Showing papers on "Transmission delay published in 1978"

Reverse path forwarding of broadcast packets

Abstract: A broadcast packet is for delivery to all nodes of a network. Algorithms for accomplishing this delivery through a store-and-forward packet switching computer network include (1) transmission of separately addressed packets, (2) multidestination addressing, (3) hot potato forwarding, (4) spanning tree forwarding, and (5) source based forwarding. To this list of algorithms we add (6) reverse path forwarding, a broadcast routing method which exploits routing procedures and data structures already available for packet switching. Reverse path forwarding is a practical algorithm for broadcast routing in store-and-forward packet switching computer networks. The algorithm is described as being practical because it is not optimal according to metrics developed for its analysis in this paper, and also because it can be implemented in existing networks with less complexity than that required for the known alternatives.

A Basic Dynamic Routing Problem and Diffusion

Abstract: Diffusion theory has sometimes been successful in providing excellent approximate solutions to difficult queueing problems. Here we explore whether such methods can be used to analyze a basic dynamic routing strategy associated with a single idealized node in a data network. We analyze a dynamic routing policy where messages, or packets, that arrive at a certain node are routed to leave the node on the link having the shorter queue. In the model, message or packet arrivals are Poisson and the service time is exponentially distributed. We explore a heavy traffic diffusion method and we also discuss the limitations of an ad hoc approach to applying diffusion. For a node with K outgoing queues we find, under the assumption of heavy traffic, the optimum dynamic strategy, in the sense of minimizing the average delay. When this optimum dynamic strategy is compared to a static strategy where the outgoing traffic is split among the K queues, we find that the average delay for the dynamic system is better by a factor of K .

The evolution of packet switching

Abstract: Over the past decade data communications has been revolutionized by a radically new technology called packet switching. In 1968 virtually all interactive data communication networks were circuit switched, the same as the telephone network. Circuit switching networks preallocate transmission bandwidth for an entire call or session. However, since interactive data traffic occurs in short bursts 90 percent or more of this bandwidth is wasted. Thus, as digital electronics became inexpensive enough, it became dramatically more cost-effective to completely redesign communications networks, introducing the concept of packet switching where the transmission bandwidth is dynamically allocated, permitting many users to share the same transmission line previously required for one user. Packet switching has been so successful, not only in improving the economics of data communications but in enhancing reliability and functional flexibility as well, that in 1978 virtually all new data networks being built throughout the world are based on packet switching. An open question at this time is how long will it take for voice communications to be revolutionized as well by packet switching technology. In order to better understand both the past and future evolution of this fast moving technology, this paper examines in detail the history and trends of packet switching.

A Microprocessor-Based PSK Modem for Packet Transmission Over Satellite Channels

Abstract: This paper describes a microprocessor-based modem developed for use in a packet switching network over satellite channels. This digital modem can process both BPSK and QPSK packets with near optimum error rate performance over channels with marginal signal energy-to-noise density ratio. Of principal concern is the development of the discrete time algorithms which form the basis of the microinstruction program. The processing of a packet can be decomposed into two basic stages: (1) the detection of the packet preamble and the rapid estimation of signal parameters (symbol timing and carrier frequency offset) for the specific packet, and (2) the demodulation of the data portion of the packet including the tracking of both symbol timing and carrier offset phase, phase ambiguity resolution and data symbol estimation. The paper concludes with details on the performance of the modem under operational conditions and a brief discussion of implementation of the processor.

Queueing Network Modeling of Computer Communication Networks

Abstract: The application of queueing network models to the performance analysis of messageswitched (or packet-switched) commumcatmn networks m surveyed. The main topics covered are the analysis of end-to-end delay and the analysis of buffer management schemes. A brief discussmn on flow control is also included. A queueing network model is developed for a simple user-resource network. The mean response time of a host computer m this network is illustrated by a numerical example.

