# How Self-Healing Data Loops Automatically Elect a New Master Controller > A communication system where multiple nodes in a loop can automatically take over as the master controller if the current one fails, ensuring the network stays synchronized. - **Patent:** US 4677614 - **Original title:** Data communication system and method and communication controller and method therefor, having a data/clock synchronizer and method - **Owner:** Process Systems Inc - **Granted:** 1987 - **Status:** Public domain (expired) - **Times cited:** 83 - **Field:** telecommunications, mechanical, semiconductors ## What it does This patent describes a network of devices connected in a loop where every device is capable of acting as either a 'master' or a 'slave'. The master node provides the master clock, which keeps all other nodes (slaves) synchronized so they can pass data reliably. If the master node fails or is removed, the other nodes detect the silence and use a timing mechanism to decide which one will become the new master. This allows the network to stay operational without manual intervention, effectively creating a self-healing communication loop. ## What it does NOT cover - Does not cover networks that rely on a central server that cannot be replaced by a node. - Does not cover non-synchronous communication systems that do not use a master clock. - Does not cover systems where the master node is fixed and cannot be reassigned to another node. ## The clever bit The system assigns each node a different 'waiting time' after a failure is detected before it attempts to become the master, preventing multiple nodes from trying to take control at the exact same time. ## Real-world examples 1. Token ring network architectures 2. Industrial fieldbus communication systems 3. Redundant serial data loops in factory automation ## Why it matters This technology was a foundational step in building resilient industrial control systems and local area networks. By allowing nodes to self-elect a master, it eliminated the single point of failure that plagued early serial communication loops, making systems more reliable for factory automation and data transmission. ## Frequently asked questions ### What does How Self-Healing Data Loops Automatically Elect a New Master Controller cover? A communication system where multiple nodes in a loop can automatically take over as the master controller if the current one fails, ensuring the network stays synchronized. ### Who owns patent US 4677614? Process Systems Inc owns this patent, granted in 1987. ### 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 4677614 cited by? This patent has been cited by 83 later patents that build on its ideas. ### What problem does this patent solve? This technology was a foundational step in building resilient industrial control systems and local area networks. By allowing nodes to self-elect a master, it eliminated the single point of failure that plagued early serial communication loops, making systems more reliable for factory automation and data transmission. ### What does this patent NOT cover? Does not cover networks that rely on a central server that cannot be replaced by a node. **Full plain-English explainer:** https://patentbrief.org/patent/us/4677614/data-communication-system-and-method-and-communication-controller-and-method-therefor-having-a-dataclock-synchronizer-and-method **Original patent:** https://patents.google.com/patent/US4677614 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How Multiple Computers Share a Network Cable Without Crashing](https://patentbrief.org/patent/us/4063220/ethernet-packet-network) — This patent describes how multiple computers can share a single communication cable by listening for other transmissions and stopping their own if a collision occurs, then trying again later. - [How Cable Modems Fix Signal Distortions Before Sending Data](https://patentbrief.org/patent/us/6665308/apparatus-and-method-for-equalization-in-distributed-digital-data-transmission-systems) — A method for cable modems to pre-filter data so it arrives clearly at the central office, preventing signal errors caused by the messy physical wires between them. - [How Modems Use Guard Time to Switch Between Data and Commands](https://patentbrief.org/patent/us/4549302/hayes-modem-escape-sequence) — This patent describes a method for modems to safely switch from sending data to accepting commands without accidentally triggering that switch while transmitting normal files. - [How IBM's Storage Controllers Keep Data Backups in the Right Order](https://patentbrief.org/patent/us/5682513/cache-queue-entry-linking-for-dasd-record-updates) — A method for storage controllers to track and sequence data updates in a specific order, ensuring that remote backups remain consistent with the original data during a system failure. - [How to Send Data Streams Independently Without Connection Overload](https://patentbrief.org/patent/us/7904576/reliable-datagram-via-independent-source-destination-resources) — A method for sending multiple streams of data between devices using independent, reliable paths that keep data in the correct order without needing a constant connection.