A simple addition with significant performance implications:

sicslowpan tags TCP packets with the PACKETBUF_ATTR_PACKET_TYPE_STREAM
flag, which makes the underlying power-saving MAC layer keep the radio
on for some time after transmitting the packet. This allows reply
packets to be processed directly, significantly increasing TCP latency
and throughput.

core/net/mac/lpp.c

@@ -28,7 +28,7 @@
  *
  * This file is part of the Contiki operating system.
  *
- * $Id: lpp.c,v 1.26 2009/10/19 11:25:54 nifi Exp $
+ * $Id: lpp.c,v 1.27 2009/11/02 11:58:56 adamdunkels Exp $
  */
 
 /**
@@ -79,6 +79,7 @@
 #define WITH_ENCOUNTER_OPTIMIZATION   1
 #define WITH_ADAPTIVE_OFF_TIME        0
 #define WITH_PENDING_BROADCAST        1
+#define WITH_STREAMING                1
 
 #ifdef LPP_CONF_LISTEN_TIME
 #define LISTEN_TIME LPP_CONF_LISTEN_TIME
@@ -180,6 +181,13 @@ struct encounter {
 #define MAX_ENCOUNTERS 4
 LIST(encounter_list);
 MEMB(encounter_memb, struct encounter, MAX_ENCOUNTERS);
+
+#if WITH_STREAMING
+static uint8_t is_streaming;
+static struct ctimer stream_probe_timer, stream_off_timer;
+#define STREAM_PROBE_TIME CLOCK_SECOND / 128
+#define STREAM_OFF_TIME CLOCK_SECOND / 2
+#endif /* WITH_STREAMING */
 /*---------------------------------------------------------------------------*/
 static void
 turn_radio_on(void)
@@ -191,7 +199,7 @@ turn_radio_on(void)
 static void
 turn_radio_off(void)
 {
-  if(lpp_is_on) {
+  if(lpp_is_on && is_streaming == 0) {
     radio->off();
   }
   /*  leds_off(LEDS_YELLOW);*/
@@ -247,6 +255,12 @@ turn_radio_on_callback(void *packet)
   /*  printf("enc\n");*/
 }
 /*---------------------------------------------------------------------------*/
+static void
+stream_off(void *dummy)
+{
+  is_streaming = 0;
+}
+/*---------------------------------------------------------------------------*/
 /* This function goes through all encounters to see if it finds a
    matching neighbor. If so, we set a ctimer that will turn on the
    radio just before we expect the neighbor to send a probe packet. If
@@ -261,6 +275,18 @@ turn_radio_on_for_neighbor(rimeaddr_t *neighbor, struct queue_list_item *i)
 {
   struct encounter *e;
 
+#if WITH_STREAMING
+  if(packetbuf_attr(PACKETBUF_ATTR_PACKET_TYPE) ==
+     PACKETBUF_ATTR_PACKET_TYPE_STREAM) {
+    is_streaming = 1;
+    turn_radio_on();
+    list_add(queued_packets_list, i);
+    ctimer_set(&stream_off_timer, STREAM_OFF_TIME,
+	       stream_off, NULL);
+    return;
+  }
+#endif /* WITH_STREAMING */
+  
   if(rimeaddr_cmp(neighbor, &rimeaddr_null)) {
 #if ! WITH_PENDING_BROADCAST
     /* We have been asked to turn on the radio for a broadcast, so we
@@ -402,6 +428,19 @@ send_probe(void)
   compower_accumulate(&compower_idle_activity);
 }
 /*---------------------------------------------------------------------------*/
+static void
+send_stream_probe(void *dummy)
+{
+  /* Turn on the radio for sending a probe packet and 
+     anticipating a data packet from a neighbor. */
+  turn_radio_on();
+  
+  /* Send a probe packet. */
+  send_probe();
+
+  is_streaming = 1;
+}
+/*---------------------------------------------------------------------------*/
 static int
 num_packets_to_send(void)
 {
@@ -718,6 +757,13 @@ read_packet(void)
 	      /* Send a probe packet to catch any reply from the other node. */
 	      restart_dutycycle(PROBE_AFTER_TRANSMISSION_TIME);
 #endif /* WITH_PROBE_AFTER_TRANSMISSION */
+
+#if WITH_STREAMING
+	      if(is_streaming) {
+		ctimer_set(&stream_probe_timer, STREAM_PROBE_TIME,
+			   send_stream_probe, NULL);
+	      }
+#endif /* WITH_STREAMING */
 	    }
 
