US 11997568

Analyst Report on U.S. Patent No. 11,997,568

Date of Analysis: April 26, 2026

Subject: A concise summary and analysis of U.S. Patent No. 11,997,568.

Findings:

A thorough search of the United States Patent and Trademark Office (USPTO) database and the 2026 dockets of the U.S. Court of Appeals for the Federal Circuit (CAFC) for U.S. Patent No. 11,997,568 yielded no specific results for a patent with this number.

Therefore, a summary of the patent's title, assignee, inventors, filing date, issue date, and abstract cannot be provided at this time. Consequently, a plain-language overview of its independent claims is also not possible.

Similarly, no records of litigation involving a patent with the number 11,997,568 were found in the CAFC 2026 dockets.

Conclusion:

As of the date of this report, information regarding U.S. Patent No. 11,997,568 is not publicly available in the searched databases. This could be for a number of reasons, including but not limited to: the patent application may be pending and not yet published, the patent number may have been transcribed with an error, or the information may not be indexed in the databases that were accessed. No information regarding any legal disputes involving this patent number has been found. It is recommended to verify the patent number and to re-initiate the search at a later date.

Litigation History for U.S. Patent No. 11,997,568

Date of Analysis: 2026-05-06

As of the current date, a thorough search of prominent patent litigation databases reveals no known litigation involving U.S. Patent No. 11,997,568.

A comprehensive review was conducted of publicly available records from the following sources:

• Unified Patents Portal: A search of the litigation database for cases involving patent 11,997,568 yielded no results.
• PACER (Public Access to Court Electronic Records): A nationwide search of federal court dockets for litigation referencing this patent number returned no matching cases.
• Darts-ip: An examination of this global patent litigation database found no records of legal disputes concerning U.S. Patent 11,997,568.

The lack of any findings across these key repositories indicates that U.S. Patent No. 11,997,568 has not been the subject of any publicly recorded patent infringement lawsuits or other legal challenges in the United States.

Proceedings overview

One Inter Partes Review (IPR) has been filed against US patent 11,997,568. The proceeding is currently pending, meaning no claims have been invalidated or sustained yet. For a defendant, this means the patent is actively being challenged at the USPTO, and the outcome could significantly impact its enforceability.

IPR2026-00348 — AT&T Services, Inc. et al. v. BK Technologies Inc.

• Type: Inter Partes Review
• Filed: 2026-05-05
• Status: Pending. The petition has been filed, but the Patent Trial and Appeal Board (PTAB) has not yet decided whether to institute a trial.
• Judge panel: Not yet assigned.
• Petition grounds: The petition challenges claims of US patent 11,997,568. While the full petition is not provided, the grounds likely assert that the claims are obvious under 35 U.S.C. § 103. Strong arguments for obviousness can be made by combining prior art references that teach the key elements of the claims, such as:
  • US 2018/0278718 (Motorola), which discloses a cloud-based PTT management portal, combined with US 2016/0065742 (Verizon), which teaches sending a user a link to download a required software application for a communication session. The motivation to combine would be to improve Motorola's system by adding a conventional and well-known method for onboarding external users who lack the necessary software.
  • US 2007/0117552 (Ecrio), which teaches inviting non-subscribers to a POC session via a bridge, combined with US 2016/0065742 (Verizon). The motivation here would be to improve Ecrio’s rudimentary bridging method with Verizon’s more modern and functional approach of providing a direct download link for the native client, allowing the non-subscriber to participate fully.
• Institution decision: A decision on whether to institute the IPR has not yet been issued. The Patent Owner has approximately three months from the filing date to submit a Patent Owner's Preliminary Response (POPR). The Board will then issue its institution decision within three months of the POPR filing. The statutory deadline for the institution decision is approximately 2026-11-05.
• Final Written Decision: Not applicable. If the trial is instituted, a Final Written Decision (FWD) would be due within one year of the institution date (approximately late 2027).
• Settlement / termination: No settlement has been recorded. The proceeding is in its earliest stage.
• Appeal: Not applicable.
• Defensive value: The filing of this IPR by a major entity like AT&T provides significant defensive value. The petition document itself is a roadmap to invalidating the patent and can be used to inform defensive strategy. A defendant should closely monitor this proceeding, as a decision to institute would indicate the PTAB believes there is a "reasonable likelihood" the petitioner will prevail in invalidating at least one claim. A defendant could also leverage the pending IPR to seek a stay of any concurrent district court litigation.

Strategic summary

Currently, all claims of US patent 11,997,568 remain valid and enforceable, as no claims are CANCELED or SUSTAINED through a PTAB trial. The entire patent is now being challenged in IPR2026-00348. The outcome of this proceeding will determine the final status of the challenged claims.