Electronic ultrasonic sector scanning apparatus and method

Abstract: An electronically scanned phased array diagnostic system for describing internal structure of a subject by the use of ultrasonic energy. The system includes a transducer unit with an array of ultrasonic energy conversion segments and control circuitry for actuating the segments to direct ultrasonic energy into the subject. Imaging circuitry is included for interpreting electrical return signals produced by the segments in response to ultrasonic echoes. The imaging circuitry includes transmission delay circuits for imposing time delays on the return signals for steering and focusing system echo reception. Each transmission delay circuit includes first and second delay elements for impressing first and second delay time components on the return signals. Each pair of the first delay elements are coupled in parallel with separate transducer elements, and serially combined with a downstream second delay element The first delay elements provide a portion of the reception steering capability. The second elements provide the remainder of the steering, and the beam focusing, delay. components. The system further includes display apparatus responsive to the delayed return signals for producing an image of the subject's internal structure.

Delay and Throughput Evaluation of Switching Methods in Computer Communication Networks

Abstract: Message, packet and line switching in computer communication networks are analyzed by a queueing model. Message transmission delay time and network throughput between a source-destination node pair are obtained as a function of various parameters including message length, traffic arriving at the network, and the number of switching nodes existing between the nodes. A criterion to determine the most suitable switching method under the given conditions is offered. Also, the maximum length of a packet in packet switching is discussed.

Multiaccess Model for Packet Switching with a Satellite Having Processing Capability: Delay Analysis

Abstract: The multiaccess model for satellite packet switching proposed by the authors [1] employs a frame format, with scheduling assignments broadcast from the satellite. The total delay recurred by a data packet in traversing the satellite channel consists of queueing delay, scheduling delay, transmission delay and propagation delay. In this paper we analyze the queueing and scheduling delays and compare the analytical and simulation results. For the queuemg delay analysis we model the multiaccess scheme using an M/D/N queue, where N is the number of slots per frame. For the scheduling delay analysis we emply a round-robin scheduling assignment algorithm. We treat the cases with and without random transmission; our results indicate that random transmission improves the queueing delay performance.

Delay Decomposition at a Single Server queue with Constant Service Time and Multiple Inputs

Abstract: Two networks consisting of single server queues, each with a constant service time, are considered. The external inputs to each network are assumed to follow some general probability distribution. Several interesting equivaleneies that exist between the two networks considered are derived. This leads to the introduction of an important concept in delay decomposition. It is shown that the waiting time experienced by a customer can be decomposed into two basic components called self delay and interference delay.

Signal compensating system

Abstract: PURPOSE: To substitute a signal, which is obtained by synthesizing signals of upper, lower, right and left cells adjacent to a faulty cell, for the output signal of the faulty cell by regarding the cell as the faulty cell when the output of the specific cell is not between a white level and a black level in the signal compensating system of a solid image sensor. CONSTITUTION: Picture signals from a solid image sensor are applied to delay circuit 1, which has a delay time equal to the scanning time across adjacent cells in the horizontal direction, and delay circuits 2, 2a and 2b which have a delay time equal to the scanning time of a horizontal scanning line. Output b of delay circuit 2 is applied to delay circuit 1a which has the same delay time as delay circuit 1, and outputs of delay circuits 1, 1a, 2a and 2b are synthesized in synthesizer circuit 3, and the amplitude is reduced to 1/4 by an attenuator. The output of delay circuit 2 is compared in comparator 5 where white level W and black level B are applied; and when the cell is decided as a faulty cell, switch 7 is closed and switch 6 is opened. COPYRIGHT: (C)1979,JPO&Japio