 #if WITH_ACK_OPTIMIZATION

core/net/mac/xmac.c

@@ -28,7 +28,7 @@
  *
  * This file is part of the Contiki operating system.
  *
- * $Id: xmac.c,v 1.39 2009/10/19 21:27:02 adamdunkels Exp $
+ * $Id: xmac.c,v 1.40 2009/11/02 11:58:56 adamdunkels Exp $
  */
 
 /**
@@ -54,6 +54,10 @@
 
 #include "contiki-conf.h"
 
+#ifdef EXPERIMENT_SETUP
+#include "experiment-setup.h"
+#endif
+
 #include <string.h>
 
 #define WITH_CHANNEL_CHECK           0    /* Seems to work badly when enabled */
@@ -160,12 +164,12 @@ static const struct radio_driver *radio;
 #define PRINTF(...) printf(__VA_ARGS__)
 #define PRINTDEBUG(...) printf(__VA_ARGS__)
 #else
-#undef LEDS_ON
+/*#undef LEDS_ON
 #undef LEDS_OFF
 #undef LEDS_TOGGLE
 #define LEDS_ON(x)
 #define LEDS_OFF(x)
-#define LEDS_TOGGLE(x)
+#define LEDS_TOGGLE(x)*/
 #define PRINTF(...)
 #define PRINTDEBUG(...)
 #endif
@@ -205,6 +209,11 @@ LIST(encounter_list);
 MEMB(encounter_memb, struct encounter, MAX_ENCOUNTERS);
 #endif /* WITH_ENCOUNTER_OPTIMIZATION */
 
+static uint8_t is_streaming;
+static rimeaddr_t is_streaming_to, is_streaming_to_too;
+static rtimer_clock_t stream_until;
+#define DEFAULT_STREAM_TIME (RTIMER_ARCH_SECOND)
+
 #ifndef MIN
 #define MIN(a, b) ((a) < (b)? (a) : (b))
 #endif /* MIN */
@@ -229,7 +238,8 @@ on(void)
 static void
 off(void)
 {
-  if(xmac_is_on && radio_is_on != 0 && is_listening == 0) {
+  if(xmac_is_on && radio_is_on != 0 && is_listening == 0 &&
+     is_streaming == 0) {
     radio_is_on = 0;
     radio->off();
     LEDS_OFF(LEDS_RED);
@@ -244,6 +254,14 @@ powercycle(struct rtimer *t, void *ptr)
   rtimer_clock_t should_be, adjust;
 #endif /* WITH_TIMESYNCH */
 
+  if(is_streaming) {
+    if(!RTIMER_CLOCK_LT(RTIMER_NOW(), stream_until)) {
+      is_streaming = 0;
+      rimeaddr_copy(&is_streaming_to, &rimeaddr_null);
+      rimeaddr_copy(&is_streaming_to_too, &rimeaddr_null);
+    }
+  }
+
 
   PT_BEGIN(&pt);
 
@@ -438,6 +456,8 @@ send_packet(void)
   int is_reliable;
   struct encounter *e;
   struct queuebuf *packet;
+  int is_already_streaming = 0;
+
 
 #if WITH_RANDOM_WAIT_BEFORE_SEND
   {
@@ -445,6 +465,7 @@ send_packet(void)
     while(RTIMER_CLOCK_LT(RTIMER_NOW(), t));
   }
 #endif /* WITH_RANDOM_WAIT_BEFORE_SEND */
+
   
   /* Create the X-MAC header for the data packet. */
   packetbuf_set_addr(PACKETBUF_ADDR_SENDER, &rimeaddr_node_addr);
@@ -473,8 +494,8 @@ send_packet(void)
   len = framer_get()->create();
   strobe_len = len + sizeof(struct xmac_hdr);
   if(len == 0 || strobe_len > sizeof(strobe)) {
-    /* Failed to send */
+    /* Failed to send */ 
-    PRINTF("xmac: send failed, too large header\n");
+   PRINTF("xmac: send failed, too large header\n");
     return 0;
   }
   memcpy(strobe, packetbuf_hdrptr(), len);
@@ -493,25 +514,48 @@ send_packet(void)
 
