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Access type: Open accessAuthor: search.filters.author.Chan, CT

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    High-energy zero-norm states and symmetries of string theory
    (2006-05-05)
    Chan, CT
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    Ho, PM
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    Lee, JC
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    Teraguchi, S
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    Yang, Y
    High-energy limit of zero-norm states in the old covariant first quantized spectrum of the 26D open bosonic string, together with the assumption of a smooth behavior of string theory in this limit, are used to derive infinitely many linear relations among the leading high-energy, fixed-angle behavior of four-point functions of different string states. As a result, ratios among all high-energy scattering amplitudes of four arbitrary string states can be calculated algebraically and the leading order amplitudes can be expressed in terms of that of four tachyons as conjectured by Gross in 1988. A dual calculation can also be performed and equivalent results are obtained by taking the high-energy limit of Virasoro constraints. Finally, we compute all high-energy scattering amplitudes of three tachyons and one massive state at the leading order by saddle-point approximation to verify our results.
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    Anatomy of zero-norm states in string theory
    (2005-04-01)
    Chan, CT
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    Lee, JC
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    Yi-Yang
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    電子物理學系
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    Department of Electrophysics
    We calculate and identify the counterparts of zero-norm states in the old covariant first quantized (OCFQ) spectrum of open bosonic string in two other quantization schemes of string theory, namely, the light-cone Del Giudice-Di Vecchia-Fubine zero-norm states and the off-shell Becchi-Rouet-Stora-Tyutin (BRST) zero-norm states (with ghost) in the Witten string field theory (WSFT). In particular, special attention is paid to the interparticle zero-norm states in all quantization schemes. For the case of the off-shell BRST zero-norm states, we impose the no-ghost conditions and recover exactly two types of on-shell zero-norm states in the OCFQ string spectrum for the first few low-lying mass levels. We then show that off-shell gauge transformations of WSFT are identical to the on-shell stringy gauge symmetries generated by two types of zero-norm states in the generalized massive sigma-model approach of string theory. The high-energy limit of these stringy gauge symmetries was recently used to calculate the proportionality constants, conjectured by Gross, among high-energy scattering amplitudes of different string states. Based on these zero-norm state calculations, we have thus related gauge symmetry of WSFT to the high-energy stringy symmetry of Gross.
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    Design and analysis of delay control for CBR services in ATM networks
    (1998-05-15)
    Chen, YC
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    Chan, CT
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    Hu, SC
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    資訊工程學系
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    Department of Computer Science
    Asynchronous transfer mode (ATM) networks are designed to provide end-to-end transport of user data via virtual connections with specified quality of services (QOS), which is expected to be satisfied through effective traffic control mechanisms. This paper presents an adaptive delay-jitter control (ADJC) method that guarantees the delay bounds of constant bit rate (CBR) services in ATM networks. Our proposed method is based on a node-by-node time-frame scheme. Through both mathematical derivation and simulation, we have demonstrated that ADJC features a significant improvement over existing approaches in jitter delay, which can be reduced to one time-frame from end-to-end for CBR traffic. Simulation results have shown that CBR services receive satisfactory delay performance using our approach. (C) 1998 Elsevier Science B.V.
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    Frame-based priority scheduling in hybrid IP/ATM networks
    (1999-08-25)
    Chen, YC
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    Hu, SC
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    Chan, CT
    ;
    Lee, CL
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    資訊工程學系
    The exploding growth of World Wide Web applications in recent years has overwhelmed the internet with multimedia traffic. A future performance concern is to keep pace with the quickly growing bandwidth requirements. IP over ATM is a way to relax such requirements. It provides a hybrid approach to support both layer 3 software forwarding and layer 2 ATM hardware switching. A switched virtual connection may be suitable for traffic involving large data transfers and QoS provision like Guarantee Service (GS) applications. In the hybrid IP/ATM networks, the packet-level instead of the cell-Level behavior is the relevant measure of performance. In this paper, we propose a so-called Frame-based Priority Scheduling (FBPS) algorithm far GS applications. FBPS focuses on the packet-level performance while transmitting based on cells. The most attractive feature of FBPS is its simplicity. We provide a systematic analysis of FBPS scheduler and derive the bound on its fairness when the how traffic is shaped by a leaky bucket. It shows that FBPS is competitive with certain complex scheduling disciplines such as PGPS. We also verify our analytical bounds by simulation. (C) 1999 Elsevier Science B.V. All rights reserved.
