{
  "patent_number": "US 5920821",
  "country": "US",
  "title": "How Phones Automatically Find and Update Network Lists Using CDPD",
  "original_title": "Use of cellular digital packet data (CDPD) communications to convey system identification list data to roaming cellular subscriber stations",
  "summary": "A 1995 system for helping mobile phones automatically update their preferred network lists and find the best service provider using a data-only channel.",
  "what_it_does": "The patent describes a method for mobile phones to stay updated on which cellular networks they should use without manual input. It uses a specific data channel called CDPD to broadcast a version number for a list of preferred service providers. The phone compares this broadcasted version number to the one it already has stored. If the numbers do not match, the phone automatically downloads the updated list over the CDPD channel, ensuring it always knows which local networks are available and preferred for roaming.",
  "what_it_does_not_cover": [
    "Does not cover updates delivered over standard voice channels or SMS.",
    "Does not cover modern 4G/LTE or 5G network selection protocols.",
    "Does not cover methods for updating firmware or OS software, only network identification lists.",
    "Does not cover manual network selection by the user via a settings menu."
  ],
  "filed": "1995-12-04",
  "granted": "1999-07-06",
  "expires": "2015-12-04",
  "status": "expired",
  "holder": "Bell Atlantic Network Services Inc",
  "holder_url": "https://patentbrief.org/company/bell-atlantic-network-services-inc",
  "inventors": [
    {
      "name": "John W. Seazholtz",
      "url": "https://patentbrief.org/inventor/john-w-seazholtz"
    },
    {
      "name": "Robert D. Farris",
      "url": "https://patentbrief.org/inventor/robert-d-farris"
    }
  ],
  "times_cited": 179,
  "tags": [
    "telecommunications",
    "mechanical"
  ],
  "abstract": "An analog cellular voice telephone system and subscriber stations associated therewith are controlled to conserve power and to provide alternate service carriers. Acquisition of all of the service carriers is facilitated through the use of system identification numbers (SIDs) associated with each service carrier. A roaming subscriber will tune to a cellular digital packet data (CDPD) frequency to obtain a list of service carriers operating within that geographical area. Based upon a comparison with a preferred SID list stored in the subscriber station, an available service carrier will be selected by the subscriber station, and registration with the selected service carrier will take place. Usually, analog voice communication is suspended until the selection process takes place.",
  "url": "https://patentbrief.org/patent/us/5920821/use-of-cellular-digital-packet-data-cdpd-communications-to-convey-system-identification-list-data-to-roaming-cellular-subscriber-stations",
  "markdown_url": "https://patentbrief.org/patent/us/5920821/use-of-cellular-digital-packet-data-cdpd-communications-to-convey-system-identification-list-data-to-roaming-cellular-subscriber-stations/md",
  "google_patents_url": "https://patents.google.com/patent/US5920821",
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}