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 1cd2594a..afcd96dc 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
@@ -204,17 +204,20 @@ public class RtkClusterService implements ApplicationRunner {
         private void classifyConnection(Socket s) {
             exec.submit(() -> {
                 try {
+                    // short probe to classify role
                     s.setSoTimeout(300);
                     InputStream in = s.getInputStream();
-                    byte[] probe = new byte[64];
+                    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);
                     if (n > 0 && isLikelyText(probe, n)) {
                         // OUT connection (NMEA etc.)
                         closeQuietly(outConn);
                         outConn = s;
                         LOGGER.info("Endpoint {} OUT connected", port);
-                        pumpOut(outConn);
+                        pumpOut(outConn, probe, n);
                     } else {
                         // IN connection (RTCM sink)
                         closeQuietly(inConn);
@@ -237,11 +240,16 @@ public class RtkClusterService implements ApplicationRunner {
             return printable >= Math.max(1, n - 4); // tolerate some non-printables
         }
 
-        private void pumpOut(Socket s) {
+        private void pumpOut(Socket s, byte[] firstBuf, int firstLen) {
             exec.submit(() -> {
                 try (InputStream in = s.getInputStream()) {
                     byte[] buf = new byte[2048];
                     int read;
+                    // deliver first classified bytes if any
+                    if (firstLen > 0) {
+                        String preview = new String(firstBuf, 0, Math.min(firstLen, 64), StandardCharsets.US_ASCII).replaceAll("\n", "\\n");
+                        LOGGER.info("[OUT:{}] {} bytes: {}...", port, firstLen, preview);
+                    }
                     while ((read = in.read(buf)) != -1) {
                         // For now, just log a short preview
                         String preview = new String(buf, 0, Math.min(read, 64), StandardCharsets.US_ASCII).replaceAll("\n", "\\n");