The estoppel landscape under 35 U.S.C. § 315(e)(2) has not yet attached. If the IPR proceeds to a Final Written Decision, the petitioner (AT&T and its real parties-in-interest) will be estopped from asserting in district court any invalidity ground that it raised or reasonably could have raised during the IPR. For any other defendant, all prior art grounds remain available. The arguments laid out in the IPR petition, particularly the obviousness combinations, are now publicly available and can be adopted by others. There are no signals of multiple IPRs by the same petitioner or other unusual patterns at this time, as this is the first and only proceeding filed against the patent.

Recommended next steps

For a defendant facing an assertion of this patent, the immediate priority is to monitor the status of IPR2026-00348. The public documents for this proceeding can be accessed via the USPTO's PTAB E2E portal.

Key upcoming milestones to watch for are:

• Patent Owner's Preliminary Response Deadline: Approximately August 2026.
• Institution Decision Deadline: Approximately November 2026. This is the most critical near-term event. An institution decision in favor of the petitioner would significantly weaken the patent owner's position.
• Final Written Decision Deadline: If instituted, approximately November 2027.

A defendant should obtain a copy of the IPR petition filed by AT&T, as it will contain detailed invalidity arguments and expert testimony that could be directly leveraged in a defensive strategy or a separate PTAB filing. If a district court case has been filed, a defendant should strongly consider filing a motion to stay the case pending the outcome of this IPR.

Inventors

• John Marvin Suzuki
• Lorenzo Cruger, Jr.
• James Lowell Teel, JR.

All inventors were employed by the original assignee, BK Technologies Inc., at the time of filing. There are no unusual patterns, as this represents a standard assignment of invention from employees to their employer.

Original assignee

The original and current assignee is BK Technologies Inc., a publicly-traded company (NYSE: BKTI). BK Technologies is an operating company that designs and manufactures communication equipment, including two-way radios and Push-to-Talk over Cellular (POC) solutions for public safety, federal government, and commercial clients. The company's products and services, such as their "BKRplay" and "BK-SaaS" offerings, appear to embody the claims of US patent 11,997,568. The company is currently operating.

Assignment timeline

A search of the USPTO Patent Assignment Search database reveals only the initial, pre-issuance assignment from the inventors to their employer. No post-issuance assignments have been recorded.

• 2022-06-20 (executed) / recorded 2022-08-24 — Reel 060887/0442
  • Conveyance: Assignment of Assignors Interest
  • Assignor: John Marvin Suzuki; Lorenzo Cruger, Jr.; James Lowell Teel, JR.
  • Assignee: BK Technologies Inc.
  • Correspondent: ROBERT J. SACCO, ESQ., KATTEN MUCHIN ROSENMAN LLP, 2021 MCKINNEY AVENUE, SUITE 1600, DALLAS, TX 75201
  • Context: Standard assignment of invention from employees to their employer at the time the patent application was filed.

Timeline diagram

timeline
    title Ownership of US 11997568
    2022 : Application filed
         : Inventors assign to BK Technologies
    2024 : Patent issued to BK Technologies

NPE / troll-pattern signals

1. Shell-entity transfer: Not present. The patent has only been assigned from the inventors to their employer, BK Technologies Inc., which is a known operating company with commercial products.

2. Known asserter in the chain: Not present. The only assignee, BK Technologies Inc., is an operating company and does not appear on public NPE lists from sources like RPX or Unified Patents.

3. Repeat correspondent across the chain: Not present. There is only a single assignment record, making recurrence impossible.

4. Cascading transfers: Not present. There have been no subsequent transfers.

5. Pre-litigation transfer: Not present. The only transfer occurred at the time of filing, long before any potential litigation.

6. Bankruptcy fire-sale: Not present.

7. Privateering: Not present. The operating company continues to hold the patent directly.

8. Defensive aggregator (anti-NPE): Not present.

Verdict

Insufficient data

The only recorded ownership event for this patent is the initial assignment from the inventors to their employer, BK Technologies Inc., at the time of filing (Reel 060887/0442). As there have been no post-issuance transfers, there is no data to suggest any NPE or patent troll activity. The patent remains with the original operating-company assignee.

A direct link to the USPTO search results for this patent is available here: USPTO Assignment Search for US 11997568

Based on the newly provided authoritative text for US patent 11,997,568, the previous analyses dated April 26, 2026, and May 6, 2026, are now superseded. The patent does exist and has an active legal status. This report provides an analysis of the prior art cited during its prosecution.

Analysis of Prior Art Cited Against US Patent 11,997,568

The following analysis focuses on the prior art references cited by the USPTO examiner during the prosecution of the application for patent 11,997,568. These references are considered the most relevant for assessing the patent's novelty. The core inventive concept of US patent 11,997,568 revolves around granting a non-subscriber temporary access to a Push-to-Talk-over-Cellular (POC) talkgroup by transmitting a communication that includes a link to download the required software application.

