limitations imposed by line length and crosstalk. The transmission technology itself has two essential forms, single-carrier and multicarrier, which must press Shannon's limit to squeeze so many bits through so little bandwidth. With complicated line coding and other features such as integral forward error correction and ATM/Ethernet mode interfaces, ADSL will be the most complex modem ever attached to a telephone line. This will not prevent ADSL from reaching consumer-level pricing within the next two years. We can expect some commercial deployment in 1997 and virtually ubiquitous availability by the end of 1999.

Spatial traffic estimation and characterization for mobile communication network design

Abstract: This paper presents a new method for the estimation and characterization of the expected teletraffic in mobile communication networks. The method considers the teletraffic from the network viewpoint. The traffic estimation is based on the geographic traffic model, which obeys the geographical and demographical factors for the demand for mobile communication services. For the spatial teletraffic characterization, a novel representation technique is introduced which uses the notion of discrete demand nodes. We show how the information in geographical information systems can be used to estimate the teletraffic demand in an early phase of the network design process. Additionally, we outline how the discrete demand node representation facilitates the application of demand-based automatic mobile network design algorithms.

A telecommunications system for providing both narrowband and broadband services to subscribers

Abstract: An architecture, as well as various components, of an asynchronous transfer mode (ATM) subscriber access multiplexer (ASAM) system can be implemented using an XDSL (x-Digital Subscriber Line) using DMT (Discrete Multitone) or CAP (Carrierless Amplitude Phase Modulation) between a plurality of subscribers and a corresponding plurality of line termination equipment in a shelf that also includes network termination equipment for connection to an ATM network. The line termination and network termination equipment are interconnected by a bus internal to the shelf for providing subscriber access. Separate lowpass filters are provided at each end of a twisted wire pair between the shelf and each subscriber equipment. A shelf can be used as a hub for connecting to a remote shelf that includes the line termination equipment for connection to subscribers. Although the internal bus of the shelf is shown in a non-redundant embodiment, an increased level of equipment protection can be provided by placing one half of a redundant equipment pair in one shelf and the other half in the other shelf and sharing network termination equipment between such shelves.

Ethernet transport facility over digital subscriber lines

Abstract: A facility transport system for transporting Ethernet over digital subscriber lines. The system, termed 10BaseS, is capable of transmitting of 10 Mbps Ethernet over existing copper infrastructure. The system utilizes carrierless amplitude modulation phase modulation/quadrature amplitude modulation (CAP/QAM) to transport Ethernet frame data and utilizes splitter means (22) to separate both the downstream and upstream channels from POST signals.

A low power 128-tap digital adaptive equalizer for broadband modems

Abstract: This chip provides programmable fractional spacings and slicers making it suitable for 51Mb/s and 155Mb/s ATM over CAT3, as well as for the emerging 100Mb/s base-T2 fast Ethernet standard. The primary design goal is to minimize the power consumption so that the equalizer may be integrated into low-cost single-chip transceivers. Two 64-tap adaptive FIR filters are configured in parallel as in-phase and quadrature filters. Each has a span of l6T, where T is the symbol period, and is programmable to operate with T/2, T/3 or T/4 fractional spacing. On-chip programmable slicers enable slicing of up to 8x8 constellations. They use a reduced constellation for blind training and switch to the full constellation to obtain final convergence. The filters feature a zero latency cascadable systolic FIR structure that has the low power advantages of the direct form due to the reduced number of flip-flops in the output path, as well as the reduced critical path advantages of the transposed form. A programmable delay synchronizes the input data with the coefficients and the error for correct least mean squares (LMS) coefficient adaption with different fractional spacings.

Improving TCP throughput over two-way asymmetric links: analysis and solutions

Abstract: The sharing of a common buffer by TCP data segments and acknowledgments in a network or internet has been known to produce the effect of ack compression, often causing dramatic reductions in throughput. We study several schemes for improving the performance of two-way TCP traffic over asymmetric links where the bandwidths in the two directions may differ substantially, possibly by many orders of magnitude. These approaches reduce the effect of ack compression by carefully controlling the flow of data packets and acknowledgments. We first examine a scheme where acknowledgments are transmitted at a higher priority than data. By analysis and simulation, we show that prioritizing acks can lead to starvation of the low-bandwidth connection. Next, we introduce and analyze a connection-level backpressure mechanism designed to limit the maximum amount of data buffered in the outgoing IP queue of the source of the low-bandwidth connection. We show that this approach, while minimizing the queueing delay for acks, results in unfair bandwidth allocation on the slow link. Finally, our preferred solution separates the acks from data packets in the outgoing queue, and makes use of a connection-level bandwidth allocation mechanism to control their bandwidth shares. We show that this scheme overcomes the limitations of the previous approaches, provides isolation, and enables precise control of the connection throughputs. We present analytical models of the dynamic behavior of each of these approaches, derive closed-form expressions for the expected connection efficiencies in each case, and validate them with simulation results.