Packet-switching in a slotted satellite channel

  • Authors:
  • Leonard Kleinrock;Simon S. Lam

  • Affiliations:
  • University of California, Los Angeles, California;University of California, Los Angeles, California

  • Venue:
  • AFIPS '73 Proceedings of the June 4-8, 1973, national computer conference and exposition
  • Year:
  • 1973

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Abstract

Imagine that two users require the use of a communication channel. The classical approach to satisfying this requirement is to provide a channel for their use so long as that need continues (and to charge them for the full cost of this channel). It has long been recognized that such allocation of scarce communication resources is extremely wasteful as witnessed by their low utilization (see for example the measurements of Jackson & Stubbs). Rather than provide channels on a user-pair basis, we much prefer to provide a single high-speed channel to a large number of users which can be shared in some fashion; this then allows us to take advantage of the powerful "large number laws" which state that with very high probability, the demand at any instant will be approximately equal to the sum of the average demands of that population. In this way the required channel capacity to support the user traffic may be considerably less than in the unshared case of dedicated channels. This approach has been used to great effect for many years now in a number of different contexts: for example, the use of graded channels in the telephone industry, the introduction of asynchronous time division multiplexing, and the packet-switching concepts introduced by Baran et al., Davies, and finally implemented in the ARPA network. The essential observation is that the full-time allocation of a fraction of the channel to each user is highly inefficient compared to the part-time use of the full capacity of the channel (this is precisely the notion of timesharing) We gain this efficient sharing when the traffic consists of rapid, but short bursts of data. The classical schemes of synchronous time division multiplexing and frequency division multiplexing are examples of the inefficient partitioning of channels.