def _trySendingFrame(self):
"""Only send if no carrier is sensed and we are not in backoff."""
if self._transmitting or self._outstandingFrame:
# Another frame is currently being transmitted. Wait for next call.
return
if not self._transmitQueue:
# Nothing to transmit.
return
if self._backingOff:
# Still waiting backoff
return
if self._device.phy.carrierSense():
# Channel is occupied. Do backoff. *** COLLISION AVOIDANCE ***
self._backingOff = True
SCHEDULE(self._computeBackoff(), self._endBackoff)
ACTIVITY_INDICATION(self, "tx", "CA backoff", "darkblue", 1, 2)
return
type, dstAddr, bitstream = self._transmitQueue.pop(0)
if type == self.ACK:
# Create a new Ack frame and send it.
ACTIVITY_INDICATION(self, "tx", "ACK/NAK", "grey", 0, 0)
self._phySendFrame(dstAddr=dstAddr, data="")
else:
if type == self.RETR:
self.packetRetransmissions += 1
ACTIVITY_INDICATION(self, "tx", "Resend", "orange", 0, 0)
else:
ACTIVITY_INDICATION(self, "tx", "Send", "yellow", 0, 0)
self._resetBackoff()
self.packetsSent += 1
self._retransmissionTimer = SCHEDULE(self.retransmissionTimeout,
self._timeout)
self._outstandingFrame = self._phySendFrame(dstAddr, bitstream)
def _backoff(self):
"""Compute backoff and schedule retransmission.
This method is called after the end of the jam transmission. In half
duplex mode, it does the following:
- compute a backoff
- enter backoff mode
- schedule the retransmission of the frame.
If the maximum number of collisions is already reached, abandon the
frame and signal an error to the upper layer.
"""
ACTIVITY_INDICATION(self, "tx", "backoff", "blue", 1, 2)
self._jamming = False
if self._transmissionAttemps >= 16:
# Transmission failed. Update statistics, inform dl and clean up
SCHEDULE(0.0, self._niu.dl.sendStatus,
(_EXCESSIVE_COLLISION_ERROR, self._sendBuffer))
self.excessiveCollisions += 1
print "Excessive collisions"
self._transmissionAttemps = 0
self._sendBuffer = None
self._niu.XOFF = False
return
k = min(10, self._transmissionAttemps)
r = int(random() * (1 << k))
if self._niu.phy.getDataRate() == 1000e6:
backoff = r * self._GIGA_SLOTTIME * self._niu.phy.bittime()
else:
backoff = r * self._SLOTTIME * self._niu.phy.bittime()
SCHEDULE(backoff, self._mediumAccess)
def send(self, bitstream):
"""Simulate the transmission of the data on the medium.
Schedule the call to inform the DL entity when finished.
Arguments:
bitstream:Bitstream -- Block of data to transmit onto the medium.
Return value: None.
"""
self._niu.medium.startTransmission(self._niu)
transmissionDelay = len(bitstream) * 8 / self._dataRate
SCHEDULE(transmissionDelay, self._niu.medium.completeTransmission,
(self._niu, bitstream))
SCHEDULE(transmissionDelay, self._niu.dl.sendStatus, (0, bitstream))
def send(self, bitstream):
"""Encapsulate the data into a frame and send it to the phy layer.
May only be called if self._device.XOFF is False, i.e. if the
device is ready to accept a new data packet from the higher layer.
"""
# Make sure there is no other packet already in transit.
assert (self._device.XOFF == False and not self._sendBuffer)
# Block any new transmission until this packet has been acknowledged
self._device.XOFF = True
# Create a new frame with CRC and sequence numbers.
frame = self._newFrame()
frame.SN = self._VS
self._VS = (self._VS + 1) % 2
frame.RN = self._VR
frame.data = bitstream
checksum = crc32(frame.serialize()[:-4]) & ((1L << 32) - 1)
frame.FCS = checksum
# Set the retransmission timer
self._sendBuffer = frame
self._retransmissionTimer = SCHEDULE(self.retransmissionTimeout,
self._timeout)
# Sent the frame
ACTIVITY_INDICATION(self, "tx", "Send", "yellow", 0, 0)
self.packetsSent += 1
self._device.phy.send(frame.serialize())
return 0
def _trySendingFrame(self):
"""Send the next frame waiting in the transmitQ, if there is any."""
