/// <summary>
/// Initializes a new instance of the Nic class using the specified
/// MAC address.
/// </summary>
/// <param name="address">A MAC-48 address to assign to the NIC. If this
/// is null, the NIC is assigned a random MAC address.</param>
protected Nic(MacAddress address = null) {
if (address != null)
MacAddress = address;
else
MacAddress = new MacAddress();
Connector = new Connector();
}
/// <summary>
/// Pierces the cable and wires the specified connector to at the specified position.
/// </summary>
/// <param name="position">The position at which to pierce the cable.</param>
/// <param name="connector">The connector to wire to the cable at the pierced
/// position.</param>
/// <returns>A reference to the C10Base5 instance for chaining.</returns>
/// <exception cref="InvalidOperationException">Another connector has already been
/// installed at the specified position.</exception>
/// <exception cref="InvalidOperationException">As per IEEE 802.3 specification the
/// position at which the cable is pierced must be a multiple of 2.5 metres.</exception>
public C10Base5 Pierce(double position, Connector connector) {
if (connectors.Values.Contains(position))
throw new InvalidOperationException("The position is already taken.");
if (Math.Abs(position % 2.5) > 0.1)
throw new InvalidOperationException("Position must be a multiple of 2.5.");
connectors.Add(connector, position);
connector.Cable = this;
return this;
}
/// <summary>
/// Initializes a new instance of the Bridge class.
/// </summary>
/// <param name="numPorts">The number of I/O ports.</param>
/// <param name="delay">The inherent propagation delay of the bridge.</param>
public Bridge(int numPorts, ulong delay) {
for (var i = 0; i < numPorts; i++) {
var c = new Connector();
c.SignalSense += (sender, e) => OnSignalSense(c);
c.SignalCease += (sender, e) => OnSignalCease(c, sender, e);
ports.Add(c);
// House-keeping.
InitFields(c);
}
}
/// <summary>
/// Creates the needed entries in the various dictionaries for the
/// specified connector.
/// </summary>
/// <param name="connector">The connector to initialize.</param>
void InitFields(Connector connector) {
tx.Add(connector, false);
rx.Add(connector, false);
retransmissionCount.Add(connector, 0);
transmissionData.Add(connector, null);
inputFifo.Add(connector, new CappedQueue<Frame>());
outputFifo.Add(connector, new CappedQueue<Frame>());
waitTime.Add(connector, 0);
isIdle.Add(connector, true);
}
/// <summary>
/// Attach the specified connector to the cable at the specified position.
/// </summary>
/// <param name="position">The position at which to connect the connector to the
/// cable.</param>
/// <param name="connector">The connector to connect to the cable at the specified
/// position.</param>
/// <exception cref="InvalidOperationException">Another connector has already been
/// installed at the specified position.</exception>
/// <exception cref="InvalidOperationException">As per 10BASE2 specification the
/// position at which a station is connected must be a multiple of 0.5 metres.
/// </exception>
public void Attach(double position, Connector connector) {
if (connectors.Values.Contains(position))
throw new InvalidOperationException("The position is already taken.");
if (Math.Abs(position % 0.5) > .0)
throw new InvalidOperationException("Position must be a multiple of 0.5.");
if (connectors.ContainsKey(connector))
throw new InvalidOperationException("Connector is already attached at " +
connectors[connector] + ".");
connectors.Add(connector, position);
connector.Cable = this;
}
/// <summary>
/// Invokes the specified action for every connector within the
/// collision domain, excluding those connected through the specified
/// inport.
/// </summary>
/// <param name="inport">The port through which the signal is being
/// received.</param>
/// <param name="action">The action to invoke.</param>
void Repeat(Connector inport, Action<Connector, ulong> action) {
foreach (var c in ports) {
if (!c.IsConnected || c == inport)
continue;
var pos = c.Cable.Connectors[c];
foreach (var pair in c.Cable.Connectors) {
if (pair.Key == c)
continue;
var dist = Math.Abs(pos - pair.Value);
var propDelayNs = (ulong) (1000000000 *
(dist / c.Cable.PropagationSpeed));
action(pair.Key, Delay + propDelayNs);
}
}
}
/// <summary>
/// Initializes a new instance of the Hub class.
