diff --git a/linux_chat.c b/linux_chat.c
index c571732..d063c52 100644
--- a/linux_chat.c
+++ b/linux_chat.c
@@ -10,7 +10,7 @@
 
 #define LOCAL_PORT 9000
 #define PEER_PORT  9001
-#define TIMEOUT_MS 500
+#define TIMEOUT_MS 200
 
 int main(int argc, char *argv[]) {
     if (argc != 2) {
@@ -19,16 +19,11 @@ int main(int argc, char *argv[]) {
     }
 
     int sock = socket(AF_INET6, SOCK_DGRAM, 0);
-    if (sock < 0) {
-        perror("socket");
-        return 1;
-    }
 
     struct sockaddr_in6 local = {0};
     local.sin6_family = AF_INET6;
     local.sin6_port = htons(LOCAL_PORT);
     local.sin6_addr = in6addr_any;
-
     bind(sock, (struct sockaddr*)&local, sizeof(local));
 
     struct sockaddr_in6 peer = {0};
@@ -36,46 +31,64 @@ int main(int argc, char *argv[]) {
     peer.sin6_port = htons(PEER_PORT);
     inet_pton(AF_INET6, argv[1], &peer.sin6_addr);
 
-    struct timeval tv;
-    tv.tv_sec = 0;
-    tv.tv_usec = TIMEOUT_MS * 1000;
+    struct timeval tv = {0, TIMEOUT_MS * 1000};
     setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
 
-    uint8_t seq = 0;
-    char input[DATA_LEN];
+    uint8_t send_seq = 0;
+    uint8_t waiting_ack = 0;
+    packet_t last_pkt;
 
     while (1) {
-        printf("You: ");
-        fflush(stdout);
-        fgets(input, sizeof(input), stdin);
+        /*  尝试接收 */
+        packet_t pkt;
+        struct sockaddr_in6 from;
+        socklen_t fromlen = sizeof(from);
 
-        packet_t pkt = {0};
-        pkt.type = TYPE_DATA;
-        pkt.seq = seq;
-        pkt.length = strlen(input);
-        memcpy(pkt.data, input, pkt.length);
+        int n = recvfrom(sock, &pkt, sizeof(pkt), 0,
+                         (struct sockaddr*)&from, &fromlen);
 
-        while (1) {
-            sendto(sock, &pkt, sizeof(pkt), 0,
-                   (struct sockaddr*)&peer, sizeof(peer));
+        if (n > 0) {
+            if (pkt.type == TYPE_DATA) {
+                printf("\nPeer: %s", pkt.data);
 
-            packet_t ack;
-            struct sockaddr_in6 from;
-            socklen_t fromlen = sizeof(from);
+                packet_t ack = {0};
+                ack.type = TYPE_ACK;
+                ack.seq = pkt.seq;
 
-            int n = recvfrom(sock, &ack, sizeof(ack), 0,
-                             (struct sockaddr*)&from, &fromlen);
-
-            if (n > 0 && ack.type == TYPE_ACK && ack.seq == seq) {
-                break;
+                sendto(sock, &ack, sizeof(ack), 0,
+                       (struct sockaddr*)&peer, sizeof(peer));
+            }
+            else if (pkt.type == TYPE_ACK &&
+                     waiting_ack && pkt.seq == send_seq) {
+                waiting_ack = 0;
+                send_seq ^= 1;
             }
-
-            usleep(TIMEOUT_MS * 1000);
         }
 
-        seq ^= 1;
-    }
+        /*  如果不在等 ACK，则允许发送 */
+        if (!waiting_ack) {
+            char buf[DATA_LEN];
+            printf("You: ");
+            fflush(stdout);
 
-    close(sock);
-    return 0;
+            if (fgets(buf, sizeof(buf), stdin) == NULL)
+                continue;
+
+            memset(&last_pkt, 0, sizeof(last_pkt));
+            last_pkt.type = TYPE_DATA;
+            last_pkt.seq = send_seq;
+            last_pkt.length = strlen(buf);
+            memcpy(last_pkt.data, buf, last_pkt.length);
+
+            sendto(sock, &last_pkt, sizeof(last_pkt), 0,
+                   (struct sockaddr*)&peer, sizeof(peer));
+
+            waiting_ack = 1;
+        } else {
+            /*  超时重传 */
+            sendto(sock, &last_pkt, sizeof(last_pkt), 0,
+                   (struct sockaddr*)&peer, sizeof(peer));
+            usleep(TIMEOUT_MS * 1000);
+        }
+    }
 }