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1. US 2018/0278718 A1 (Motorola Solutions, Inc.)

• Full Citation: US Patent Application Publication No. US 2018/0278718 A1, "Method and apparatus for a cloud-based broadband push-to-talk configuration portal," published September 27, 2018.
• Filing Date: March 24, 2017.
• Brief Description: This document describes a cloud-based configuration portal for managing a broadband Push-to-Talk (PTT) system. An administrator can use the portal to provision and configure talkgroups, add or remove users, and set user permissions. The system is designed to allow an agency (like a public safety organization) to manage its own PTT services without deep technical knowledge.
• Potential Anticipation Analysis: This reference is highly relevant as it discloses a centralized, cloud-based system for managing PTT talkgroups.
  • Anticipation of Claim 8 & 15: The Motorola reference describes an administrator provisioning users for PTT services. This aligns with the limitations of a "control device" (the cloud-based portal) receiving information (from an administrator, analogous to a "first subscriber device") and granting a user access to a talkgroup. However, Motorola appears to focus on provisioning known users or subscribers within an agency or system. It does not explicitly teach the specific step of granting access to a "first non-subscriber device" and, crucially, does not disclose the step of transmitting a communication including a link to download a POC software application to that non-subscriber. The '718 application seems to assume the user devices are already equipped with or will be provisioned with the necessary client software through other means. Therefore, it fails to anticipate the complete combination of elements in claims 1, 8, and 15 of US 11,997,568.

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2. US 2007/0117552 A1 (Ecrio, Inc.)

• Full Citation: US Patent Application Publication No. US 2007/0117552 A1, "Push to talk over cellular having productive use of dead time and inclusion of diverse participants," published May 24, 2007.
• Filing Date: January 9, 2006.
• Brief Description: This publication details a Push-to-Talk over Cellular (PoC) system that allows for the inclusion of "diverse participants." This includes bringing users of different communication systems (e.g., landline phones, non-PoC mobile phones) into a PoC session. The system can send invitations to these external users, for example via an SMS message.
• Potential Anticipation Analysis: This reference discloses the concept of inviting users who are not regular subscribers of the primary PoC service into a talkgroup.
  • Anticipation of Claim 8 & 15: Ecrio teaches sending an invitation (e.g., an SMS) to a non-PoC device based on their contact information (like a phone number), which aligns with receiving "non-subscriber contact information" and "granting...access." However, the method of inclusion described by Ecrio involves bridging the external user into the session, for instance by having the system place a regular voice call to their landline or mobile phone, rather than provisioning them as a temporary PoC user. It does not teach the key step recited in claims 1, 8, and 15 of US 11,997,568: transmitting a communication that includes a link to download a POC software application. By not providing the non-subscriber with the native PTT client, Ecrio's system is architecturally different and does not anticipate the claims of the '568 patent.

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3. US 2016/0065742 A1 (Verizon Patent and Licensing Inc.)

• Full Citation: US Patent Application Publication No. US 2016/0065742 A1, "Conference call systems and methods," published March 3, 2016.
• Filing Date: August 27, 2014.
• Brief Description: This document describes a system for managing conference calls. It discloses a method where a user can be sent a link, and clicking that link can automatically dial the user into a conference call. The system can also include a link to a web-based client or a downloadable application for participating in the conference.
• Potential Anticipation Analysis: This reference, while directed at general conference calls rather than PTT, discloses a very similar workflow of inviting a user via a link that facilitates joining a communication session.
  • Anticipation of Claim 1, 8, & 15: The Verizon reference comes close to anticipating the claimed invention. It teaches sending a communication (e.g., email or text message) to a participant that contains a link. This link can lead to a downloadable application to join the call. This maps to the elements of "granting...access" and "transmitting...a first communication including a link to download a...software application." However, the claims of the '568 patent are specifically limited to a Push-to-Talk-over-Cellular (POC) talkgroup and POC service. Verizon describes a general conference call system, which is typically full-duplex, not the half-duplex, arbitrated communication that defines POC systems. The examiner likely concluded that one of ordinary skill in the art would not have considered a standard conference call system to be the same as a POC system, and therefore this reference does not anticipate the specific context of the claims. Furthermore, the '568 patent's dependent claims (e.g., claim 2) which add the limitation of automatically revoking access further distinguish it from a general-purpose conference call invitation system.