/// </summary>
/// <param name="numPorts">The number of I/O ports.</param>
/// <param name="delay">The inherent propagation delay of the hub.</param>
public Hub(int numPorts, ulong delay) {
for (var i = 0; i < numPorts; i++) {
var c = new Connector();
c.SignalSense += (sender, e) => {
Repeat(c, (other, propDelay) =>
Simulation.AddEvent(new SignalSenseEvent(propDelay,
other, sender)));
};
c.SignalCease += (sender, e) => {
Repeat(c, (other, propDelay) =>
Simulation.AddEvent(new SignalCeaseEvent(propDelay,
other, e.Data, sender)));
};
ports.Add(c);
}
}
/// <summary>
/// Starts the actual data transfer.
/// </summary>
/// <param name="connector"></param>
/// <param name="data">The data to transmit.</param>
void StartTransmission(Connector connector, byte[] data) {
// If the medium is no longer idle at this point, start over.
if (rx[connector]) {
Transmit(connector, data);
return;
}
WritePhy("Starting transmission.");
tx[connector] = true;
transmissionData[connector] = data;
connector.Transmit(data);
}
/// <summary>
/// Simulates the transmission of data from the specified source.
/// </summary>
/// <param name="source">The connector from which data is being transmitted.</param>
/// <param name="data">The data that is being transmitted from the source.</param>
public void Transmit(Connector source, byte[] data) {
source.ThrowIfNull("source");
data.ThrowIfNull("data");
var position = connectors[source];
// Simulate physical frame corruption.
if (HasNoise)
data = DistortSignal(data);
// Calculate transmission time = Size / Bitrate.
var transTimeNs = (ulong) (1000000000 *
(data.Length * 8 / (double) Bitrate));
// Calculate events for each device on the cable.
foreach (var pair in connectors) {
var distance = Math.Abs(position - pair.Value);
// Propagation delay in nanoseconds.
var propDelayNs = (ulong) (1000000000 *
(distance / PropagationSpeed));
var deliveryTimeNs = propDelayNs + transTimeNs;
Simulation.AddEvent(
new SignalSenseEvent(propDelayNs, pair.Key, source));
Simulation.AddEvent(
new SignalCeaseEvent(deliveryTimeNs, pair.Key, data, source));
}
}
/// <summary>
/// Simulates the transmission of a Jam signal.
/// </summary>
/// <param name="source">The source sending the Jam signal.</param>
/// <returns>The time it takes to transmit the Jam signal, in nanoseconds.</returns>
public ulong Jam(Connector source) {
Simulation.RemoveEvents(ev => ev is SignalCeaseEvent &&
ev.Sender == source);
var position = connectors[source];
// Calculate the transmission time.
var transTimeNs = (ulong) (1000000000 * (48 / (double) Bitrate));
// Calculate the propagation delay and delivery time for each
// NIC within the collision domain.
foreach (var pair in connectors) {
var distance = Math.Abs(position - pair.Value);
var propDelayNs = (ulong) (1000000000 *
(distance / PropagationSpeed));
var deliveryTimeNs = propDelayNs + transTimeNs;
Simulation.AddEvent(
new SignalCeaseEvent(deliveryTimeNs, pair.Key, null, source));
}
return transTimeNs;
}
/// <summary>
/// Invoked om behalf of PHY whenever a frame has been transmitted.
/// </summary>
void OnDataTransmitted(Connector connector) {
WriteMac("Finished transmitting Ethernet frame.");
isIdle[connector] = true;
waitTime[connector] = Simulation.Time + interframeGapTime(connector);
}
/// <summary>
/// Invoked on behalf of PHY whenever new data has been received.
