diff --git a/linux_chat.c b/linux_chat.c
index d063c52..f2b7bb1 100644
--- a/linux_chat.c
+++ b/linux_chat.c
@@ -1,94 +1,105 @@
 #include <stdio.h>
-#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <arpa/inet.h>
 #include <sys/socket.h>
-#include <sys/time.h>
+#include <sys/select.h>
 
 #include "common.h"
 
-#define LOCAL_PORT 9000
-#define PEER_PORT  9001
-#define TIMEOUT_MS 200
+/* 停等协议发送（带超时重传） */
+void send_with_stopwait(int sock,
+                        struct sockaddr_in6 *peer,
+                        struct packet *pkt)
+{
+    socklen_t len = sizeof(*peer);
 
-int main(int argc, char *argv[]) {
+    while (1) {
+        sendto(sock, pkt, sizeof(*pkt), 0,
+               (struct sockaddr *)peer, len);
+
+        fd_set fds;
+        FD_ZERO(&fds);
+        FD_SET(sock, &fds);
+
+        struct timeval tv;
+        tv.tv_sec = TIMEOUT_SEC;
+        tv.tv_usec = 0;
+
+        int ret = select(sock + 1, &fds, NULL, NULL, &tv);
+        if (ret > 0) {
+            struct packet ack;
+            recvfrom(sock, &ack, sizeof(ack), 0, NULL, NULL);
+            if (ack.type == TYPE_ACK && ack.seq == pkt->seq) {
+                return; // 正确 ACK
+            }
+        }
+        printf("[timeout] retransmit\n");
+    }
+}
+
+int main(int argc, char *argv[])
+{
     if (argc != 2) {
-        printf("Usage: %s <Windows IPv6>\n", argv[0]);
+        printf("用法: %s <对方IPv6地址>\n", argv[0]);
         return 1;
     }
 
     int sock = socket(AF_INET6, SOCK_DGRAM, 0);
 
-    struct sockaddr_in6 local = {0};
+    /* 绑定本地 IPv6 端口 */
+    struct sockaddr_in6 local;
+    memset(&local, 0, sizeof(local));
     local.sin6_family = AF_INET6;
-    local.sin6_port = htons(LOCAL_PORT);
     local.sin6_addr = in6addr_any;
-    bind(sock, (struct sockaddr*)&local, sizeof(local));
+    local.sin6_port = htons(PORT);
+    bind(sock, (struct sockaddr *)&local, sizeof(local));
 
-    struct sockaddr_in6 peer = {0};
+    /* 对端地址 */
+    struct sockaddr_in6 peer;
+    memset(&peer, 0, sizeof(peer));
     peer.sin6_family = AF_INET6;
-    peer.sin6_port = htons(PEER_PORT);
+    peer.sin6_port = htons(PORT);
     inet_pton(AF_INET6, argv[1], &peer.sin6_addr);
 
-    struct timeval tv = {0, TIMEOUT_MS * 1000};
-    setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
-
     uint8_t send_seq = 0;
-    uint8_t waiting_ack = 0;
-    packet_t last_pkt;
+    uint8_t recv_seq = 0;
+    struct packet pkt, rcv;
+
+    printf("Linux UDP IPv6 Stop-Wait Chat\n");
 
     while (1) {
-        /*  尝试接收 */
-        packet_t pkt;
-        struct sockaddr_in6 from;
-        socklen_t fromlen = sizeof(from);
+        /* 非阻塞接收 */
+        fd_set fds;
+        FD_ZERO(&fds);
+        FD_SET(sock, &fds);
+        struct timeval tv = {0, 100000};
 
-        int n = recvfrom(sock, &pkt, sizeof(pkt), 0,
-                         (struct sockaddr*)&from, &fromlen);
-
-        if (n > 0) {
-            if (pkt.type == TYPE_DATA) {
-                printf("\nPeer: %s", pkt.data);
-
-                packet_t ack = {0};
-                ack.type = TYPE_ACK;
-                ack.seq = pkt.seq;
-
-                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;
+        if (select(sock + 1, &fds, NULL, NULL, &tv) > 0) {
+            recvfrom(sock, &rcv, sizeof(rcv), 0, NULL, NULL);
+            if (rcv.type == TYPE_DATA) {
+                if (rcv.seq == recv_seq) {
+                    printf("\npeer: %s\n", rcv.payload);
+                    recv_seq ^= 1;
+                }
+                rcv.type = TYPE_ACK;
+                sendto(sock, &rcv, sizeof(rcv), 0,
+                       (struct sockaddr *)&peer, sizeof(peer));
             }
         }
 
-        /*  如果不在等 ACK，则允许发送 */
-        if (!waiting_ack) {
-            char buf[DATA_LEN];
-            printf("You: ");
-            fflush(stdout);
+        /* 发送 */
+        printf(">> ");
+        if (!fgets(pkt.payload, sizeof(pkt.payload), stdin))
+            break;
 
-            if (fgets(buf, sizeof(buf), stdin) == NULL)
-                continue;
+        pkt.seq = send_seq;
+        pkt.type = TYPE_DATA;
 
-            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);
-        }
+        send_with_stopwait(sock, &peer, &pkt);
+        send_seq ^= 1;
     }
+
+    close(sock);
+    return 0;
 }