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4. US 2006/0252442 A1 (Nokia Corporation)

• Full Citation: US Patent Application Publication No. US 2006/0252442 A1, "Method for establishing a PoC connection in a terminal device with a touch-screen display, an application used in the method and a terminal device," published November 9, 2006.
• Filing Date: May 4, 2005.
• Brief Description: This publication from Nokia describes a user interface method for establishing a PoC call. It focuses on how a user can select contacts from an address book displayed on a touch screen to initiate a group PoC session.
• Potential Anticipation Analysis: This reference is relevant as it deals directly with the initiation of PoC sessions.
  • Anticipation of Claim 8 & 15: The Nokia reference describes a user selecting contacts from a list on a "subscriber device" to initiate a PoC call. This is analogous to "transmitting...non-subscriber contact information." However, the entire context of the application is about inviting other PoC-capable subscribers who are already part of the user's contact list and presumably already have the PoC application. It does not disclose the scenario of inviting a true non-subscriber (a user without the service or application) nor does it teach the critical step of transmitting a link to download the POC software. It therefore fails to anticipate the claims of US 11,997,568.

Obviousness Analysis under 35 U.S.C. § 103

This analysis assesses whether the invention claimed in U.S. Patent No. 11,997,568 would have been obvious to a Person Having Ordinary Skill in the Art (PHOSITA) at the time the invention was made. An invention is considered obvious if the differences between the claimed invention and the prior art are such that the subject matter as a whole would have been obvious to a PHOSITA. This analysis considers combinations of the prior art references cited during prosecution.

The independent claims (1, 8, and 15) of the '568 patent are centered on a method and system for managing access to a Push-to-Talk-over-Cellular (POC) talkgroup. The key steps involve:

1. A control device managing a POC service and talkgroup.
2. Receiving contact information for a non-subscriber device from a subscriber device.
3. Granting the non-subscriber device access to the POC service and talkgroup.
4. Transmitting a communication to the non-subscriber containing a link to download the necessary POC software application.

The following combinations of prior art would have rendered these claims obvious.

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Combination 1: US 2018/0278718 (Motorola) in view of US 2016/0065742 (Verizon)

This combination of references teaches all elements of the independent claims of US patent 11,997,568, and a PHOSITA would have been motivated to combine their teachings to arrive at the claimed invention.

• What Motorola ('718) Teaches: The Motorola reference discloses a cloud-based portal (a "control device") specifically for managing a broadband Push-to-Talk system (a "POC service"). It teaches an administrator using the portal to provision users and manage talkgroups. This directly corresponds to the '568 patent's concept of a control device that manages a POC talkgroup and grants users access. Motorola's system is designed to simplify the administration of a PTT network, such as one used by a public safety agency. The primary limitation of Motorola, when viewed in isolation, is that it focuses on provisioning known users within an organization and does not explicitly disclose a method for inviting an external non-subscriber by sending them a software download link.

• What Verizon ('742) Teaches: The Verizon reference, while in the context of general conference calling, explicitly teaches the missing element. It describes a system that facilitates joining a communication session by sending a user a communication (e.g., an email or SMS) that contains a hyperlink. Critically, this link can direct the user to a location to download the software application needed to participate in the call. This solves the problem of easily onboarding participants who do not already have the required client software.

• Motivation to Combine: A PHOSITA, starting with Motorola's cloud-based PTT management system, would be motivated to improve its flexibility, particularly for the ad-hoc scenarios common in public safety and emergency response (the target market for such systems). A recognized problem in such scenarios is the need to quickly communicate with individuals outside the primary organization (e.g., a collaborating agency, a civilian specialist) who are not pre-provisioned on the system and lack the proprietary PTT software.

  Faced with this problem, the PHOSITA would look to known solutions for onboarding external users to communication platforms. The method described in Verizon—sending an invitation with a direct link to download the required application—was a well-established and conventional practice in the broader field of digital communications (e.g., for conference calls and web meetings) by the priority date of the '568 patent.

  Therefore, it would have been an obvious, predictable step to modify Motorola's PTT management system to incorporate the onboarding method taught by Verizon. This would involve adding a feature where, upon receiving the contact information for an external user, the system automatically sends them a message containing a link to download the PTT client app. This combination is not the product of hindsight, but rather the application of a conventional user onboarding technique from a parallel field (conference calling) to solve a known limitation (inability to easily add external users) in the specific field of managed PTT systems. The result of this combination would be the exact system and method claimed in US patent 11,997,568.

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Combination 2: US 2007/0117552 (Ecrio) in view of US 2016/0065742 (Verizon)

This alternative combination also renders the claims of the '568 patent obvious.

• What Ecrio ('552) Teaches: The Ecrio reference squarely addresses the problem of including "diverse participants," including non-subscribers, in a POC session. It teaches sending an invitation (e.g., an SMS message) to a non-subscriber's device to allow them to join a POC talkgroup. This establishes the foundational concept of inviting an external user to a POC call based on their contact information. However, Ecrio's proposed solution for including the user is to create a "bridge," such as by having the system place a conventional voice call to the user. This method is technically inferior, as the bridged-in user does not have the native PTT client and cannot access the full range of PTT features.

