From bf4269e98e0b9fa5ea4e835c99cac5cf6168f3dd Mon Sep 17 00:00:00 2001
From: Jeremy Lakeman <Jeremy.Lakeman@gmail.com>
Date: Thu, 29 Aug 2013 15:05:32 +0930
Subject: [PATCH] Adjust retransmission delay based on measured RTT

---
 overlay_packet.h |  4 ++--
 overlay_queue.c  | 49 +++++++++++++++++++++++++++++++++++++++---------
 route_link.c     |  1 +
 serval.h         |  4 ++++
 4 files changed, 47 insertions(+), 11 deletions(-)

diff --git a/overlay_packet.h b/overlay_packet.h
index 9188bd2d..aa105b25 100644
--- a/overlay_packet.h
+++ b/overlay_packet.h
@@ -31,8 +31,8 @@
 struct packet_destination{
   // if we've sent this packet once, what was the envelope sequence number?
   int sent_sequence;
-  // delay the next transmission. if we don't get an ack, send it again.
-  time_ms_t delay_until;
+  // track when we last sent this packet. if we don't get an ack, send it again.
+  time_ms_t transmit_time;
   // the actual out going stream for this packet
   struct network_destination *destination;
 };
diff --git a/overlay_queue.c b/overlay_queue.c
index 1d8fa97f..89faffcb 100644
--- a/overlay_queue.c
+++ b/overlay_queue.c
@@ -201,9 +201,10 @@ int overlay_payload_enqueue(struct overlay_frame *p)
       p->resend = 1;
   }
   
-  if (config.debug.verbose && config.debug.overlayframes){
-    int i=0;
-    for (i=0;i<p->destination_count;i++)
+  int i=0;
+  for (i=0;i<p->destination_count;i++){
+    p->destinations[i].sent_sequence=-1;
+    if (config.debug.verbose && config.debug.overlayframes)
       DEBUGF("Sending %s on interface %s", 
 	  p->destinations[i].destination->unicast?"unicast":"broadcast",
 	  p->destinations[i].destination->interface->name);
@@ -288,8 +289,11 @@ overlay_calc_queue_time(overlay_txqueue *queue, struct overlay_frame *frame){
     for(i=0;i<frame->destination_count;i++)
     {
       time_ms_t next_packet = limit_next_allowed(&frame->destinations[i].destination->transfer_limit);
-      if (next_packet < frame->destinations[i].delay_until)
-	next_packet = frame->destinations[i].delay_until;
+      if (frame->destinations[i].transmit_time){
+	time_ms_t delay_until = frame->destinations[i].transmit_time + frame->destinations[i].destination->resend_delay;
+	if (next_packet < delay_until)
+	  next_packet = delay_until;
+      }
       if (next_allowed_packet==0||next_packet < next_allowed_packet)
 	next_allowed_packet = next_packet;
     }
@@ -350,6 +354,15 @@ overlay_stuff_packet(struct outgoing_packet *packet, overlay_txqueue *queue, tim
     if (frame->destination_count==0 && frame->destination){
       link_add_destinations(frame);
       
+      int i=0;
+      for (i=0;i<frame->destination_count;i++){
+	frame->destinations[i].sent_sequence=-1;
+	if (config.debug.verbose && config.debug.overlayframes)
+	  DEBUGF("Sending %s on interface %s", 
+	      frame->destinations[i].destination->unicast?"unicast":"broadcast",
+	      frame->destinations[i].destination->interface->name);
+      }
+      
       // degrade packet version if required to reach the destination
       if (frame->packet_version > frame->next_hop->max_packet_version)
 	frame->packet_version = frame->next_hop->max_packet_version;
@@ -370,7 +383,8 @@ overlay_stuff_packet(struct outgoing_packet *packet, overlay_txqueue *queue, tim
 	  continue;
 	}
 	
-	if (frame->destinations[i].delay_until>now)
+	if (frame->destinations[i].transmit_time && 
+	  frame->destinations[i].transmit_time + frame->destinations[i].destination->resend_delay > now)
 	  continue;
 	
 	if (packet->buffer){
@@ -437,9 +451,13 @@ overlay_stuff_packet(struct outgoing_packet *packet, overlay_txqueue *queue, tim
       frame->delay_until = now + 5;
       goto skip;
     }
-
-    frame->destinations[destination_index].sent_sequence = frame->destinations[destination_index].destination->sequence_number;
-    frame->destinations[destination_index].delay_until = now+200;
+    
+    {
+      struct packet_destination *dest = &frame->destinations[destination_index];
+      dest->sent_sequence = dest->destination->sequence_number;
+      dest->transmit_time = now;
+    }
+    
     frame->transmit_count++;
     
     if (config.debug.overlayframes){
@@ -539,6 +557,19 @@ int overlay_queue_ack(struct subscriber *neighbour, struct network_destination *
 	  char acked = (seq_delta==0 || (seq_delta <= 32 && ack_mask&(1<<(seq_delta-1))))?1:0;
 
 	  if (acked){
+	    int rtt = now - frame->destinations[j].transmit_time;
+	    if (!destination->min_rtt || rtt < destination->min_rtt){
+	      destination->min_rtt = rtt;
+	      int delay = rtt * 2 + 40;
+	      if (delay < destination->resend_delay){
+		destination->resend_delay = delay;
+		if (config.debug.linkstate)
+		  DEBUGF("Adjusting resend delay to %d", destination->resend_delay);
+	      }
+	    }
+	    if (!destination->max_rtt || rtt > destination->max_rtt)
+	      destination->max_rtt = rtt;
+	    
 	    if (config.debug.overlayframes)
 	      DEBUGF("Packet %p to %s sent by seq %d, acked with seq %d", 
 		frame, alloca_tohex_sid(neighbour->sid), frame_seq, ack_seq);
diff --git a/route_link.c b/route_link.c
index f8587a38..2ac8e366 100644
--- a/route_link.c
+++ b/route_link.c
@@ -163,6 +163,7 @@ struct network_destination * new_destination(struct overlay_interface *interface
     ret->_ref_count=1;
     ret->encapsulation = encapsulation;
     ret->interface = interface;
+    ret->resend_delay = 1000;
 //    DEBUGF("Create ref %p, %d - %s", ret, ret->_ref_count, ret->interface->name);
   }
   return ret;
diff --git a/serval.h b/serval.h
index 5061a6c0..62e75590 100644
--- a/serval.h
+++ b/serval.h
@@ -403,6 +403,10 @@ struct network_destination {
 
   // time last packet was sent
   time_ms_t last_tx;
+  
+  int min_rtt;
+  int max_rtt;
+  int resend_delay;
 
   // sequence number of last packet sent to this destination.
   // Used to allow NACKs that can request retransmission of recent packets.