forwardingenginep.nc

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/* $Id: ForwardingEngineP.nc,v 1.1.2.45 2006/06/26 22:55:33 scipio Exp $ */
/*
 * Copyright (c) 2006 Stanford University.
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 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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/**
 *  The ForwardingEngine is responsible for queueing and scheduling outgoing
 *  packets in a collection protocol. It maintains a pool of forwarding messages 
 *  and a packet send 
 *  queue. A ForwardingEngine with a forwarding message pool of size <i>F</i> 
 *  and <i>C</i> CollectionSenderC clients has a send queue of size
 *  <i>F + C</i>. This implementation has a large number of configuration
 *  constants, which can be found in <code>ForwardingEngine.h</code>.
 *
 *  <p>Packets in the send queue are sent in FIFO order, with head-of-line
 *  blocking. Because this is a tree collection protocol, all packets are going
 *  to the same destination, and so the ForwardingEngine does not distinguish
 *  packets from one another: packets from CollectionSenderC clients are
 *  treated identically to forwarded packets.</p>
 *
 *  <p>If ForwardingEngine is on top of a link layer that supports
 *  synchronous acknowledgments, it enables them and retransmits packets
 *  when they are not acked. It transmits a packet up to MAX_RETRIES times
 *  before giving up and dropping the packet.</p> 
 *
 *  <p>The ForwardingEngine detects routing loops and tries to correct
 *  them. It assumes that the collection tree is based on a gradient,
 *  such as hop count or estimated transmissions. When the ForwardingEngine
 *  sends a packet to the next hop, it puts the local gradient value in
 *  the packet header. If a node receives a packet to forward whose
 *  gradient value is less than its own, then the gradient is not monotonically
 *  decreasing and there may be a routing loop. When the ForwardingEngine
 *  receives such a packet, it tells the RoutingEngine to advertise its
 *  gradient value soon, with the hope that the advertisement will update
 *  the node who just sent a packet and break the loop.
 *  
 *  <p>ForwardingEngine times its packet transmissions. It differentiates
 *  between four transmission cases: forwarding, success, ack failure, 
 *  and loop detection. In each case, the
 *  ForwardingEngine waits a randomized period of time before sending the next
 *  packet. This approach assumes that the network is operating at low
 *  utilization; its goal is to prevent correlated traffic -- such as 
 *  nodes along a route forwarding packets -- from interfering with itself.
 *
 *  <table>
 *    <tr>
 *      <td><b>Case</b></td>
 *      <td><b>CC2420 Wait (ms)</b></td>
 *      <td><b>Other Wait (ms)</b></td>
 *      <td><b>Description</b></td>
 *    </tr>
 *    <tr>
 *      <td>Forwarding</td>
 *      <td>Immediate</td>
 *      <td>Immediate</td>
 *      <td>When the ForwardingEngine receives a packet to forward and it is not
 *          already sending a packet (queue is empty). In this case, it immediately
 *          forwards the packet.</td>
 *    </tr>
 *    <tr>
 *      <td>Success</td>
 *      <td>16-31</td>
 *      <td>128-255</td>
 *      <td>When the ForwardingEngine successfully sends a packet to the next
 *          hop, it waits this long before sending the next packet in the queue.
 *          </td>
 *    </tr>
 *    <tr>
 *      <td>Ack Failure</td>
 *      <td>8-15</td>
 *      <td>128-255</td>
 *      <td>If the link layer supports acks and the ForwardingEngine did not
 *          receive an acknowledgment from the next hop, it waits this long before
 *          trying a retransmission. If the packet has exceeded the retransmission
 *          count, ForwardingEngine drops the packet and uses the Success timer instead. </td>
 *    </tr>
 *    <tr>
 *      <td>Loop Detection</td>
 *      <td>32-63</td>
 *      <td>512-1023</td>
 *      <td>If the ForwardingEngine is asked to forward a packet from a node that
 *          believes it is closer to the root, the ForwardingEngine pauses its
 *          transmissions for this interval and triggers the RoutingEngine to 
 *          send an update. The goal is to let the gradient become consistent before
 *          sending packets, in order to prevent routing loops from consuming
 *          bandwidth and energy.</td>
 *    </tr>
 *  </table>  
 *
 *  <p>The times above are all for CC2420-based platforms. The timings for
 *  other platforms depend on their bit rates, as they are based on packet
 *  transmission times.</p>

 *  @author Philip Levis
 *  @author Kyle Jamieson
 *  @date   $Date: 2006/06/26 22:55:33 $
 */

