Appendix D: MySimpleHandshakeMac

MySimpleHandshakeMac.groovy from Section 28.4 :

import org.arl.fjage.*
import org.arl.unet.*
import org.arl.unet.phy.*
import org.arl.unet.mac.*
import org.arl.unet.nodeinfo.*

class MySimpleHandshakeMac extends UnetAgent {

  ////// protocol constants

  private final static int PROTOCOL = Protocol.MAC

  private final static float  RTS_BACKOFF     = 2.seconds
  private final static float  CTS_TIMEOUT     = 5.seconds
  private final static float  BACKOFF_RANDOM  = 5.seconds
  private final static float  MAX_PROP_DELAY  = 2.seconds
  private final static int    MAX_RETRY       = 3
  private final static int    MAX_QUEUE_LEN   = 16

  ////// reservation request queue

  private Queue<ReservationReq> queue = new ArrayDeque<ReservationReq>(MAX_QUEUE_LEN)

  ////// PDU encoder/decoder

  private final static int RTS_PDU = 0x01
  private final static int CTS_PDU = 0x02

  private final static PDU pdu = PDU.withFormat {
    uint8('type')         // RTS_PDU/CTS_PDU
    uint16('duration')    // ms
  }

  ////// protocol FSM

  private enum State {
    IDLE, RTS, TX, RX, BACKOFF
  }

  private enum Event {
    RX_RTS, RX_CTS, SNOOP_RTS, SNOOP_CTS
  }

  private FSMBehavior fsm = FSMBuilder.build {

    int retryCount = 0
    float backoff = 0
    def rxInfo

    state(State.IDLE) {
      action {
        if (!queue.isEmpty()) {
          after(rnd(0, BACKOFF_RANDOM)) {
            setNextState(State.RTS)
          }
        }
        block()
      }
      onEvent(Event.RX_RTS) { info ->
        rxInfo = info
        setNextState(State.RX)
      }
      onEvent(Event.SNOOP_RTS) {
        backoff = RTS_BACKOFF
        setNextState(State.BACKOFF)
      }
      onEvent(Event.SNOOP_CTS) { info ->
        backoff = info.duration + 2*MAX_PROP_DELAY
        setNextState(State.BACKOFF)
      }
    }

    state(State.RTS) {
      onEnter {
        Message msg = queue.peek()
        def bytes = pdu.encode(
          type: RTS_PDU,
          duration: Math.ceil(msg.duration*1000))
        phy << new TxFrameReq(
          to: msg.to,
          type: Physical.CONTROL,
          protocol: PROTOCOL,
          data: bytes)
        after(CTS_TIMEOUT) {
          if (++retryCount >= MAX_RETRY) {
            sendReservationStatusNtf(queue.poll(), ReservationStatus.FAILURE)
            retryCount = 0
          }
          setNextState(State.IDLE)
        }
      }
      onEvent(Event.RX_CTS) {
        setNextState(State.TX)
      }
    }

    state(State.TX) {
      onEnter {
        ReservationReq msg = queue.poll()
        retryCount = 0
        sendReservationStatusNtf(msg, ReservationStatus.START)
        after(msg.duration) {
          sendReservationStatusNtf(msg, ReservationStatus.END)
          setNextState(State.IDLE)
        }
      }
    }

    state(State.RX) {
      onEnter {
        def bytes = pdu.encode(
          type: CTS_PDU,
          duration: Math.round(rxInfo.duration*1000))
        phy << new TxFrameReq(
          to: rxInfo.from,
          type: Physical.CONTROL,
          protocol: PROTOCOL,
          data: bytes)
        after(rxInfo.duration + 2*MAX_PROP_DELAY) {
          setNextState(State.IDLE)
        }
        rxInfo = null
      }
    }

    state(State.BACKOFF) {
      onEnter {
        after(backoff) {
          setNextState(State.IDLE)
        }
      }
      onEvent(Event.SNOOP_RTS) {
        backoff = RTS_BACKOFF
        reenterState()
      }
      onEvent(Event.SNOOP_CTS) { info ->
        backoff = info.duration + 2*MAX_PROP_DELAY
        reenterState()
      }
    }

  } // of FSMBuilder

  ////// agent startup sequence

  private AgentID phy
  private int addr

  @Override
  void setup() {
    register Services.MAC
  }

  @Override
  void startup() {
    phy = agentForService(Services.PHYSICAL)
    subscribe(phy)
    subscribe(topic(phy, Physical.SNOOP))
    add new OneShotBehavior({
      def nodeInfo = agentForService(Services.NODE_INFO)
      addr = get(nodeInfo, NodeInfoParam.address)
    })
    add(fsm)
  }

  ////// process MAC service requests

  @Override
  Message processRequest(Message msg) {
    switch (msg) {
      case ReservationReq:
        if (msg.to == Address.BROADCAST || msg.to == addr)
          return new RefuseRsp(msg, 'Reservation must have a destination node')
        if (msg.duration <= 0 || msg.duration > maxReservationDuration)
          return new RefuseRsp(msg, 'Bad reservation duration')
        if (queue.size() >= MAX_QUEUE_LEN)
          return new Message(msg, Performative.FAILURE)
        queue.add(msg)
        fsm.restart()    // tell fsm to check queue, as it may block if empty
        return new ReservationRsp(msg)
      case ReservationCancelReq:
      case ReservationAcceptReq:
      case TxAckReq:
        return new RefuseRsp(msg, 'Not supported')
    }
    return null
  }

  ////// handle incoming MAC packets

  @Override
  void processMessage(Message msg) {
    if (msg instanceof RxFrameNtf && msg.protocol == PROTOCOL) {
      def rx = pdu.decode(msg.data)
      def info = [from: msg.from, to: msg.to, duration: rx.duration/1000.0]
      if (rx.type == RTS_PDU)
        fsm.trigger(info.to == addr ? Event.RX_RTS : Event.SNOOP_RTS, info)
      else if (rx.type == CTS_PDU)
        fsm.trigger(info.to == addr ? Event.RX_CTS : Event.SNOOP_CTS, info)
    }
  }

  ////// expose parameters that are expected of a MAC service

  final int reservationPayloadSize = 0            // read-only parameters
  final int ackPayloadSize = 0
  final float maxReservationDuration = 65.535

  @Override
  List<Parameter> getParameterList() {            // publish list of all exposed parameters
    return allOf(MacParam)
  }

  boolean getChannelBusy() {                      // considered busy if fsm is not IDLE
    return fsm.currentState.name != State.IDLE
  }

  float getRecommendedReservationDuration() {     // recommended duration: one DATA packet
    return get(phy, Physical.DATA, PhysicalChannelParam.frameDuration)
  }

  ////// utility methods

  private void sendReservationStatusNtf(ReservationReq msg, ReservationStatus status) {
    send new ReservationStatusNtf(
      recipient: msg.sender,
      inReplyTo: msg.msgID,
      to: msg.to,
      from: addr,
      status: status)
  }

}
<<< [Appendix C: Command reference]