• An Analysis of a Tandem Queueing System for Flow Control in Computer Networks

      Chu, W. W.; Faylolle, G.; Hibbits, D.; University of California, Los Angeles; I.R.I.A. (International Foundation for Telemetering, 1978-11)
      A tandem queueing system with constant service times and threshold control is modeled and analyzed in this paper. The input to the first queue is controlled by the buffer occupancy of the second queue. When the second queue has more than No customers, the input to the first queue will be rejected. The input to the second queue consists of the output from the first queue and an external input which is assumed to be Poisson distributed. The behavior of such a queueing system is analyzed and portrayed in graphs. The threshold control rejects input traffic to the first queue and avoids congestion at the second queue. As a result, the delay for an arrival to be serviced by both of the queues is much lower than the case without threshold control. As N₀ increases, the system behavior approaches the case of the system without threshold control. Such a queueing model is motivated by congestion control in a computer network. An example is given to illustrate the applications.
    • Hybrid Packet and Circuit Data Networks: Design and Operation Issues

      Gerla, Mario; University of California, Los Angeles (International Foundation for Telemetering, 1978-11)
      Experience with packet switching during the past decade has shown that the packet technology is very cost effective for bursty communications between computers and terminals. However, for applications characterized by a steady instead of bursty flow of information (e.g., file transfer, digitized speech, facsimile), it has been established that pure packet protocols are often inadequate because of the unnecessarily high line overhead and the high delay fluctuations between consecutive packets [1]. For such applications, a circuit switching approach (either physical or virtual) appears more advantageous [1],[2]. In the physical circuit approach, bandwidth is dedicated to a connection for the entire duration of the session; while in the virtual circuit approach the path is fixed at the beginning of the session and some expected bandwidth is guaranteed, in a statistical sense, along the path (but no physical bandwidth is assigned).
    • On the Combined Performance of Joint Access Control/Modulation/Coding Schemes

      Rubin, Izhak; University of California, Los Angeles (International Foundation for Telemetering, 1978-11)
      The combined performance of a multi-access communication channel under joint access control/modulation/coding procedures is examined. The multi-access channel serves as a shared information transmission medium in a data communication network, such as a satellite, computer or terrestrial radio communication network. The performance of the underlying modulation/coding scheme is expressed in terms of the corresponding bit-error probability vs. signal-to-noise ratio curve. The computational cutoff error rate is also used as a proper performance measure characterizing the joint modulation/coding scheme. The performance of the underlying access-control algorithm is described by the message-delay vs. network-throughput curve. Integrating these performance functions, the combined performance of the joint access-control/modulation/coding procedure is derived. In particular, under proper bandwidth and power limitations, one can then evaluate the total amount of information that can be transmitted through the channel, in a reliable and timely fashion, at prescribed bit-error-probability and message-delay values, under various communication link, transceiver, repeater and antenna conditions.
    • Processing Satellites

      Omura, Kim; University of California, Los Angeles (International Foundation for Telemetering, 1978-11)
      With few exceptions, satellite communications systems today employ conventional nonprocessing satellites that are often referred to as "bent pipes in the sky." These satellites merely act as nonlinear (TWT) amplifiers that transmit on the downlink the same signals plus noise (frequency shifted) that it receives on the uplink. It is now clear that the "micro-processor revolution" will impact on satellite technology and result in a new generation of communication satellites with various on-board digital processing. The orbiting experimental military satellites Les-8/9 are the first-of the new generation of processing satellites. Many more such satellites are now being considered with increasingly complex digital processing on the satellites. For military applications these on-board processing capabilities are listed below in increasing order of complexity.