if self._transmitting or self._outstandingFrame:
# Another frame is currently being transmitted. Wait for next call.
return
if not self._transmitQueue:
# Nothing to transmit.
return
type, dstAddr, bitstream = self._transmitQueue.pop(0)
if type == self.ACK:
# Create a new Ack frame and send it.
ACTIVITY_INDICATION(self, "tx", "ACK/NAK", "grey", 0, 0)
self._phySendFrame(dstAddr=dstAddr, data="")
else:
if type == self.RETR:
self.packetRetransmissions += 1
ACTIVITY_INDICATION(self, "tx", "Resend", "orange", 0, 0)
else:
ACTIVITY_INDICATION(self, "tx", "Send", "yellow", 0, 0)
self._resetBackoff()
self.packetsSent += 1
self._retransmissionTimer = SCHEDULE(self.retransmissionTimeout,
self._timeout)
self._outstandingFrame = self._phySendFrame(dstAddr, bitstream)
def _timeout(self):
"""Called when a retransmission timeout occurs."""
ACTIVITY_INDICATION(self, "tx", "TIMEOUT")
self._retransmissionTimer = None
self._consecutiveCollisions += 1
self._backingOff = True
ACTIVITY_INDICATION(self, "tx", "Retr backoff", "blue", 1, 2)
SCHEDULE(self._computeBackoff(), self._endBackoff)
def _trySendingFrame(self):
"""Send the next frame waiting in the sendBuffer, if there is any."""
if self._transmitting:
# Another frame is currently being transmitted. Wait for next call.
return
if not self._transmitQueue:
# Nothing to transmit.
return
type, sn = self._transmitQueue.pop(0)
if type == self.ACK or type == self.SREJ:
# Create a new Ack frame and send it.
ack = self._newFrame()
ack.SN = self._SNmax # Allowed since payload is empty
ack.RN = sn
if type == self.SREJ:
ack.SREJ = 1
ACTIVITY_INDICATION(self, "tx",
"Send SREJ RN=%s" % str(ack.RN), "red", 0,
0)
else:
ACTIVITY_INDICATION(self, "tx", "Send ACK RN=%s" % str(ack.RN),
"grey", 0, 0)
checksum = crc32(ack.serialize()[:-4]) & ((1L << 32) - 1)
ack.FCS = checksum
self._transmitting = True
self._device.phy.send(ack.serialize())
else:
assert (type == self.FIRSTTR or type == self.RETR)
# Create a new data packet and send it
bitstream = self._sendBuffer[sn]
frame = self._newFrame()
frame.SN = sn
frame.RN = self._VR
frame.data = bitstream
checksum = crc32(frame.serialize()[:-4]) & ((1L << 32) - 1)
frame.FCS = checksum
# Set the retransmission timer
if sn in self._retransmissionTimer:
timer = self._retransmissionTimer.pop(sn)
CANCEL(timer)
self._retransmissionTimer[sn] = SCHEDULE(
self.retransmissionTimeout, self._timeout, (sn, ))
# Send the frame and update the statistics
if type == self.RETR:
self.packetRetransmissions += 1
ACTIVITY_INDICATION(self, "tx", "Retr SN=%s" % str(frame.SN),
"orange", 0, 0)
else:
ACTIVITY_INDICATION(self, "tx", "Send SN=%s" % str(frame.SN),
"yellow", 0, 0)
self.packetsSent += 1
self._transmitting = True
self._device.phy.send(frame.serialize())
def send(self, bitstream):
"""Accept a block of data and simulate transmission on the medium.
Called by the MAC layer to transmit a block of data. Can be called
multiple times while Phy.transmitting is active (). In this case, if the
previous block has not yet been completely transmitted onto the medium,
the remaining data is discarded and the transmission continues with the
new data. Therefore, the MAC should call this method only after having
received a MAC.sendStatus notification or if a collision
has been detected and the MAC wants to stop the transmission of data
and continue with a jam signal.
Arguments:
bitstream:Bitstream -- Block of data to transmit onto the medium.
Return value: None.
"""
if self._transmitting == False:
raise RuntimeError("Attempt to transmit without previously "
"activating transmission on NIU: " +
self._niu._node.hostname + "." +
self._niu.devicename + ".phy")
if self._transmittedData == None:
# New transmission
self._transmittedData = bitstream
self._transmitStartTime = TIME()
self._niu.medium.startTransmission(self._niu)
transmissionDelay = len(bitstream) * 8 / self._dataRate
self._completeTxEventId = SCHEDULE(transmissionDelay,
self._completeTransmission)
if self._receiveActivities > 0:
self._niu.mac.collisionDetect()
else:
# Interrupt current transmission and send new data
bytelen = int(
((TIME() - self._transmitStartTime) * self._dataRate + 0.05) /
8)
self._transmittedData = self._transmittedData[0:bytelen] + bitstream
CANCEL(self._completeTxEventId)
transmissionDelay = len(bitstream) * 8 / self._dataRate
self._completeTxEventId = SCHEDULE(transmissionDelay,
self._completeTransmission)
def _retransmit(self):
"""Retransmits the current frame.
