private void startController(final DiscoveryPeer localNode) {
    final PeerDiscoveryController controller = createController(localNode);
    this.controller = Optional.of(controller);
    controller.start();
  }
The peer discovery agent is the network component that sends and receives peer discovery messages
via UDP.
ethereum/p2p/src/main/java/org/hyperledger/besu/ethereum/p2p/discovery/PeerDiscoveryAgent.java