How Phones Automatically Find and Update Network Lists Using CDPD
A 1995 system for helping mobile phones automatically update their preferred network lists and find the best service provider using a data-only channel.
Original patent title: “Use of cellular digital packet data (CDPD) communications to convey system identification list data to roaming cellular subscriber stations”
A 1995 system for helping mobile phones automatically update their preferred network lists and find the best service provider using a data-only channel. Granted to Bell Atlantic Network Services Inc in 1999 with 24 claims and 179 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
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.
The gap
What does this patent 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.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
Instead of forcing the phone to scan every single frequency to find a network, the system broadcasts a tiny version number on a dedicated data channel to tell the phone exactly when an update is needed.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Early analog cellular roaming
Automated network provider list updates
Why it matters
The bigger picture
Before this technology, roaming phones often struggled to find service or wasted battery power scanning every possible frequency. This patent provided a way to offload that intelligence to a data channel, which was a vital step toward the seamless roaming experience modern users expect today.
Filed
December 4, 1995
Granted
July 6, 1999
Market context
Who's building on this
Companies in this space
The core logic of using a dedicated data stream to manage device configuration is now standard practice for all major cellular carriers and device manufacturers like Apple and Samsung. While the specific CDPD technology is obsolete, the concept of 'over-the-air' (OTA) provisioning for network settings remains fundamental.
Market impact
This patent helped standardize how mobile devices manage roaming and network discovery during the transition from analog to early digital cellular systems. It reduced the operational burden on cellular networks by preventing thousands of phones from constantly scanning for service in inefficient ways.
Claim 1 — Plain English
What this patent covers
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.
The clever bit
Instead of forcing the phone to scan every single frequency to find a network, the system broadcasts a tiny version number on a dedicated data channel to tell the phone exactly when an update is needed.
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.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
Moderate
Citation count
40/40
Highly cited
Claim breadth
16/20
Broad claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assigneeassigneeThe entity that owns the patent — usually the inventor's employer or a company.Read more →
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$102K – $328K
Midpoint $205K · expired or expiring · industry ×1.4
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
24 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Seazholtz, J. W., & Farris, R. D. (1999). How Phones Automatically Find and Update Network Lists Using CDPD (U.S. Patent No. 5,920,821). U.S. Patent and Trademark Office. 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
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does How Phones Automatically Find and Update Network Lists Using CDPD cover?
A 1995 system for helping mobile phones automatically update their preferred network lists and find the best service provider using a data-only channel.
Who owns patent US 5920821?
Bell Atlantic Network Services Inc owns this patent, granted in 1999.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 5920821 cited by?
This patent has been cited by 179 later patents that build on its ideas.
What problem does this patent solve?
Before this technology, roaming phones often struggled to find service or wasted battery power scanning every possible frequency. This patent provided a way to offload that intelligence to a data channel, which was a vital step toward the seamless roaming experience modern users expect today.
What does this patent NOT cover?
Does not cover updates delivered over standard voice channels or SMS.
Patent monitoring