#include <ForwardingEngine.h>
#include "CollectionDebugMsg.h"
   
generic module ForwardingEngineP() {
  provides {
    interface Init;
    interface StdControl;
    interface Send[uint8_t client];
    interface Receive[collection_id_t id];
    interface Receive as Snoop[collection_id_t id];
    interface Intercept[collection_id_t id];
    interface Packet;
    interface CollectionPacket;
  }
  uses {
    interface AMSend as SubSend;
    interface Receive as SubReceive;
    interface Receive as SubSnoop;
    interface Packet as SubPacket;
    interface UnicastNameFreeRouting;
    interface SplitControl as RadioControl;
    interface Queue<fe_queue_entry_t*> as SendQueue;
    interface Pool<fe_queue_entry_t> as QEntryPool;
    interface Pool<message_t> as MessagePool;
    interface Timer<TMilli> as RetxmitTimer;
    interface Cache<uint32_t> as SentCache;
    interface TreeRoutingInspect;
    interface PacketAcknowledgements;
    interface Random;
    interface RootControl;
    interface CollectionId[uint8_t client];
    interface AMPacket;
    interface CollectionDebug;
  }
}
implementation {
  /* Starts the retxmit timer with a random number masked by the given
   * mask and added to the given offset.
   */
  static void startRetxmitTimer(uint16_t mask, uint16_t offset);

  /* Keeps track of whether the routing layer is running; if not,
   * it will not send packets. */
  bool running = FALSE;

  /* Keeps track of whether the radio is on; no sense sending packets
   * if the radio is off. */
  bool radioOn = FALSE;

  /* Keeps track of whether an ack is pending on an outgoing packet,
   * so that the engine can work unreliably when the data-link layer
   * does not support acks. */
  bool ackPending = FALSE;

  /* Keeps track of whether the packet on the head of the queue
   * is being used, and control access to the data-link layer.*/
  bool sending = FALSE;

  /* Keep track of the last parent address we sent to, so that
     unacked packets to an old parent are not incorrectly attributed
     to a new parent. */
  am_addr_t lastParent;
  
  /* Network-level sequence number, so that receivers
   * can distinguish retransmissions from different packets. */
  uint8_t seqno;

  enum {
    CLIENT_COUNT = uniqueCount(UQ_COLLECTION_CLIENT)
  };

  /* Each sending client has its own reserved queue entry.
     If the client has a packet pending, its queue entry is in the 
     queue, and its clientPtr is NULL. If the client is idle,
     its queue entry is pointed to by clientPtrs. */

  fe_queue_entry_t clientEntries[CLIENT_COUNT];
  fe_queue_entry_t* clientPtrs[CLIENT_COUNT];

  /* The loopback message is for when a collection roots calls
     Send.send. Since Send passes a pointer but Receive allows
     buffer swaps, the forwarder copies the sent packet into 
     the loopbackMsgPtr and performs a buffer swap with it.
     See sendTask(). */
     
  message_t loopbackMsg;
  message_t* loopbackMsgPtr;

  command error_t Init.init() {
    int i;
    for (i = 0; i < CLIENT_COUNT; i++) {
      clientPtrs[i] = clientEntries + i;
      dbg("Forwarder", "clientPtrs[%hhu] = %p\n", i, clientPtrs[i]);
    }
    loopbackMsgPtr = &loopbackMsg;
    lastParent = call AMPacket.address();
    seqno = 0;
    return SUCCESS;
  }

  command error_t StdControl.start() {
    running = TRUE;
    return SUCCESS;
  }

  command error_t StdControl.stop() {
    running = FALSE;
    return SUCCESS;
  }

  /* sendTask is where the first phase of all send logic
   * exists (the second phase is in SubSend.sendDone()). */
  task void sendTask();
  
  /* ForwardingEngine keeps track of whether the underlying
     radio is powered on. If not, it enqueues packets;
     when it turns on, it then starts sending packets. */ 
  event void RadioControl.startDone(error_t err) {
    if (err == SUCCESS) {
      radioOn = TRUE;
      if (!call SendQueue.empty()) {
        post sendTask();
      }
    }
  }
 
  /* 
   * If the ForwardingEngine has stopped sending packets because
   * these has been no route, then as soon as one is found, start
   * sending packets.
   */ 
  event void UnicastNameFreeRouting.routeFound() {
    post sendTask();
  }

  event void UnicastNameFreeRouting.noRoute() {
    // Depend on the sendTask to take care of this case;
    // if there is no route the component will just resume
    // operation on the routeFound event
  }
  
  event void RadioControl.stopDone(error_t err) {
    if (err == SUCCESS) {
      radioOn = FALSE;
    }
  }

  network_header_t* getHeader(message_t* m) {
    return (network_header_t*)call SubPacket.getPayload(m, NULL);
  }
 
  /*
   * The send call from a client. Return EBUSY if the client is busy
   * (clientPtrs is NULL), otherwise configure its queue entry
   * and put it in the send queue. If the ForwardingEngine is not
   * already sending packets (the RetxmitTimer isn't running), post
   * sendTask. It could be that the engine is running and sendTask
   * has already been posted, but the post-once semantics make this
   * not matter.
   */ 
  command error_t Send.send[uint8_t client](message_t* msg, uint8_t len) {
    network_header_t* hdr;