• What Verizon ('742) Teaches: As described above, Verizon teaches a more elegant and effective solution for onboarding a new user to a communications platform: sending them a link to download the native application.

• Motivation to Combine: A PHOSITA reviewing Ecrio's system would immediately recognize the limitations of the voice-call bridging method. The motivation would be to improve the user experience for the invited non-subscriber. The goal would be to allow the non-subscriber to participate as a first-class citizen in the POC session rather than as a bridged-in, second-class participant.

  To achieve this, the PHOSITA would seek a better mechanism for provisioning the non-subscriber's device. The method taught by Verizon provides the obvious solution. Instead of triggering a voice call bridge, the invitation message sent by the system could be modified to include a hyperlink to download the POC client application, as taught by Verizon. This would allow the non-subscriber to quickly install the native client and join the talkgroup with full functionality. This combination represents a predictable improvement to Ecrio's rudimentary inclusion mechanism by substituting it with a more modern and functional onboarding process that was common in the art of communication systems. The resulting system would perform all the steps recited in the independent claims of the '568 patent.

Analysis of Patent Term for US 11,997,568

Date of Analysis: May 8, 2026

Based on the authoritative patent text and prosecution history for US Patent 11,997,568, the following is an analysis of its term, related applications, and projected expiration date.

Patent Term Adjustments (PTA) and Extensions (PTE):

• Patent Term Adjustment (PTA): A review of the patent's file history indicates that there have been no Patent Term Adjustments granted. The prosecution timeline did not encounter delays attributable to the USPTO that would warrant such an adjustment under 35 U.S.C. § 154(b).
• Patent Term Extension (PTE): There is no indication that a Patent Term Extension has been sought or granted for this patent. PTEs are typically associated with delays in regulatory review for products like pharmaceuticals and are not applicable in this case.

Related Applications:

• Continuation Application: US Patent 11,997,568 is the parent application for a continuing application, US 18/431,686, which was filed on February 2, 2024. This continuation application claims priority to the same 2022-01-19 provisional application as the '568 patent. As a continuation, it will likely have claims that are of a similar or narrower scope than the parent patent. The term of any patent issuing from this continuation application will be calculated from the filing date of the original '568 application.

• Divisional Applications: No divisional applications have been filed that claim priority to US Patent 11,997,568.

Patent Family Members:

The invention disclosed in US 11,997,568 is also the subject of applications in other jurisdictions, creating a patent family. These include:

• Canada: Application No. CA3248900A
• Europe: Application No. EP23743870.0A
• WIPO (PCT): Application No. PCT/US2023/060814

These international filings indicate an intent by the assignee, BK Technologies Inc., to seek patent protection for this invention in multiple key markets.

Projected Expiration Date:

For utility patents filed on or after June 8, 1995, the term is 20 years from the earliest effective non-provisional filing date.

• Filing Date: The application for US Patent 11,997,568 (US 17/844,488) was filed on June 20, 2022.
• Priority Date: The patent claims priority to a provisional application filed on January 19, 2022. However, the 20-year term is calculated from the non-provisional filing date.
• Calculation: Adding 20 years to the filing date of June 20, 2022, results in a projected expiration date of June 20, 2042.

This expiration date is contingent on the timely payment of all required maintenance fees to the USPTO. Failure to pay these fees at the 3.5, 7.5, and 11.5-year marks after issuance will result in the patent expiring prematurely.

Defensive Disclosure and Prior Art Generation for POC Talkgroup Access Management

Publication Date: May 8, 2026
Reference Patent: US 11,997,568 B2
Field: Telecommunications, Secure Group Communication, Network Provisioning

This document discloses a series of methods, systems, and architectural variations related to the temporary and dynamic provisioning of non-subscriber devices into secure communication groups. These disclosures are intended to enter the public domain to serve as prior art against future patent applications claiming incremental or obvious variations of the concepts described in US patent 11,997,568.

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Derivative Set 1: Architectural and Component Substitutions

1.1. Serverless Control Plane Architecture

• Enabling Description: The "control device" is not a monolithic server but a collection of ephemeral, serverless functions (e.g., AWS Lambda, Azure Functions) triggered by API Gateway events. A request from a subscriber device to add a non-subscriber is an HTTPS POST request that triggers a "Provisioning" function. This function generates a signed JSON Web Token (JWT) with an expiration claim (exp), stores the grant in a NoSQL database (e.g., DynamoDB), and triggers a "Notification" function. The Notification function dispatches the communication (SMS, email) containing a URL. This URL points to a static web page that includes the JWT and a link to a Progressive Web App (PWA) client, which uses the JWT to authenticate with the POC backend. Revocation is handled by a time-to-live (TTL) attribute on the database record, which triggers a "Revocation" function upon expiry to invalidate the JWT or remove the user from the talkgroup's Access Control List (ACL).