 #if WITH_CHANNEL_CHECK
   /* Check if there are other strobes in the air. */
-  waiting_for_packet = 1;
+  if(!someone_is_sending) {
-  on();
+    waiting_for_packet = 1;
-  t0 = RTIMER_NOW();
+    on();
-  while(RTIMER_CLOCK_LT(RTIMER_NOW(), t0 + xmac_config.strobe_wait_time * 2)) {
+    t0 = RTIMER_NOW();
-    len = radio->read(&strobe.hdr, sizeof(strobe.hdr));
+    while(RTIMER_CLOCK_LT(RTIMER_NOW(), t0 + xmac_config.strobe_wait_time * 2)) {
-    if(len > 0) {
+      len = radio->read(&strobe.hdr, sizeof(strobe.hdr));
-      someone_is_sending = 1;
+      if(len > 0) {
+	someone_is_sending = 1;
+      }
     }
+    waiting_for_packet = 0;
   }
-  waiting_for_packet = 0;
   
   while(someone_is_sending);
 
 #endif /* WITH_CHANNEL_CHECK */
-  
+
+
   /* By setting we_are_sending to one, we ensure that the rtimer
      powercycle interrupt do not interfere with us sending the packet. */
   we_are_sending = 1;
 
+#if WITH_STREAMING
+  if(is_streaming == 1 &&
+     (rimeaddr_cmp(packetbuf_addr(PACKETBUF_ADDR_RECEIVER),
+		   &is_streaming_to) ||
+      rimeaddr_cmp(packetbuf_addr(PACKETBUF_ADDR_RECEIVER),
+		   &is_streaming_to_too))) {
+    is_already_streaming = 1;
+  }
+  if(packetbuf_attr(PACKETBUF_ATTR_PACKET_TYPE) ==
+     PACKETBUF_ATTR_PACKET_TYPE_STREAM) {
+    is_streaming = 1;
+    if(rimeaddr_cmp(&is_streaming_to, &rimeaddr_null)) {
+      rimeaddr_copy(&is_streaming_to, packetbuf_addr(PACKETBUF_ADDR_RECEIVER));
+    } else if(!rimeaddr_cmp(&is_streaming_to, packetbuf_addr(PACKETBUF_ADDR_RECEIVER))) {
+      rimeaddr_copy(&is_streaming_to_too, packetbuf_addr(PACKETBUF_ADDR_RECEIVER));
+    }
+    stream_until = RTIMER_NOW() + DEFAULT_STREAM_TIME;
+  }
+#endif /* WITH_STREAMING */
+
   off();
 
 #if WITH_ENCOUNTER_OPTIMIZATION
@@ -539,7 +583,8 @@ send_packet(void)
 #if WITH_ACK_OPTIMIZATION
       /* Wait until the receiver is expected to be awake */
       if(packetbuf_attr(PACKETBUF_ATTR_PACKET_TYPE) !=
-	 PACKETBUF_ATTR_PACKET_TYPE_ACK) {
+	 PACKETBUF_ATTR_PACKET_TYPE_ACK &&
+	 is_streaming == 0) {
 	/* Do not wait if we are sending an ACK, because then the
 	   receiver will already be awake. */
 	while(RTIMER_CLOCK_LT(RTIMER_NOW(), expected));
@@ -564,6 +609,8 @@ send_packet(void)
     on();
   }
 
+  if(!is_already_streaming) {
+    
   watchdog_stop();
   got_strobe_ack = 0;
   for(strobes = 0;
@@ -624,37 +671,36 @@ send_packet(void)
       on();
       }*/
   }
+  }
 