Called either because of a negative ack or by a retransmission timeout.
"""
ACTIVITY_INDICATION(self, "tx", "Retransmit", "orange", 0, 0)
if self._retransmissionTimer:
CANCEL(self._retransmissionTimer)
self._retransmissionTimer = SCHEDULE(self.retransmissionTimeout,
self._timeout)
self.packetRetransmissions += 1
self.packetsSent += 1
self._device.phy.send(self._sendBuffer.serialize())
def _checkAck(self, frame):
"""Look if the frame contains an ACK and handle it."""
if self._outstandingFrame != None: # We are waiting for an ACK
if frame.RN == (self._VS[frame.SrcAddr] + 1) % 2:
# POSITIVE ACKNOWLEDGEMENT
ACTIVITY_INDICATION(self, "rx", "ACK ok")
self._outstandingFrame = None
if self._retransmissionTimer:
CANCEL(self._retransmissionTimer)
self._retransmissionTimer = None
self._VS[frame.SrcAddr] = frame.RN
# Do a backoff. *** COLLISION AVOIDANCE ***
self._backingOff = True
SCHEDULE(self._computeBackoff(), self._endBackoff)
ACTIVITY_INDICATION(self, "tx", "CA backoff", "darkblue", 1, 2)
def _sendPacket(self):
"""Send PDUs to the lower layer until the whole page is transmitted.
At the end, start a new OFF period by calling generate."""
length = min(self._pageSize, self._pduSize)
bitstream = self._uniqueBitstream(length)
self.send(bitstream)
self.octetsTransmitted += length
self.pdusTransmitted += 1
self._pageSize -= length
if self._pageSize > 0:
delay = (self._pduSize*8.0) / self._onRate
SCHEDULE(delay, self._sendPacket)
else:
self.pagesTransmitted += 1
self.generate()
def completeTransmission(self, txNIU, data):
"""Finish a transmission and deliver the data to receiving NIUs.
By calling this method, a phy layer entity of an attached NIU
indicates that it has finished the transmission previously started
by calling startTransmission. The data provided to the medium is
delivered, after a propagation delay, to the phy entities of
attached NIUs by calling phy.receive.
Arguments:
txNIU:NIU -- Transmitting NIU
data:Bitstream -- Transmitted data
Return value: None.
"""
for rxNIU, rxPos in self._niuDict.items():
if rxNIU != txNIU:
propDelay = self._distances[(txNIU, rxNIU)] / self.signalSpeed
SCHEDULE(propDelay, rxNIU.phy.receive, (data, ))
def startTransmission(self, txNIU):
"""Start a transmission on the medium.
A phy protocol entity calls this method to indicate that it
starts the transmission of a signal. The other NIU is
informed, after the propagation delay, that a new transmission
has started by calling the method phy.newChannelActivity of
its phy entity. No data is actually transmitted. This will be
done by the function completeTransmission, which is called by
the phy layer entity at the end of the transmission.
Arguments:
niu:NIU -- Transmitting NIU
Return value: None.
"""
txPos = self._niuDict[txNIU]
for rxNIU, rxPos in self._niuDict.items():
if rxNIU != txNIU:
propDelay = abs(rxPos - txPos) / self.signalSpeed
SCHEDULE(propDelay, rxNIU.phy.newChannelActivity)
def sendStatus(self, status, bitstream):
"""Terminate the transmission, inform dl, and clean up.
This method is called from the phy layer, when a transmission
previously initiated with PHY.send terminates.
First check if we are sending a jam. In this case, the jam
transmission has completed. Switch of the transmission and call the
backoff method.
If not jamming, terminate the transmission, update the statistics,
clean up and inform the upper layer.
A status==0 indicates success. Any other status indicates an error.
