Implement sack based tcp loss recovery (RFC 6675)

[vpp.git] / src / vnet / tcp / tcp_newreno.c

diff --git a/src/vnet/tcp/tcp_newreno.c b/src/vnet/tcp/tcp_newreno.c
index 3525f4e..c66250e 100644 (file)
--- a/src/vnet/tcp/tcp_newreno.c
+++ b/src/vnet/tcp/tcp_newreno.c
@@ -51,9 +51,23 @@ newreno_rcv_cong_ack (tcp_connection_t * tc, tcp_cc_ack_t ack_type)
     }
   else if (ack_type == TCP_CC_PARTIALACK)
     {
-      tc->cwnd -= tc->bytes_acked;
-      if (tc->bytes_acked > tc->snd_mss)
-       tc->bytes_acked += tc->snd_mss;
+      /* RFC 6582 Sec. 3.2 */
+      if (!tcp_opts_sack_permitted (&tc->rcv_opts))
+       {
+         /* Deflate the congestion window by the amount of new data
+          * acknowledged by the Cumulative Acknowledgment field.
+          * If the partial ACK acknowledges at least one SMSS of new data,
+          * then add back SMSS bytes to the congestion window. This
+          * artificially inflates the congestion window in order to reflect
+          * the additional segment that has left the network. This "partial
+          * window deflation" attempts to ensure that, when fast recovery
+          * eventually ends, approximately ssthresh amount of data will be
+          * outstanding in the network.*/
+         tc->cwnd = (tc->cwnd > tc->bytes_acked) ?
+           tc->cwnd - tc->bytes_acked : 0;
+         if (tc->bytes_acked > tc->snd_mss)
+           tc->cwnd += tc->snd_mss;
+       }
     }
 }