diff --git a/ClientTester/EchoClientTester/EchoDummyService/DummyClients.cs b/ClientTester/EchoClientTester/EchoDummyService/DummyClients.cs
index c956ee4..40ee3cc 100644
--- a/ClientTester/EchoClientTester/EchoDummyService/DummyClients.cs
+++ b/ClientTester/EchoClientTester/EchoDummyService/DummyClients.cs
@@ -1,3 +1,4 @@
+using System.Collections.Concurrent;
 using System.Diagnostics;
 using ClientTester.Packet;
 using LiteNetLib;
@@ -8,13 +9,14 @@ namespace ClientTester.EchoDummyService;
 
 public class DummyClients
 {
-    public NetManager manager;
-    public EventBasedNetListener listener;
+    private NetManager manager;
+    private EventBasedNetListener listener;
+    private NetDataWriter? writer;
     public NetPeer? peer;
     public int clientId;
 
     // seq → 송신 타임스탬프 (Stopwatch tick)
-    private readonly Dictionary<int, long> pendingPings = new();
+    private ConcurrentDictionary<int, long> pendingPings = new();
     private int seqNumber;
 
     // 통계
@@ -53,6 +55,7 @@ public class DummyClients
         this.clientId = clientId;
         listener = new EventBasedNetListener();
         manager = new NetManager(listener);
+        writer = new NetDataWriter();
 
         listener.PeerConnectedEvent += netPeer =>
         {
@@ -65,16 +68,16 @@ public class DummyClients
             short code = reader.GetShort();
             short bodyLength = reader.GetShort();
             string? msg = reader.GetString();
+            long sentTick;
 
             if (msg != null && msg.StartsWith("Echo seq:") &&
                 int.TryParse(msg.Substring("Echo seq:".Length), out int seq) &&
-                pendingPings.TryGetValue(seq, out long sentTick))
+                pendingPings.TryRemove(seq, out sentTick))
             {
                 double rttMs = (Stopwatch.GetTimestamp() - sentTick) * 1000.0 / Stopwatch.Frequency;
                 LastRttMs = rttMs;
                 TotalRttMs += rttMs;
                 RttCount++;
-                pendingPings.Remove(seq);
             }
 
             ReceivedCount++;
@@ -93,7 +96,7 @@ public class DummyClients
 
     public void SendPing()
     {
-        if (peer == null)
+        if (peer == null || writer == null)
         {
             return;
         }
@@ -101,15 +104,16 @@ public class DummyClients
         int seq = seqNumber++;
         pendingPings[seq] = Stopwatch.GetTimestamp();
 
-        NetDataWriter writer = new NetDataWriter();
         PacketHeader packetHeader = new PacketHeader();
         packetHeader.Code = 0;
         packetHeader.BodyLength = $"seq:{seq}".Length;
         writer.Put((short)packetHeader.Code);
         writer.Put((short)packetHeader.BodyLength);
         writer.Put($"Echo seq:{seq}");
-        peer.Send(writer, DeliveryMethod.ReliableOrdered);
+        // 순서보장 안함 HOL Blocking 제거
+        peer.Send(writer, DeliveryMethod.ReliableUnordered);
         SentCount++;
+        writer.Reset();
     }
 
     public double AvgRttMs => RttCount > 0 ? TotalRttMs / RttCount : 0.0;