diff --git a/common.h b/common.h
new file mode 100644
index 0000000..5c7eb17
--- /dev/null
+++ b/common.h
@@ -0,0 +1,22 @@
+#ifndef COMMON_H
+#define COMMON_H
+
+#include <stdint.h>
+
+#define TYPE_DATA 0
+#define TYPE_ACK  1
+
+#define PORT 9000
+#define BUF_SIZE 1024
+#define TIMEOUT_SEC 2
+
+/* 应用层协议数据包 */
+#pragma pack(push, 1)
+struct packet {
+    uint8_t seq;          // 停等协议序号：0 / 1
+    uint8_t type;         // 0=DATA, 1=ACK
+    char payload[BUF_SIZE - 2];
+};
+#pragma pack(pop)
+
+#endif