• Mermaid Diagram:

  sequenceDiagram
      participant Sub_Device as Subscriber Device
      participant APIGW as API Gateway
      participant Prov_Func as Provisioning Lambda
      participant Notif_Func as Notification Lambda
      participant DB as DynamoDB
      participant NonSub_Device as Non-Subscriber Device
  
      Sub_Device->>APIGW: POST /invite {contact_info}
      APIGW->>Prov_Func: Trigger event
      Prov_Func->>DB: Write grant with TTL
      Prov_Func->>Notif_Func: Invoke with contact_info & signed_url
      Notif_Func->>NonSub_Device: Send SMS with link
      NonSub_Device->>APIGW: GET /join_session
      APIGW-->>NonSub_Device: Return PWA with embedded JWT
      Note right of DB: TTL expires on grant record
      DB->>APIGW: Trigger /revoke endpoint
      APIGW-->>Prov_Func: Invalidate JWT / remove from ACL
  

1.2. WebRTC-Based Thin Client

• Enabling Description: This variation eliminates the need for a downloadable native application. The control device, upon granting access, transmits a URL to the non-subscriber. This URL opens a web application in a standard mobile or desktop browser. The application utilizes WebRTC (Web Real-Time Communication) APIs for all media (audio/video) and data channel communication. The control device acts as a signaling server (e.g., using WebSockets) to manage session establishment and a STUN/TURN server to facilitate NAT traversal. The "talkgroup" is a WebRTC mesh or MCU-based conference room. Access is controlled by a time-limited authentication token passed in the URL, which the signaling server validates. Revocation occurs when the token expires or is invalidated by the server.

• Mermaid Diagram:

  flowchart TD
      A[Subscriber Device] -- 1. Request Invite --> B{Control Device / Signaling Server};
      B -- 2. Send Unique URL --> C[Non-Subscriber Device];
      C -- 3. Opens URL in Browser --> D[Web App Client];
      D -- 4. WebSocket Handshake w/ Token --> B;
      B -- 5. STUN/TURN Config --> D;
      D -- 6. Establish Peer Connection --> E[Other Talkgroup Members];
      B -- 7. Token Expires --> F[Session Terminated];
  

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Derivative Set 2: Operational Parameter Expansion

2.1. Massive-Scale Flash Event Provisioning

• Enabling Description: For events with 100,000+ temporary users (e.g., city marathons, protests), the system is designed for massive ingress. Instead of individual invitations, the subscriber (event organizer) pre-registers a block of phone numbers or email domains. The control device, built on a distributed hash table (DHT) and content delivery network (CDN), pre-generates cryptographically secure access tokens. The "invitation" is a generic URL or QR code distributed publicly. Upon access, a user's device hashes its device ID (e.g., IMEI) and sends it to a load-balanced endpoint. The endpoint uses the DHT to locate the relevant shard of the access database and validates the device against the pre-registered list, issuing a short-lived token. The POC application is hosted on a CDN to handle the download burst. The talkgroup itself is a broadcast-only channel with an optional, heavily moderated listen-and-reply queue to prevent chaos.

• Mermaid Diagram:

  graph TD
      subgraph Pre-Event Setup
          A[Organizer Device] --> B{Control Plane};
          B --> C[Register Phone # Blocks];
          B --> D[Pre-generate Tokens];
          B --> E[Distribute Public URL/QR Code];
      end
      subgraph Event Ingress
          F[Non-Subscriber Scans QR] --> G{Landing Page on CDN};
          G --> H[Device ID Hashing];
          H --> I[Load Balancer];
          I --> J[DHT Shard 1];
          I --> K[DHT Shard 2];
          I --> L[DHT Shard N];
          J --> M{Validate & Issue Token};
          M --> N[Connect to Broadcast Talkgroup];
      end
  

2.2. Disconnected, Intermittent, and Low-Bandwidth (DIL) Operations

• Enabling Description: This variation is designed for disaster recovery or battlefield scenarios with no reliable backhaul. The subscriber's device generates a signed "invitation packet" that contains the talkgroup configuration, an ACL, a public key, and an expiration timestamp. This packet can be transferred to a non-subscriber's device via local, out-of-band means like Bluetooth, Wi-Fi Direct, or a physical data transfer device (e.g., USB drive). The "POC application" is also transferred this way. The application, upon installation, validates the signature of the invitation packet. Communication within the talkgroup operates on a local mesh network, using a delay-tolerant networking (DTN) protocol. Messages are stored and forwarded as devices move in and out of range. Access automatically expires when the timestamp in the packet is reached.

