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TRAFFIC CONGESTION CONTROL FOR THE IRIDIUMâ„¢ SYSTEM

IP.com Disclosure Number: IPCOM000006369D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2001-Dec-28
Document File: 2 page(s) / 108K

Publishing Venue

Motorola

Related People

Thomas J. Mihm: AUTHOR [+3]

Abstract

The IRIDIUM' system may be viewed as a space- based packet-switched communications network shown in Figures 1-4, augmented by ground nodes providing direct user interface either to an individual user or to a public switched telephone network. As such it provides delay and efficiency advantages characteristic of networks offering dynamic resource sharing. However, demands in excess of system capacity can induce congestion effects, rapidly eliminating the benefits of these inherent advan- tages. This results in reduced throughput, unfairness, and possible network deadlock Tiatlic control procedures most therefore be incorporated which monitor/limit system dynamic response during periods of heavy system usage. malfunction. This leads in a natural way to the defini- tion of three additional levels of flow control, shown in Figures 2-4.

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MOTOROLA /NC. Technical Developments Volume 15

May 1992

TRAFFIC CONGESTION CONTROL FOR THE IRIDIUM" SYSTEM

by Thomas J. Mihm, Steven H. Moritz, and Theresa Chen Yen Wang

  The IRIDIUM' system may be viewed as a space- based packet-switched communications network shown in Figures 1-4, augmented by ground nodes providing direct user interface either to an individual user or to a public switched telephone network. As such it provides delay and efficiency advantages characteristic of networks offering dynamic resource sharing. However, demands in excess of system capacity can induce congestion effects, rapidly eliminating the benefits of these inherent advan- tages. This results in reduced throughput, unfairness, and possible network deadlock Tiatlic control procedures most therefore be incorporated which monitor/limit system dynamic response during periods of heavy system usage.

malfunction. This leads in a natural way to the defini- tion of three additional levels of flow control, shown in Figures 2-4.

  Space-based transmission delay is key to both base- line service quality and trtic control performance. Under normal operating conditions, space-based message delay is rigorously controlled to maintain voice quality. Addi- tion of traffic control discipline to this process must be carefully balanced, since information exchange 16,18 in Figure 1 typically increases delay under light traffic load- ing, in exchange for reduced system degradation under heavy traffic conditions. Transmission delay in the IRIDIUM" system (not shown) is not large as com- pared to data rates. This renders practical implementa- tion of flow control via a multi-layered distributed protocol involving four different levels (or nodes), shown in Figures l-4.

  Figure 2 shows level 2 control, executed or directed by gateway 12. Gateway 12 has responsibiity for collecting real-time local traffic of packets 24. During periods of overload, gateway 12 uses such information to reject new calls or to terminate ongoing calls from subscriber unit segment 20 using directive 22, as required. Furthermore, gateway 12 service the subset of satellites 14 correspond- ing to a geographic area. This function includes issu- ance of directives 19 causing satellite 14 to implement backup cross-link routing algorithms, thereby leading cross-link transfer traffic to be routed...