diff --git a/common.h b/common.h
index 5c7eb17..d9c6f58 100644
--- a/common.h
+++ b/common.h
@@ -3,20 +3,15 @@
 
 #include <stdint.h>
 
-#define TYPE_DATA 0
-#define TYPE_ACK  1
+#define DATA_LEN 512
+#define TYPE_DATA 1
+#define TYPE_ACK  2
 
-#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)
+typedef struct {
+    uint8_t type;      // DATA or ACK
+    uint8_t seq;       // 序号 0 / 1
+    uint16_t length;   // 数据长度
+    char data[DATA_LEN];
+} packet_t;
 
 #endif