tcp: Make retransmission timeout (RTO) configurable

lwip-tcpip · May 9, 2022 · 239918c · 239918c
1 parent 876517e
commit 239918c
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Showing 2 changed files with 13 additions and 2 deletions.
diff --git a/src/core/tcp.c b/src/core/tcp.c
@@ -1901,8 +1901,10 @@ tcp_alloc(u8_t prio)
     /* As initial send MSS, we use TCP_MSS but limit it to 536.
        The send MSS is updated when an MSS option is received. */
     pcb->mss = INITIAL_MSS;
-    pcb->rto = 3000 / TCP_SLOW_INTERVAL;
-    pcb->sv = 3000 / TCP_SLOW_INTERVAL;
+    /* Set initial TCP's retransmission timeout to 3000 ms by default.
+       This value could be configured in lwipopts */
+    pcb->rto = LWIP_TCP_RTO_TIME / TCP_SLOW_INTERVAL;
+    pcb->sv = LWIP_TCP_RTO_TIME / TCP_SLOW_INTERVAL;
     pcb->rtime = -1;
     pcb->cwnd = 1;
     pcb->tmr = tcp_ticks;

diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
@@ -1337,6 +1337,15 @@
 #define TCP_CALCULATE_EFF_SEND_MSS      1
 #endif
 
+/**
+ * LWIP_TCP_RTO_TIME: Initial TCP retransmission timeout (ms).
+ * This defaults to 3 seconds as traditionally defined in the TCP protocol.
+ * For improving timely recovery on faster networks, this value could
+ * be lowered down to 1 second (RFC 6298)
+ */
+#if !defined LWIP_TCP_RTO_TIME || defined __DOXYGEN__
+#define LWIP_TCP_RTO_TIME               3000
+#endif
 
 /**
  * TCP_SND_BUF: TCP sender buffer space (bytes).