diff --git a/sec-beidou-rtcm/src/main/java/com/imdroid/sideslope/rtkcluster/RtkClusterService.java b/sec-beidou-rtcm/src/main/java/com/imdroid/sideslope/rtkcluster/RtkClusterService.java
index 4212808c..1361042f 100644
--- a/sec-beidou-rtcm/src/main/java/com/imdroid/sideslope/rtkcluster/RtkClusterService.java
+++ b/sec-beidou-rtcm/src/main/java/com/imdroid/sideslope/rtkcluster/RtkClusterService.java
@@ -19,6 +19,7 @@ import java.io.*;
 import java.net.InetSocketAddress;
 import java.net.ServerSocket;
 import java.net.Socket;
+import java.net.SocketTimeoutException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
 import java.time.LocalDateTime;
@@ -223,34 +224,55 @@ public class RtkClusterService implements ApplicationRunner {
 
         private void classifyConnection(Socket s) {
             exec.submit(() -> {
+                boolean assigned = false;
                 try {
-                    // short probe to classify role (increase to 1000ms to reduce misclassification)
-                    s.setSoTimeout(1000);
+                    s.setTcpNoDelay(true);
+                    s.setKeepAlive(true);
+                    s.setSoTimeout(1500);
                     InputStream in = s.getInputStream();
                     byte[] probe = new byte[256];
-                    int n = 0;
-                    try { n = in.read(probe); } catch (IOException ignore) {}
-                    // restore to blocking mode for steady-state
-                    s.setSoTimeout(0);
+                    int n;
+                    try {
+                        n = in.read(probe);
+                    } catch (SocketTimeoutException timeout) {
+                        n = 0; // treat as no immediate data
+                    } catch (IOException readError) {
+                        LOGGER.debug("Endpoint {} initial read failed: {}", port, readError.getMessage());
+                        closeQuietly(s);
+                        return;
+                    } finally {
+                        s.setSoTimeout(0);
+                    }
+
+                    if (n < 0) {
+                        LOGGER.debug("Endpoint {} connection closed during probe", port);
+                        return;
+                    }
+
                     if (n > 0 && isLikelyText(probe, n)) {
-                        // OUT connection (NMEA etc.)
-                        closeQuietly(outConn);
-                        s.setTcpNoDelay(true);
-                        s.setKeepAlive(true);
-                        outConn = s;
-                        LOGGER.debug("Endpoint {} OUT connected", port);
-                        pumpOut(outConn, probe, n);
+                        if (!isSocketAlive(outConn)) {
+                            outConn = s;
+                            assigned = true;
+                            LOGGER.debug("Endpoint {} OUT connected", port);
+                            pumpOut(s, probe, n);
+                        } else {
+                            LOGGER.info("Endpoint {} additional OUT connection detected; keeping existing", port);
+                        }
                     } else {
-                        // IN connection (RTCM sink)
-                        closeQuietly(inConn);
-                        s.setTcpNoDelay(true);
-                        s.setKeepAlive(true);
-                        inConn = s;
-                        LOGGER.debug("Endpoint {} IN connected", port);
+                        if (!isSocketAlive(inConn)) {
+                            inConn = s;
+                            assigned = true;
+                            LOGGER.debug("Endpoint {} IN connected", port);
+                        } else {
+                            LOGGER.info("Endpoint {} additional IN connection detected; keeping existing", port);
+                        }
                     }
                 } catch (IOException e) {
                     LOGGER.warn("classifyConnection error: {}", e.getMessage());
-                    closeQuietly(s);
+                } finally {
+                    if (!assigned) {
+                        closeQuietly(s);
+                    }
                 }
             });
         }
@@ -292,8 +314,7 @@ public class RtkClusterService implements ApplicationRunner {
             while (true) {
                 try {
                     Socket sink = inConn;
-                    if (sink == null || sink.isClosed()) {
-                        // avoid consuming queue when no sink, preventing starvation
+                    if (!isSocketAlive(sink)) {
                         Thread.sleep(20);
                         continue;
                     }
@@ -303,7 +324,12 @@ public class RtkClusterService implements ApplicationRunner {
                         os.write(data);
                         os.flush();
                     } catch (IOException e) {
-                        LOGGER.warn("Write RTCM failed on {}: {}", port, e.getMessage());
+                        String msg = e.getMessage();
+                        if (msg != null && msg.toLowerCase().contains("closed")) {
+                            LOGGER.debug("Write RTCM failed on {}: {}", port, msg);
+                        } else {
+                            LOGGER.warn("Write RTCM failed on {}: {}", port, msg);
+                        }
                         closeQuietly(sink);
                         inConn = null;
                     }
@@ -314,6 +340,10 @@ public class RtkClusterService implements ApplicationRunner {
             }
         }
 
+        private boolean isSocketAlive(Socket s) {
+            return s != null && s.isConnected() && !s.isClosed() && !s.isInputShutdown() && !s.isOutputShutdown();
+        }
+
         private void closeQuietly(Socket s) {
             if (s == null) return;
             try { s.close(); } catch (IOException ignore) {}