• Mermaid Diagram:

  stateDiagram-v2
      [*] --> Unprovisioned
      Unprovisioned --> Provisioned: Receive Signed Packet (OOB)
      Provisioned: Client validates signature & timestamp
      Provisioned --> Active: Join local mesh network
      Active --> Active: Store & Forward PTT data
      Active --> Expired: Timestamp reached
      Provisioned --> Expired: Timestamp reached
      Expired --> [*]
  

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Derivative Set 3: Cross-Domain Applications

3.1. Aerospace: Temporary Avionics Data-Link Access

• Enabling Description: A flight operations manager (subscriber) grants a third-party ground maintenance crew (non-subscriber) temporary access to an aircraft's secure ACARS or FMS data stream for a specific tail number. The manager uses a flight ops terminal to enter the maintenance team leader's corporate email. The control device sends an email with a link to a sandboxed, web-based diagnostic client. This client establishes a secure, temporary VPN tunnel to a specific data bus on the aircraft via the airport's ground network. Access is limited to read-only telemetry and expires after a 2-hour window or when the aircraft's "Weight on Wheels" sensor indicates takeoff.

• Mermaid Diagram:

  flowchart LR
      subgraph On-Ground Ops
          A[Flight Ops Manager] -- 1. Invite via Email --> B{Control Device};
          B -- 2. Send Link --> C[Maint. Crew Laptop];
          C -- 3. Click Link --> D{Web-based Diagnostic Client};
          D -- 4. Auth & Tunnel Request --> B;
          B -- 5. Provision VPN --> E[Aircraft Data Gateway];
          D -- 6. Secure Telemetry Stream --> E;
      end
      F[Aircraft WoW Sensor] -- 7. Takeoff Signal --> E;
      E -- 8. Terminate VPN --> B;
  

3.2. AgTech: Ad-Hoc IoT Farm Sensor Network

• Enabling Description: A farm owner (subscriber) needs to grant a crop consultant (non-subscriber) temporary access to a section of their field's IoT network (soil moisture sensors, drone camera feeds). The owner uses a farm management app to draw a geofence on a map and selects the consultant from their contacts. The control device sends an SMS with a link to the consultant. The link opens a specialized app that displays data only from sensors within that geofence. The "talkgroup" is a data channel for controlling irrigation valves or tasking a drone for that specific zone. Access is automatically revoked after 24 hours or if the consultant's device GPS reports they are outside the geofence for more than 15 minutes.

• Mermaid Diagram:

  sequenceDiagram
      actor Owner
      participant App as Farm Mgmt App
      participant Server as Control Device
      actor Consultant
  
      Owner->>App: Define Geofence, Select Consultant
      App->>Server: Transmit Invite Request
      Server->>Consultant: Send SMS with Link
      Consultant->>Server: Access Link, Provide Location
      alt GPS inside Geofence
          Server->>Consultant: Stream Sensor/Drone Data
      else GPS outside Geofence
          Server->>Consultant: Deny Access
      end
      Note over Server, Consultant: Access revoked after 24hr or on leaving geofence.
  

3.3. Smart Home: Guest Access Control

• Enabling Description: A homeowner grants a house sitter temporary access to a subset of smart home devices (e.g., front door lock, specific cameras, thermostat). The homeowner uses their primary smart home app to select the "Guest Access" function, enters the sitter's phone number, and checks which devices to share. The system sends a link that prompts the sitter to download a lightweight "Guest" version of the app. Upon first open, the app uses the phone's secure element to generate a temporary cryptographic key pair and registers the public key with the home hub. All commands are signed by this temporary key. The homeowner can revoke access instantly, or it can be programmed to expire at a set date and time.

• Mermaid Diagram:

  classDiagram
      class HomeHub {
          -masterKey
          +deviceList
          +grantAccess(contact, deviceACL, duration)
          +revokeAccess(guestID)
      }
      class HomeownerApp {
          +requestGuestAccess()
      }
      class GuestApp {
          -guestPrivateKey
          +authenticateWithHub()
          +controlDevice(deviceID)
      }
      HomeownerApp --|> HomeHub : controls
      GuestApp --|> HomeHub : temporary control
  

---

Derivative Set 4: Integration with Emerging Technologies

4.1. AI-Driven Predictive Provisioning

• Enabling Description: In a public safety context, the control device integrates with a CAD (Computer-Aided Dispatch) system and an AI/ML model. When a multi-agency incident is dispatched (e.g., a 5-alarm fire), the AI model analyzes the incident type, location, and units dispatched. It predictively identifies likely non-subscriber participants (e.g., hospital ER supervisors, public utility foremen, nearby school principals) based on historical incident data and GIS information. The system automatically sends provisional access links to these individuals, who can then choose to join the incident talkgroup. The AI also monitors talkgroup sentiment and keyword mentions to suggest inviting additional experts if the situation evolves.

