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Networking, IEEE/ACM Transactions on

Issue 3 • Date Jun 1995

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Displaying Results 1 - 12 of 12
  • Improved algorithms for synchronizing computer network clocks

    Page(s): 245 - 254
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    The Network Time Protocol (NTP) is widely deployed in the Internet to synchronize computer clocks to each other and to international standards via telephone modem, radio and satellite. The protocols and algorithms have evolved over more than a decade to produce the present NTP Version 3 specification and implementations. Most of the estimated deployment of 100000 NTP servers and clients enjoy synchronization to within a few tens of milliseconds in the Internet of today. This paper describes specific improvements developed for NTP Version 3 which have resulted in increased accuracy, stability and reliability in both local-area and wide-area networks. These include engineered refinements of several algorithms used to measure time differences between a local clock and a number of peer clocks in the network, as well as to select the best subset from among an ensemble of peer clocks and combine their differences to produce a local dock accuracy better than any in the ensemble. This paper also describes engineered refinements of the algorithms used to adjust the time and frequency of the local clock, which functions as a disciplined oscillator. The refinements provide automatic adjustment of algorithm parameters in response to prevailing network conditions, in order to minimize network traffic between clients and busy servers while maintaining the best accuracy. Finally, this paper describes certain enhancements to the Unix operating system kernel software in order to realize submillisecond accuracies with fast workstations and networks View full abstract»

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  • Delay analysis of a cellular mobile priority queueing system

    Page(s): 310 - 319
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (876 KB)  

    A nonpreemptive priority queueing system incorporating a channel reservation policy and a hysteresis mechanism is considered for use in cellular mobile networks. The aim is to provide for priority for handover attempts over new call. Attempts in such a way as to avoid the forced termination of calls in progress without unduly affecting the performance seen by new call attempts. The system model is found to have a matrix-geometric solution with a phase-type distribution for the handover delay and a matrix-exponential distribution for the delay seen by new call attempts. It is also shown that the system can be represented by an M/G/1 queue with multiple vacations. A new result is derived for the M/G/1 queue with multiple vacations and impatient customers and this allows for the analysis to be extended so that new call arrivals are subject to a fixed timeout in queue. Results are provided which show how nonpreemptive priority in conjunction with channel reservation and hysteresis an provide for fast and efficient handover performance for cellular mobile networks View full abstract»

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  • Minimum-latency transport protocols with modulo-N incarnation numbers

    Page(s): 255 - 268
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1356 KB)  

    To provide reliable connection management, a transport protocol uses 3-way handshakes in which user incarnations are identified by bounded incarnation numbers from some modulo-N space, Cacheing schemes have been proposed to reduce the 3-way handshake to a 2-way handshake, providing the minimum latency desired for transaction-oriented applications. The authors define a class of cacheing protocols and determine the minimum N and optimal cache residency time as a function of real-time constraints (e.g., message lifetime, incarnation creation rate, inactivity duration, etc.). The protocols use the client-server architecture and handle failures and recoveries, Both clients and servers generate incarnation numbers from a local counter (e.g., clock). These protocols assume a maximum duration for each incarnation; without this assumption, there is a very small probability (≈1/N2) of misinterpretation of incarnation numbers. This restriction can be overcome with some additional cacheing View full abstract»

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  • A performance model for ATM switches with general packet length distributions

    Page(s): 299 - 309
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    The maximum throughput of an ATM switch is investigated in the presence of an offered load of multicell packets. For the case of input queueing coupled with a round-robin policy for transferring cells from inputs to outputs, the system is approximated by a product form queueing network. Under the assumption that packet lengths are described by random variables with discrete Coxian distributions, it is shown that the balance equations describing the behavior of the ATM switch approach those for a product form queueing network and that the steady-state probabilities of such an ATM switch approach the product-form solution as the cell length tends to zero. Last, a numerical investigation shows that the approximation yields good results, even when the packet lengths are not well described by Coxian distributions View full abstract»

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  • A new label-based source routing for multi-ring networks

    Page(s): 320 - 328
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    This paper presents a new source routing technique for ring and multi-ring networks, which uses short address labels. The main objectives for having this new method are that in case of one or more failures a frame will be guaranteed: (1) to be removed from the ring-termination property, and (2) to be copied at most once and only by its destinations-safety property. The scheme is based on dividing the label address space of each ring into subspaces, such that the address subspaces are physically disjoint. More specifically, each ring, in a multi-ring network, is divided into two or more parts such that adjacent address subspaces are disjoint. The route of each frame is described by a sequence of short address labels in the frame's header. The current route of a frame is determined by the first address label in its header, and it can be used for routing over at most one subspace of the ring View full abstract»

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  • Wavelength requirements of all-optical networks

    Page(s): 269 - 280
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    All-optical networks are networks for which all data paths remain optical from input to output. With rapid development of optical technology, such networks are a viable choice for the high speed wide area networks of the future. Wavelength division multiple access (WDMA) currently provides the most mature technology for all-optical networks. The authors discuss a class of WDMA networks that are homogeneous in the sense that each node contains both an input/output port and a switch. They focus on the permutation routing problem and first, present a lower bound on the number of wavelengths required for permutation routing as a function of the size and degree of the network. They use particular topologies, including the multistage perfect shuffle, the Debruijn, and the hypercube, to find achievable upper bounds on the number of required wavelengths View full abstract»

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  • Selection of timed token protocol parameters to guarantee message deadlines