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    Design and analysis of traffic control for guaranteed services on the Internet
    (2000-05-01)
    Wang, PC
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    Chan, CT
    ;
    Chen, YC
    ;
    資訊工程學系
    ;
    Department of Computer Science
    Real-time communications services will be one of the most promising applications on the Internet. Real-time traffic usually utilizes a significant amount of resources while traversing through the network. To provide guaranteed service for delay-sensitive real-time applications, both resource reservation and effective traffic control are necessary. The resource reservation protocol (RSVP) was developed to deal with the former problem while various approaches have been proposed to solve the latter one. It is crucial for guaranteed services to maintain satisfactory performance through effective traffic control, which must be implemented in a feasible way and be able to work with RSVP. In this article, we present a flexible and effective traffic-control approach with a resource reservation scheme to accommodate delay-sensitive services on the Internet. We demonstrate that our approach features proven bounded end-to-end queueing delay for delay-sensitive applications and good resilience for resource allocation. In addition, our packet transmission discipline achieves significant improvement in end-to-end delay control.
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    A FIFO-based buffer management approach for the ATM GFR services
    (2000-06-01)
    Chan, CT
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    Hu, SC
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    Wang, PC
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    Chen, YC
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    資訊工程學系
    We investigate the TCP packet transmission over the ATM Guaranteed Frame Rate (GFR) service using a selective packet-discard with buffer vacancy tracking strategy and a packet-based push-out buffering scheme. Our approach is based on FIFO queueing discipline, it features fair sharing of available resources as well as feasibility in hardware implementation.
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    An intelligent buffer management approach for GFR services in IP/ATM internetworks
    (2000-08-30)
    Wang, PC
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    Chan, CT
    ;
    Chen, YC
    ;
    資訊工程學系
    ;
    Department of Computer Science
    In ATM networks, the Guaranteed Frame Rate (GFR) service has been proposed to accommodate non-real-time traffic with packet size not exceeding a maximum length, such as TCP/IP based traffic. The GFR service not only guarantees a minimum throughput at the frame level, but also supports a fair share of available resources. In this article, we propose a buffering strategy called Intelligent Fair Buffer Allocation (IFBA) that provides minimum cell rate (MCR) guarantees and fair sharing to GFR virtual circuits (VCs). From the simulation results, we demonstrate that IFBA fulfills the requirements of GFR service as well as improves the TCP throughput using the FIFO scheduling. (C) 2000 Elsevier Science B.V. All rights reserved.
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    A fast IP routing lookup scheme
    (2001-03-01)
    Wang, PC
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    Chan, CT
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    Chen, YC
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    資訊工程學系
    ;
    Department of Computer Science
    A major issue in router design for the next generation Internet is the fast IP address lookup mechanism. The existing scheme by Huang et al. performs the IP address lookup in hardware in which the forwarding table can be compressed to fit into reasonable-size SRAM, and a lookup can be accomplished in three memory accesses. In this letter, we claim that with a little extra memory, it is able to further reduce the lookup time to two memory accesses.
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    Performance enhancement of IP forwarding by reducing routing table construction time
    (2001-05-01)
    Wang, PC
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    Chan, CT
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    Chen, YC
    ;
    資訊工程學系
    ;
    Department of Computer Science
    In previous work, Lampson et al, proposed an IP lookup algorithm which performs binary search on prefixes (BSP) [3], The algorithm is attractive for IPv6 because of its bounded worst-case memory requirement. Although for the sake of fast forwarding, the cost paid for the slowing down insertion is reasonable, the performance of routing-table reconstruction in BGP is too time-consuming to handle the frequent route updates. In this letter, we propose a fast forwarding-table construction algorithm which can handle more than 3600 route updates per second, Moreover, it is simple enough to fulfill the need of fast packet forwarding.
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    An efficient IP routing lookup by using routing interval
    (2001-12-01)
    Wang, PC
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    Chan, CT
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    Chen, YC
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    資訊工程學系
    ;
    Department of Computer Science
    Nowadays, the commonly used table lookup scheme for IP routing is based on the so-called classless interdomain routing (CIDR). With CIDR, routers must find out the best matching prefix (BMP) for IP packets forwarding, this complicates the IP lookup. Currently, this process is mainly performed in software and several schemes have been proposed for hardware implementation. Since the IP lookup performance is a major design issue for the new generation routers, in this article we investigate the properties of the routing table and present a new approach for IP lookups, our approach is not based on BMP and significantly reduces the complexity, thus the computation cost of existing schemes can be significantly reduced. We also propose an efficient IP lookup algorithm, with which we improve the binary search on prefixes to 30 millions of packets per second (MPPS) and 5,000 route updates/s under the same experiment setup with an even larger routing table.