Browse Prior Art Database

HANDOFF INTERLOCK IN A PACKET BASED SV NETWORK

IP.com Disclosure Number: IPCOM000008897D
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2002-Jul-22
Document File: 2 page(s) / 119K

Publishing Venue

Motorola

Related People

James P. Redden: AUTHOR [+3]

Abstract

This paper describes a solution to a pack routing problem faced in a satellite based cellular system. An algorithm is described which is used to prevent fatal packet routing race conditions that can occur due to the mobile stations handing off from satellite to satellite.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 2

0 M M0roR0LA

Technical Developments

HANDOFF INTERLOCK IN A PACKET BASED SV NETWORK

by James P. Redden, Michael Krutz and Daniel R. Tayloe

ABSTRACT

system, in the specific situation of a mobile station to mobile station call, bringing the packets from both halves of the call down to a common point on the earth can introduce a significant amount of delay. In this case, it is much more desirable to send packets directly from one mobile station over the space network and back down to the second mobile station without an intervening, stable anchor point, such as a cellular switch. In the IRIDIUM@ net- work, the cellular switching equipment on the ground is referred to as a gateway (GW).

  In this environment, a mobile-station-to-mobile- station call will cause problems when both mobile stations attempt to handoff at the same time. Race conditions will exist where a change at one end can be missed. This could cause packets from one of the two mobile stations to get routed to the wrong place, causing a one way audio situation to exist until the two users decide to end the call. INVENTION DESCRIPTION

  We have developed a method to ensure that at least one end of a call is stabile when a handoff takes place. In a preferred embodiment of this invention, an interlock mechanism is provided at the gateways controlling either end of the call to prevent fatal packet routing race conditions that could occur dur- ing handoff conditions. Alternatively, the arbitration could be executed through the SVs at either end of the call or at the mobile stations themselves.

  In this invention, when a mobile station at a first end of a call needs to handoff, it signals its visited gateway concerning the need for handoff. That gateway in turn requests of the far end gateway con- trolling a second end of the call a handoff lock on the second end of the call. This handoff lock is used to prevent the second end from handing off until the first end finishes its handoff.

  This paper describes a solution to a pack routing problem faced in a satellite based cellular system. An algorithm is described which is used to prevent fatal packet routing race conditions that can occur due to the mobile stations handing off from satellite to satellite.

PROBLEM ENCOUNTERED

  Managing handoff for the IRIDIUM@ satellite based packet network is a bit different from a nor- mal ground based cellular system. In a ground based system, additional system delay due to the propagation delay between different pieces of the network is negligible compared to unavoid- able delays such as speech framing, vocoder encod- ing/decoding, etc.

  Consider for a moment the speech path of ground based cellular telephony system for the case of a mobile station to...