diff --git a/src/BlockingRelayInterface.php b/src/BlockingRelayInterface.php
new file mode 100644
index 0000000..6e3088b
--- /dev/null
+++ b/src/BlockingRelayInterface.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Spiral\Goridge;
+
+/**
+ * Means that relay can't be used for non-blocking flow.
+ */
+interface BlockingRelayInterface extends RelayInterface
+{
+}
diff --git a/src/Frame.php b/src/Frame.php
index 61f8444..6ea657d 100644
--- a/src/Frame.php
+++ b/src/Frame.php
@@ -50,7 +50,9 @@ final class Frame
      * @var positive-int Flags for {@see $byte10}
      */
     public const BYTE10_STREAM = 0x01;
-    public const BYTE10_STOP = 0x02; // 2.9.0-alpha just streams
+    public const BYTE10_STOP = 0x02;
+    public const BYTE10_PING = 0x04;
+    public const BYTE10_PONG = 0x08;
 
     /**
      * @psalm-var FrameByte10Value
@@ -124,7 +126,7 @@ public static function packFrame(Frame $frame): string
      * @return HeaderList
      * @internal
      *
-     * @psalm-suppress InvalidReturnStatement, InvalidReturnType
+     * @psalm-suppress LessSpecificReturnStatement, MoreSpecificReturnType
      */
     public static function readHeader(string $header): array
     {
diff --git a/src/StreamRelay.php b/src/StreamRelay.php
index b47a996..acf2094 100644
--- a/src/StreamRelay.php
+++ b/src/StreamRelay.php
@@ -18,7 +18,7 @@
  * prefix:
  * [ flag       ][ message length, unsigned int 64bits, LittleEndian ]
  */
-class StreamRelay extends Relay
+class StreamRelay extends Relay implements BlockingRelayInterface
 {
     /**
      * @var resource