"""
self._latestTransmitActivity = TIME()
if self._jamming:
ACTIVITY_INDICATION(self, "tx")
self._niu.phy.transmitting(False)
self._backoff()
return
ACTIVITY_INDICATION(self, "tx")
self._niu.phy.transmitting(False) # Terminate the transmission
if not status:
self.framesTransmittedOK += 1
self.octetsTransmittedOK += len(self._sendBuffer.data)
if self._transmissionAttemps > 2:
self.multipleCollisionFrames += 1
if self._transmissionAttemps == 2:
self.singleCollisionFrames += 1
else:
# Discard the frame and inform DL (LLC)
self.octetsTransmittedError += len(self._sendBuffer.data)
status = _UNKNOWN_TRANSMISSION_ERROR
SCHEDULE(0.0, self._niu.dl.sendStatus, (status, self._sendBuffer))
self._transmissionAttemps = 0
self._sendBuffer = None
self._niu.XOFF = False
def generate(self):
length = max(9,int(self._pduSizeRNG()))
self.send(self._uniqueBitstream(length))
self.octetsTransmitted += length
self.pdusTransmitted += 1
SCHEDULE(self._interarrivalRNG(), self.generate)
def _timeout(self):
"""Called when a retransmission timeout occurs."""
ACTIVITY_INDICATION(self, "tx", "TIMEOUT")
self._retransmissionTimer = None
self._consecutiveCollisions += 1
SCHEDULE(self._computeBackoff(), self._retransmit)
def start(self):
SCHEDULE(self.interval, self.generate)
def generate(self):
"""Schedule a new page transmission after a random OFF time."""
offTime = self._offTimeRNG()
offTime = min(offTime, self._offTimeMax)
offTime = max(offTime, self._offTimeMin)
SCHEDULE(offTime, self._sendPage)
def _mediumAccess(self):
"""Acquire the transmit medium, transmit the frame and inform dl.
This function tries to transmit a current frame according to the
CSMA/CD algorithm, as described in the standard, Section 4.2.3.2.
The following elements of the standard are implemented:
- Half duplex transmission: CSMA/CD
- Full duplex transmission
- Carrier sense (in half duplex)
- Interframe spacing (in half and full duplex)
- Collision detection and enforcement through jam (in half duplex)
- Exponential backoff and retransmission (half duplex)
- Carrier extension (in half duplex for data rate > 100 Mb/s
The following elements are not implemented:
- Frame bursting (used for data rates > 100 Mb/s).
"""
assert (self._sendBuffer != None)
if self._niu.phy.getDuplexMode() == FULL_DUPLEX:
# Transmission without contention. Only respect interframe gap
gaptime = self._INTERFRAME_GAP * self._niu.phy.bittime()
currentgap = TIME() - self._latestTransmitActivity
if currentgap < gaptime:
ACTIVITY_INDICATION(self, "tx", "gaptime", "grey", 3, 2)
SCHEDULE(gaptime - currentgap, self._mediumAccess)
return
self._transmissionAttemps += 1
ACTIVITY_INDICATION(self, "tx", "send FD", "green", 0, 0)
self._niu.phy.transmitting(activate=True)
self._niu.phy.send(self._sendBuffer.serialize())
return
else: # Transmission in half duplex mode
# 1. Carrier sense
if self._niu.phy.carrierSense():
ACTIVITY_INDICATION(self, "tx", "carrierSense", "blue", 3, 2)
self._waitingForIdleChannel = True
# Wait until channel activities end. The MAC.channelIdle
# method will call us then
return
self._waitingForIdleChannel = False
# 2. Interframe gap
gaptime = self._INTERFRAME_GAP * self._niu.phy.bittime()
currentgap = TIME() - max(self._latestTransmitActivity,
self._latestReceiveActivity)
if gaptime - currentgap > self._niu.phy.bittime() / 100:
ACTIVITY_INDICATION(self, "tx", "gaptime", "grey", 3, 2)
gapjitter = gaptime * random() / 100 # Avoid dicrete synchro.
SCHEDULE(gaptime - currentgap + gapjitter, self._mediumAccess)
return
# 3. Here we go. Initiate the transmission. Wait for the
# transmissionCompleted or collisionDetect signal
self._transmissionAttemps += 1
ACTIVITY_INDICATION(self, "tx", "send HD", "green", 0, 0)
self._niu.phy.transmitting(activate=True)
self._niu.phy.send(self._sendBuffer.serialize())
return
def generate(self):
self.send(self._uniqueBitstream(self._pduSize))
self.octetsTransmitted += self._pduSize
self.pdusTransmitted += 1
SCHEDULE(self._interarrival, self.generate)
def generate(self):
data = 'y'*self.length # A string 'xxxxx' of the correct length
packet = data + self.checksum(data)
self.send(packet)
SCHEDULE(self.interval, self.generate)
