diff --git a/hptp-send/src/main.rs b/hptp-send/src/main.rs
index e0ccfeb..1483ce5 100644
--- a/hptp-send/src/main.rs
+++ b/hptp-send/src/main.rs
@@ -235,16 +235,33 @@ where
     let mut sent: HashMap<SegIdx, Instant> = HashMap::new();
     let mut rtt_est: Duration = Duration::from_millis(1050);
     let mut drop_est: usize = 0;
+    let mut drop_est_made: bool = false;
 
     loop {
+        let now = Instant::now();
         log.debug_msg(format!("rtt_est is {}, drop_est is {}", rtt_est.as_millis(), drop_est)).await;
 
-        if drop_est > 50 {
-            in_flight = DEFAULT_IN_FLIGHT;
-        } else if drop_est > 35 {
-            in_flight = std::cmp::max(in_flight - 5, DEFAULT_IN_FLIGHT);
-        } else {
-            in_flight += 5;
+        if drop_est_made {
+            if drop_est > 50 {
+                in_flight = DEFAULT_IN_FLIGHT;
+            } else if drop_est > 35 {
+                in_flight = std::cmp::max(in_flight - 5, DEFAULT_IN_FLIGHT);
+            } else {
+                in_flight += 150;
+            }
+            drop_est_made = false;
+            let mut drain_idx = send_history.len();
+            for entry in send_history.iter().rev() {
+                if entry.1 >= now - (rtt_est / 2) {
+                    drain_idx -= 1;
+                } else {
+                    break;
+                }
+            }
+            send_history.drain(0..drain_idx);
+            ack_history.clear();
+            sent.clear();
+            acked.clear();
         }
 
         let timer = tokio::time::delay_until(deadline);
@@ -279,7 +296,6 @@ where
                 log.debug_msg(format!("got {} acks", idxs.len())).await;
                 src.ack(&idxs);
 
-                let now = Instant::now();
                 let mut rtts: Vec<Duration> = vec![];
 
                 for idx in idxs.iter().cloned() {
@@ -315,6 +331,7 @@ where
                 }
                 if total_pkts > 10 {
                     drop_est = 100 - (acked_pkts * 100 / total_pkts);
+                    drop_est_made = true;
                 }
             }
         };
@@ -322,7 +339,6 @@ where
         for m in to_send.drain(..) {
             match m {
                 UpMsg::Data{seg_idx, ..} => {
-                    let now = Instant::now();
                     send_history.push((seg_idx, now));
                     sent.insert(seg_idx, now);
                 },