    Page(s): 340 - 351
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    Networks that use the timed token protocol (such as the 100 Mbit/s FDDI network) are well suited for real-time applications because they guarantee, to each node, an average bandwidth and a bounded access time to the communication network. This guarantee is necessary but not sufficient for the timely delivery of deadline-constrained messages; protocol parameters must be carefully selected to ensure that these messages meet their deadlines. This paper addresses the issue of selecting the protocol parameters TTRT (target token rotation time) and the synchronous capacities assigned to each node. The objective is to guarantee that each synchronous message is transmitted before its deadline. An upper bound is derived on the worst case achievable utilization (WCAU) of any parameter selection scheme. The WCAU of a scheme is defined as the maximum utilization U such that the scheme guarantees all synchronous messages as long as their utilization is less than U. An algorithm for selecting the above parameters is proposed, The algorithm is shown to have a WCAU that is very close to the upper bound View full abstract»

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  • A heuristic wavelength assignment algorithm for multihop WDM networks with wavelength routing and wavelength re-use

    Page(s): 281 - 288
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    Presents a heuristic algorithm for effectively assigning a limited number of wavelengths among the access stations of a multihop network wherein the physical medium consists of optical fiber segments which interconnect wavelength-selective optical switches. Such a physical medium permits the limited number of wavelengths to be re-used among the various fiber links, thereby offering very high aggregate capacity. Although the optical connectivity among the access station can be altered by changing the states of the various optical switches, the resulting optical connectivity pattern is constrained by the limitation imposed at the physical level. The authors also study two routing schemes, used to route requests for virtual connections. The heuristic is tested on a realistic traffic model, and the call blocking performance of new requests for virtual connections is studied through extensive simulations and compared against the blocking performance of an ideal infinite capacity centralized switch (lowest possible call blocking caused exclusively by congestion on the finite capacity user input/output links, never by the switch fabric itself). Surprisingly, the authors find that, for a wide range of parameters, the blocking performance of the lightwave network is almost the same as that of the ideal centralized switch. From these results, they conclude that the heuristic algorithm is effective and the routing scheme is efficient View full abstract»

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  • Wide area traffic: the failure of Poisson modeling

    Page(s): 226 - 244
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    Network arrivals are often modeled as Poisson processes for analytic simplicity, even though a number of traffic studies have shown that packet interarrivals are not exponentially distributed. We evaluate 24 wide area traces, investigating a number of wide area TCP arrival processes (session and connection arrivals, FTP data connection arrivals within FTP sessions, and TELNET packet arrivals) to determine the error introduced by modeling them using Poisson processes. We find that user-initiated TCP session arrivals, such as remote-login and file-transfer, are well-modeled as Poisson processes with fixed hourly rates, but that other connection arrivals deviate considerably from Poisson; that modeling TELNET packet interarrivals as exponential grievously underestimates the burstiness of TELNET traffic, but using the empirical Tcplib interarrivals preserves burstiness over many time scales; and that FTP data connection arrivals within FTP sessions come bunched into “connection bursts”, the largest of which are so large that they completely dominate FTP data traffic. Finally, we offer some results regarding how our findings relate to the possible self-similarity of wide area traffic View full abstract»

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  • Bandwidth quantization and states reduction in the broadband ISDN

    Page(s): 352 - 360
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    If a network supports only certain rates, we say its bandwidth is quantized. In a quantized-bandwidth network, a customer may be forced to use the next higher rate if the requested rate is not supported. The result is a higher blocking probability and a lower throughput. The throughput loss due to quantization is called the quantization loss, and its related issues are the focus of this paper. We show that the quantization loss is insensitive to capacity scaling and traffic-loading. More important, it is hardly as large as is thought. Even for a network, such as ATM, intending to support a continuous bit rate, bandwidth quantization can be a powerful tool for states reduction. States reduction is shown to be indispensable for solving many problems, such as routing and capacity planning, of a broadband network View full abstract»

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  • Traffic descriptors for VBR video teleconferencing over ATM networks

    Page(s): 329 - 339
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    This paper examines the problem of video transport over ATM networks using knowledge of both video system design and broadband networks. The following issues are addressed: video system delay caused by internal buffering, traffic descriptors (TD) for video, and call admission. We find that while different video sequences require different TD parameters, the following trends hold for all sequences examined. First, increasing the delay in the video system decreases the necessary peak rate and significantly increases the number of calls that can be carried by the network. Second, as an operational traffic descriptor for video, the leaky-bucket algorithm appears to be superior to the sliding-window algorithm. And finally, with a delay in the video system, the statistical multiplexing gain from VBR over CBR video is upper bounded by roughly a factor of four, and to obtain a gain of about 2.0 can require the operational traffic descriptor to have a window or bucket size on the order of a thousand cells. We briefly discuss how increasing the complexity of the video system may enable the size of the bucket or window to be reduced View full abstract»

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  • A new structural property of statistical data forks

    Page(s): 289 - 298
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    The paper presents a method of controlling the pattern of packet flow in the statistical data fork (SDF), such that the output channels are assigned to a channel group based only on their addresses and this assignment is maintained independently of the offered load to the SDF. The proposed method is realized by using a structural property of the SDF which is derived in the paper. It is shown that a sufficient condition for this property to hold is for the probabilities of packets destined for different channel groups to be certain permutations of each other. It is shown, using this property, that the flow of packets in the SDF can be governed by a two phase process wherein in the first phase, packets are routed in different subnetworks to result in the probability patterns that match the requirement of the structural property, and in the second phase, these packets are delivered to the channel groups which are partitioned only according to their addresses View full abstract»

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Aims & Scope

The IEEE/ACM Transactions on Networking’s high-level objective is to publish high-quality, original research results derived from theoretical or experimental exploration of the area of communication/computer networking.

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Meet Our Editors

Editor-in-Chief
R. Srikant
Dept. of Electrical & Computer Engineering
Univ. of Illinois at Urbana-Champaign