+#if WITH_ACK_OPTIMIZATION
   /* If we have received the strobe ACK, and we are sending a packet
      that will need an upper layer ACK (as signified by the
      PACKETBUF_ATTR_RELIABLE packet attribute), we keep the radio on. */
   if(got_strobe_ack && (packetbuf_attr(PACKETBUF_ATTR_RELIABLE) ||
-			packetbuf_attr(PACKETBUF_ATTR_ERELIABLE))) {
+			packetbuf_attr(PACKETBUF_ATTR_ERELIABLE) ||
-
+			packetbuf_attr(PACKETBUF_ATTR_PACKET_TYPE) ==
-#if WITH_ACK_OPTIMIZATION
+			PACKETBUF_ATTR_PACKET_TYPE_STREAM)) {
     on(); /* Wait for ACK packet */
     waiting_for_packet = 1;
-#else /* WITH_ACK_OPTIMIZATION */
-    off();
-#endif /* WITH_ACK_OPTIMIZATION */
-
   } else {
-
+    off();
-    off(); /* shell ping don't seem to work with off() here, so we'll
-	     keep it on() for a while. */
   }
+#else /* WITH_ACK_OPTIMIZATION */
+  off();
+#endif /* WITH_ACK_OPTIMIZATION */
 
   /* restore the packet to send */
   queuebuf_to_packetbuf(packet);
   queuebuf_free(packet);
 
   /* Send the data packet. */
-  if(is_broadcast || got_strobe_ack) {
+  if(is_broadcast || got_strobe_ack || is_streaming) {
     radio->send(packetbuf_hdrptr(), packetbuf_totlen());
   }
 
 #if WITH_ENCOUNTER_OPTIMIZATION
-  if(got_strobe_ack) {
+  if(got_strobe_ack && !is_streaming) {
     register_encounter(packetbuf_addr(PACKETBUF_ADDR_RECEIVER), encounter_time);
   }
 #endif /* WITH_ENCOUNTER_OPTIMIZATION */
@@ -738,7 +784,6 @@ read_packet(void)
     hdr = packetbuf_dataptr();
 
     if(hdr->dispatch != DISPATCH) {
-      
       someone_is_sending = 0;
       if(rimeaddr_cmp(packetbuf_addr(PACKETBUF_ADDR_RECEIVER),
                                      &rimeaddr_node_addr) ||

core/net/rime/packetbuf.h

@@ -40,7 +40,7 @@
  *
  * This file is part of the Contiki operating system.
  *
- * $Id: packetbuf.h,v 1.3 2009/10/19 21:28:11 adamdunkels Exp $
+ * $Id: packetbuf.h,v 1.4 2009/11/02 11:58:56 adamdunkels Exp $
  */
 
 /**
@@ -316,6 +316,8 @@ extern const char *packetbuf_attr_strings[];
 
 #define PACKETBUF_ATTR_PACKET_TYPE_DATA 0
 #define PACKETBUF_ATTR_PACKET_TYPE_ACK 1
+#define PACKETBUF_ATTR_PACKET_TYPE_STREAM 2
+
 enum {
   PACKETBUF_ATTR_NONE,
   PACKETBUF_ATTR_CHANNEL,

core/net/sicslowpan.c

@@ -32,7 +32,7 @@
  *
  * This file is part of the Contiki operating system.
  *
- * $Id: sicslowpan.c,v 1.9 2009/09/18 16:37:17 nifi Exp $
+ * $Id: sicslowpan.c,v 1.10 2009/11/02 11:58:56 adamdunkels Exp $
  */
 /**
  * \file
@@ -1139,7 +1139,12 @@ output(uip_lladdr_t *localdest)
   /* reset rime buffer */
   packetbuf_clear();
   rime_ptr = packetbuf_dataptr();
-  
+
+  if(UIP_IP_BUF->proto == UIP_PROTO_TCP) {
+    packetbuf_set_attr(PACKETBUF_ATTR_PACKET_TYPE,
+		       PACKETBUF_ATTR_PACKET_TYPE_STREAM);
+  }
+    
   /*
    * The destination address will be tagged to each outbound
    * packet. If the argument localdest is NULL, we are sending a
@@ -1445,6 +1450,7 @@ input(const struct mac_driver *r)
     sicslowpan_len = 0;
     processed_ip_len = 0;
 #endif /* SICSLOWPAN_CONF_FRAG */
+
     tcpip_input();
 #if SICSLOWPAN_CONF_FRAG
   }