Browse Prior Art Database

METHOD FOR MINIMIZING SUBSCRIBER ROAMING DURING MASTER SITE FAILURE

IP.com Disclosure Number: IPCOM000009768D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-17
Document File: 3 page(s) / 168K

Publishing Venue

Motorola

Related People

James E. Streed: AUTHOR

Abstract

Today's multi-site, multi-zone ASTRO systems use a number of techniques to ensure that subscribers remain in wide area coverage whenever possible. When a site enters site trunking mode, the subscribers registered to that site try to find another site that is in wide area mode. If the site enters site trunking mode because of a Zone Controller failure, all of the sites will be in site trunking mode, but the subscribers will still roam. After the system returns to wide area mode, the subscriber registration information has to be reconciled, which delays the return of full system service availability.

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MOTOROLA

Technical Developments

METHOD FOR MINIMIZING SUBSCRIBER ROAMING DURING MASTER SITE FAILURE

by James E. Streed

BACKGROUND

Today's multi-site, multi-zone ASTRO systems use a number of techniques to ensure that subscribers remain in wide area coverage whenever possible. When a site enters site trunking mode, the subscribers registered to that site try to find another site that is in wide area mode. If the site enters site trunking mode because of a Zone Controller failure, all of the sites will be in site trunking mode, but the subscribers will still roam. After the system returns to wide area mode, the subscriber registration information has to be reconciled, which delays the return of full system service availability.

In today's systems (ASTRO 25 Release 5.0), subscribers not programmed as " Always Preferred" will seek out a wide area site when the site to which they are registered enters site trunking mode. Each site transmits information on the state of adjacent sites (Adjacent Status Broadcast - ASB) so that the subscribers know where to roam to look for a wide area site.

The site controller receives the adjacent site status information from the Zone Controller. When the site enters site trunking mode because of a loss of communication with the Zone Controller, the site controller continues to transmit the last known adjacent site statuses, but the site controller sets a bit that indicates to the subscribers that the adjacent site statuses may be invalid.

When a significant failure occurs at the master site, such as a Zone Controller reset, all sites in the zone will be in site trunking mode. Each site will transmit the last known status of its adjacent sites, which will indicate wide trunking, and will set the ASH "invalid" bit. After its Failure Recovery Hold Off Timer (FRHOT) expires, a subscriber that is not programmed as " Always Preferred" roams to an adjacent site whose last known state was wide

Motorola, Inc. 2000

trunking. The purpose of FRHOT is to keep subscribers at a site in site trunking mode for a short period of time in case the reason for site trunking was something transient, such as a link fade. Since the reason for site trunking was a master site failure, all of the sites will be in site trunking mode. The subscribers will continue to roam to other sites to try to find a wide area site.

After the master site failure has been resolved, the sites will start to return to wide area mode. Once the subscriber has realized that it is listening to a wide area site, the subscriber starts its Random Recovery Hold Off Timer (RRHOT). The RRHOT prevents subscribers from registering or returning to a wide area site all at once, which would flood the control channel.

If the wide area site traJ1smits an ASB with the invalid bit cleared indicating that the site with which the subscriber had last registered is now in wide area mode, and the subscriber's RRHOT has not expired, the subscriber will return to the site with which it h...