diff --git a/src/DiscoveredDeviceViewModel.cs b/src/DiscoveredDeviceViewModel.cs
index 7e787ad..926fec1 100644
--- a/src/DiscoveredDeviceViewModel.cs
+++ b/src/DiscoveredDeviceViewModel.cs
@@ -69,7 +69,7 @@ public partial class DiscoveredDeviceViewModel : ObservableObject, IDisposable
   /// <summary>
   /// Sets or returns the universal service name (USN) of the device.
   /// </summary>
-  public string Usn => _device.Usn;
+  public string? Usn => _device.Usn;
 
   /// <summary>
   /// Sets or returns a URL pointing to the device description document for this device.
@@ -138,7 +138,15 @@ public partial class DiscoveredDeviceViewModel : ObservableObject, IDisposable
 
   public override bool Equals(object? obj)
   {
-    return obj is DiscoveredDeviceViewModel viewModel && Equals(viewModel.Usn, Usn);
+    if (obj is not DiscoveredDeviceViewModel viewModel)
+      return false;
+    if (viewModel.Usn != null && !Equals(viewModel.Usn, Usn))
+      return false;
+    if (!Equals(viewModel.MacAddress, MacAddress))
+      return false;
+    if (!Equals(viewModel.IpAddress, IpAddress))
+      return false;
+    return true;
   }
 
   public void Dispose()
diff --git a/src/MainWindow.axaml b/src/MainWindow.axaml
index 3fd0694..9fcfa8a 100644
--- a/src/MainWindow.axaml
+++ b/src/MainWindow.axaml
@@ -29,6 +29,11 @@
                 <Button Command="{Binding SearchDevicesNowCommand}" Content="Search now" />
                 <Button Command="{Binding ResearchCommand}" Content="Search more" />
                 <Button Command="{Binding IpScanCommand}" Content="Scan ip" />
+                <TextBlock VerticalAlignment="Center">
+                    <Run Text="Found" />
+                    <Run Text="{Binding SddpDevices.Count}" />
+                    <Run Text="Items" />
+                </TextBlock>
             </StackPanel>
         </StackPanel>
         <Grid Grid.Column="1" Grid.Row="0">
@@ -64,6 +69,11 @@
                 <DataGridTextColumn Binding="{Binding MacAddress}" Header="Mac address" />
                 <DataGridTextColumn Binding="{Binding Version}" Header="Version" />
                 <DataGridTextColumn Binding="{Binding DiscoveredAt}" Header="Discovered at" />
+                <DataGridTemplateColumn Header="Presentation Page">
+                    <DataTemplate DataType="sddpViewer:DiscoveredDeviceViewModel">
+                        <HyperlinkButton Content="Open" NavigateUri="{Binding PresentationUrl}" ></HyperlinkButton>
+                    </DataTemplate>
+                </DataGridTemplateColumn>
             </DataGrid.Columns>
         </DataGrid>
     </Grid>
diff --git a/src/MainWindowViewModel.cs b/src/MainWindowViewModel.cs
index 058d4d6..6867848 100644
--- a/src/MainWindowViewModel.cs
+++ b/src/MainWindowViewModel.cs
@@ -24,25 +24,32 @@ public sealed partial class MainWindowViewModel : ObservableObject, IDisposable
 
   private static async void SddpDevices_OnCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
   {
-    switch (e.Action)
+    try
     {
-      case NotifyCollectionChangedAction.Add:
-        await AddAction(e.NewItems);
-        break;
-      case NotifyCollectionChangedAction.Remove:
-        RemoveAction(e.OldItems);
-        break;
-      case NotifyCollectionChangedAction.Replace:
-        RemoveAction(e.OldItems);
-        await AddAction(e.NewItems);
-        break;
-      case NotifyCollectionChangedAction.Reset:
-        RemoveAction(sender as ObservableCollection<DiscoveredDeviceViewModel>);
-        break;
-      case NotifyCollectionChangedAction.Move:
-        break;
-      default:
-        throw new ArgumentOutOfRangeException();
+      switch (e.Action)
+      {
+        case NotifyCollectionChangedAction.Add:
+          await AddAction(e.NewItems);
+          break;
+        case NotifyCollectionChangedAction.Remove:
+          RemoveAction(e.OldItems);
+          break;
+        case NotifyCollectionChangedAction.Replace:
+          RemoveAction(e.OldItems);
+          await AddAction(e.NewItems);
+          break;
+        case NotifyCollectionChangedAction.Reset:
+          RemoveAction(sender as ObservableCollection<DiscoveredDeviceViewModel>);
+          break;
+        case NotifyCollectionChangedAction.Move:
+          break;
+        default:
+          throw new ArgumentOutOfRangeException();
+      }
+    }
+    catch (Exception ex)
+    {
+      Console.WriteLine(ex.Message);
     }
   }
 
@@ -145,7 +152,7 @@ public sealed partial class MainWindowViewModel : ObservableObject, IDisposable
       var interNetwork = new IPAddress(ip);
       var cidr = $"{interNetwork}/{SelectedNetworkAdapter.PrefixLength}";
       var range = CidrHelper.GetIpRangeFromCidr(cidr);
-      var ipRange = IpRangeHelper.GetIPRange(range.Start, range.End).Where(IpAddressFilter);
+      var ipRange = IpRangeHelper.GetIPRange(range.Start, range.End).Where(address => IpAddressFilter(address, range));
       var collection = new ConcurrentBag<DiscoveredDeviceViewModel>();
       using var httpClient = new HttpClient();
       httpClient.Timeout = TimeSpan.FromSeconds(1);
@@ -158,7 +165,7 @@ public sealed partial class MainWindowViewModel : ObservableObject, IDisposable
           try
           {
             token.ThrowIfCancellationRequested();
-            DiscoveredSsdpDevice device = new DiscoveredSsdpDevice()
+            DiscoveredSsdpDevice device = new()
             {
               CacheLifetime = TimeSpan.Zero,
               DescriptionLocation = new Uri($"http://{address.ToString()}:8080/discovery/ssdp"),
@@ -177,19 +184,24 @@ public sealed partial class MainWindowViewModel : ObservableObject, IDisposable
         }
       );
 
-      foreach (DiscoveredDeviceViewModel viewModel in collection)
+      Dispatcher.UIThread.Invoke(() =>
       {
-        Dispatcher.UIThread.Invoke(() => SddpDevices.Add(viewModel));
-      }
+        foreach (DiscoveredDeviceViewModel viewModel in collection)
+        {
+          SddpDevices.Add(viewModel);
+        }
+      });
     }
   }
 
-  private bool IpAddressFilter(IPAddress arg)
+  private bool IpAddressFilter(IPAddress arg, (IPAddress Start, IPAddress End) range)
   {
-    if (this.SddpDevices.Any(x => Equals(x.IpAddress, arg)))
-    {
+    if (Equals(arg, range.Start))
+      return false;
+    if (Equals(arg, range.End))
+      return false;
+    if (this.SddpDevices.Any(x => Equals(x.IpAddress, arg)))
       return false;
-    }
     return true;
   }