Information transfer confirmation system for computer network

Abstract: PURPOSE:To simplify the control for the units at the reception side and thus to ensure a high efficiency for the packet transfer by providing the answer request on the packet to be transmitted next in case the answer of the reception confirmation information is required from the reception side before reaching the fixed packet number of the reception side at the transmission side. CONSTITUTION:Packet transmission process mechanism 1 analyzes the information through analysis mechanism 2 and then carries out transmission 3 and packet holding 5 under the control of transmission procedure control mechanism 4; while packet reception process mechanism 6 performs transfer confirmation answer 8 and message assembling 9 under the control of transmission procedure control mechanism 7. In other words, the answer request given from the transmission side is detected at the reception side and then detects the prescribed packet number to answer the reception confirming information to the trnamission side. At the transmission side, the answer request is set up on the packet to be transmitted next in case the answer of the recetion confirming information sent from the reception side is required before reaching the prescribed packet number of the reception side. Thus, the reception confirming information is obtained quickly from the reception side. As a result, the control is simplified for the units of the reception side, thus ensuring a high efficiency for the packed transfer.

Multiplication circular bus system

Abstract: PURPOSE:To make flow every frame on the bus without any gap using a buffer whose virtual capacity changes against the variation of the station number which take part in a circular bus. In this way, an effect of variation due to a transmission delay on the bus xan be deleted.

A Comparison of Information Policies for Minimum Delay Routing Algorithms

Abstract: The problem of routing in a computer networks is dealt with by separating the information problem and the control problem. Several classes of information policies are examined, and numerical comparisons are made of their performance, using representative values of network parameters. Routing based on the expected values of delay, rather than actual values of delay, is shown to be superior to the other algorithms considered.

Satellite Packet Switching with Global Assignments and Batch Poisson Arrivals

Abstract: A satellite packet switching multiaccess model which employs a global scheduling assignment scheme is described and analyzed for batch Poisson arrivals. System performance in terms of buffer overflow probability and system delay is analyzed and simulated. The numerical results, presented in graphical form, indicate that the performance improves as the population size M increases. For large value of M the queueing delay decays approximately exponentially as the buffer length increases. Our results indicate that the system delay performance of our dynamic assignment (DA) algorithm is significantly better than that of a synchronous time-division multiplexing scheme.

Control System Performance with Coded State Feedback

Abstract: The error performance of a linear time-invariant plant, remotely controlled with constant-gain state feedback from a coded digital communications link, is considered. The effects of finite information rate, reliability, and delay are examined. While nonzero code transmission delay is generally deleterious to control system performance, it is shown that if the sampling period is specified, then block coding within each sample period may be beneficial. Numerical results are given for the case of a scalar plant

Modem interface control circuit

Abstract: PURPOSE:To avoid malfunction of the communication control caused by the transmission delay time by generating a transmissible pseudo signal between the communication control unit and the modem, and thus to eliminate the redundancy of the transmission capacity at the multiple transmission unit.

Interface communication processor for public packet switching network

Abstract: Promoted by the advancement of computer communication technology and social needs for data communications, many countries are setting up public data networks using mostly packet switching technology. Meanwhile, with the wide distribution of data communication service areas, interconnection of local networks and computers have become very important. Intercomputer communications through public data networks by means of packet switching are expected to become common in the future. In that case, the interfaces between the networks and subscriber terminals (i.e., DTE such as host computers and terminals) and the protocol are very inportant, and they contain many problems requiring solution.

Continuous variable type delay line

Abstract: PURPOSE:To improve the mounting efficiency of printed circuit board without using the fine tuning adjustment, by continuously changing the transmission delay time between the external terminals through the conductor pattern having distribution constant and the moving tip sliding on the conductor pattern.

Near optimal behaviour of the packet switching broadcast channel

Abstract: The subject of this paper is an adaptive control procedure for stabilizing and optimizing the performance of ALOHA-like slotted packet switching channels. We prove sufficient conditions, via a mathematical model of the adaptive procedure,under which the procedure stabilizes the channel. This procedure is based on "listening" to the silent periods of the channel and modifying the retransmission probabilities of the blocked terminals as a function of this measurement. The optimal choice of the parameters of the adaptive procedure is analysed and simulation results are given in order to illustrate its practical effect.