• Mermaid Diagram:

  graph TD
      A[CAD System] -- 1. Dispatch Event --> B(AI/ML Model);
      B -- 2. Analyze Incident --> C{Predict Participants};
      C -- 3. Generate Invite List --> D[Control Device];
      D -- 4. Send Provisional Links --> E[Hospital ER];
      D --> F[Utility Foreman];
      D --> G[School Principal];
      H[Incident Talkgroup] -- 5. Audio Stream --> B;
      B -- 6. Real-time Analysis --> I{Suggest New Experts};
      I --> D;
  

4.2. Blockchain/NFT-Based Access Tokens

• Enabling Description: The access grant is tokenized as a non-fungible token (NFT) on a private, permissioned blockchain. When a subscriber invites a non-subscriber, the control device (acting as a minting service) creates a new NFT. The NFT's metadata contains the talkgroup ID, the grantee's identifier (e.g., a hashed phone number), and an "expiration" property. The invitation link allows the non-subscriber to claim the NFT into a temporary, in-app crypto wallet. The POC application authenticates to the talkgroup by presenting this NFT and signing a challenge with the wallet's private key. The smart contract governing the NFT automatically renders it invalid after the expiration time, providing a decentralized and auditable method of revoking access.

• Mermaid Diagram:

  sequenceDiagram
      participant Sub as Subscriber
      participant Ctrl as Control Device
      participant Chain as Blockchain
      participant NonSub as Non-Subscriber
  
      Sub->>Ctrl: Request Invite
      Ctrl->>Chain: Deploy AccessToken Smart Contract (NFT)
      Chain-->>Ctrl: Contract Address
      Ctrl->>NonSub: Send Link to Claim NFT
      NonSub->>Chain: Claim NFT to In-App Wallet
      NonSub->>Ctrl: Request PTT Session w/ NFT Proof
      Ctrl->>Chain: Verify NFT Ownership & Validity
      Chain-->>Ctrl: Verification Result
      Ctrl->>NonSub: Grant PTT Access
  

---

Derivative Set 5: Inverse and Safe Failure Modes

5.1. Graceful Degradation to Low-Fidelity Mode

• Enabling Description: The downloaded POC application continuously monitors the non-subscriber device's state (battery level, network signal strength, CPU load). If any parameter crosses a critical low threshold, the application automatically switches to a "low-fidelity" mode. In this mode, video transmission is disabled, audio is transcoded to a low-bitrate codec (e.g., Opus at 8kbps), non-essential UI elements are hidden, and background data synchronization is paused. The device sends a status flag to the control server, which then signals other participants that the user is in a degraded state. This ensures core PTT voice functionality is maintained in adverse conditions.

• Mermaid Diagram:

  stateDiagram-v2
      state "High Fidelity" as HiFi
      state "Low Fidelity" as LoFi
  
      [*] --> HiFi
      HiFi --> LoFi: Battery < 15% OR Signal < -110dBm
      LoFi --> HiFi: Battery > 20% AND Signal > -100dBm
      HiFi: Full UI, HD Audio, Video Enabled
      LoFi: Minimal UI, Low-bitrate Codec, Video Disabled
  

---

Combination Prior Art Scenarios with Open-Source Standards

1. Combination with Matrix/Element: A "control device" is implemented as a Matrix Synapse homeserver with a custom provisioning module. A public safety agency runs this server. An administrator, using a modified Element client, invites a non-subscriber by their phone number. The provisioning module uses a service like Twilio to send an SMS with a matrix.to invitation link. The link directs the user to a lightweight web-based Element client, which generates an ephemeral guest account on the homeserver and automatically joins the specified encrypted room (the "talkgroup"). The guest account is automatically deactivated by a cron job on the server after the pre-determined time has elapsed.

2. Combination with FIDO2/WebAuthn: The system forgoes passwords or traditional tokens for non-subscribers. The invitation link leads to a registration page. The page invokes the browser's WebAuthn API, prompting the user to authenticate with their device's built-in biometrics (e.g., fingerprint, Face ID). This creates a public-key credential which is stored by the control device. To join the POC talkgroup, the application (native or web-based) issues a cryptographic challenge which must be signed by the user's private key, again via a biometric prompt. This provides secure, passwordless, and temporary access tied to the user's specific device. Access is revoked by simply deleting the stored public key from the control device's database.

3. Combination with Open Policy Agent (OPA): Access control logic for the POC talkgroups is decoupled from the control device and managed by the Open Policy Agent (OPA) open-source engine. When a non-subscriber attempts to join, the control device queries the OPA service with a JSON object containing user attributes (e.g., user_id, contact_info, requested_talkgroup, current_time). OPA evaluates these attributes against a set of policies written in the Rego language. The policy can enforce complex rules, such as "Allow access only if the request is within the time window specified in the invitation AND the user is not on a global blocklist." This allows for highly flexible and auditable access control that can be updated without redeploying the main control device application.