Browse Prior Art Database

DROPPED CALL DETECTION ALGORITHM

IP.com Disclosure Number: IPCOM000008294D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2002-Jun-04
Document File: 3 page(s) / 102K

Publishing Venue

Motorola

Related People

Dan Tayloe: AUTHOR [+3]

Abstract

The IRIDIUM@ system provides global cellular telephony coverage via a constellation of 66 satel- lites positioned in low earth orbit. In such a system, the primary ends of the call are normally a satellite providing a connection to the user on the ground and a telephone switch providing an interconnection into the PSTN (Public Switched Telephone Network). See Figure 1. Each of these entities can directly see their end of the call. As such, they can determine directly if a call resource is still being used and release the resources being used if the call is ended.

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Technical Developments

DROPPED CALL DETECTION ALGORITHM

by Dan Tayloe, Pate Armbruster and Jerome Ball

PROBLEM DESCRIPTION

  The IRIDIUM@ system provides global cellular telephony coverage via a constellation of 66 satel- lites positioned in low earth orbit. In such a system, the primary ends of the call are normally a satellite providing a connection to the user on the ground and a telephone switch providing an interconnection into the PSTN (Public Switched Telephone Network). See Figure 1. Each of these entities can directly see their end of the call. As such, they can determine directly if a call resource is still being used and release the resources being used if the call is ended.

  The problem in this network is that there is equipment in the middle, the Earth Terminal Controllers (ETCs), which communicates on the one hand with the satellites, and on the other hand with the telephone switches. The ETCs rely on messages from one end or the other to tell it that a call has ended so that it can free up the resources allocated to that call. If, due to network problems, these release messages are not received, the call resources can get permanently left in a hung state.

PROBLEM SOLUTION

The proposed solution to this problem is fairly simple. Given the natum of a satellite coverage in a

non-geosynchronous orbit, the observation was made that the call must experience a handoff from one satellite to another on a regular basis. For example, if the user 106 in Figure 2 does not experience a handoff from satellite 100 to satellite 101 within a reasonable period of time, it can be correctly assumed that the call has been terminated. In the IRIDIUM system which places satell...