/// </summary>
/// <param name="connector"></param>
/// <param name="data">The data that was received.</param>
void OnDataReceived(Connector connector, byte[] data) {
data.ThrowIfNull("data");
WriteMac("Received an Ethernet frame.");
waitTime[connector] = Simulation.Time + interframeGapTime(connector);
var frame = Frame.Deserialize(data);
// Compute checksum and compare to the one contained in the frame.
var fcs = Frame.ComputeCheckSequence(frame);
if (fcs != frame.CheckSequence) {
WriteMac("Detected a bad frame check sequence, discarding.");
return;
}
// Remember the port through which the frame came in.
forwardTable[frame.Source] = connector;
// If we know the destination and it's on the same port as the
// source, discard the frame.
if (forwardTable.ContainsKey(frame.Destination)) {
if (forwardTable[frame.Source] == forwardTable[frame.Destination])
return;
}
// Start emptying the FIFO, if we're not already doing it.
if (emptyingFifos == false)
Simulation.Callback(0, EmptyFifos);
// Enqueue the data.
inputFifo[connector].Enqueue(frame);
}
/// <summary>
/// Performs the exponential backoff algorithm of CSMA/CD.
/// </summary>
/// <param name="connector"></param>
/// <param name="deltaTime"></param>
void ExponentialBackoff(Connector connector, ulong deltaTime) {
retransmissionCount[connector]++;
if (retransmissionCount[connector] >= maxRetransmissions) {
AbortTransmission(connector);
} else {
// Wait a random number of slot-times, with a slot-time being
// defined as the transmission time of 512 bits.
// (Cmp, "Computer Networks", 5th Ed., A. Tanenbaum, p.285)
var c = random.Next((int) Math.Pow(2,
Math.Min(retransmissionCount[connector], maxExponentiation)));
// (Ex., the slot-time on 10Mbps Ethernet is 51.2µsec)
var slotTime = (ulong) ((512 / (double)
configuredBitrate(connector)) * 1000000000);
var _waitTime = (ulong) c * slotTime;
WritePhy("Waiting for " + _waitTime + " (" + c +
" slot times), " + retransmissionCount + ".Try, Total = " +
(deltaTime + _waitTime));
Simulation.Callback(deltaTime + _waitTime,
() => Transmit(connector, transmissionData[connector]));
}
}
int configuredBitrate(Connector connector) {
return connector.Cable.Bitrate;
}
/// <summary>
/// Aborts a scheduled data transmission.
/// </summary>
void AbortTransmission(Connector connector) {
WritePhy("Transmission failed! Maximum retransmission " +
"threshold reached.");
// Reset retransmission counter.
retransmissionCount[connector] = 0;
}
ulong interframeGapTime(Connector connector) {
return (ulong) ((96 / (double) configuredBitrate(connector)) *
1000000000);
}
/// <summary>
/// Transmits the specified data.
/// </summary>
/// <param name="connector"></param>
/// <param name="data">The data to transmit.</param>
void Transmit(Connector connector, byte[] data) {
// Defer transmission until medium becomes idle.
if (rx[connector]) {
// Poll medium about every 10µs.
var timeout = (ulong) (10000 + random.Next(5000));
WritePhy("Deferring transmission, next try at " + timeout);
Simulation.Callback(timeout, () => Transmit(connector, data));
} else {
// Must wait another interframe-gap, before we can proceed.
Simulation.Callback(interframeGapTime(connector),
() => StartTransmission(connector, data));
}
}
/// <summary>
/// Invoked whenever the carrier signal ceases.
/// </summary>
/// <param name="connector">The connector which is no longer
/// sensing a signal.</param>
/// <param name="sender"></param>
/// <param name="e"></param>
void OnSignalCease(Connector connector, object sender, SignalCeaseEventArgs e) {
if (tx[connector])
WritePhy("Finished transmitting bits.");
rx[connector] = false;
tx[connector] = false;
// Hand data to MAC-layer.
if (e.IsJam) {
WritePhy("Receiving a jam signal.");
return;
}
if (sender == connector)
OnDataTransmitted(connector);
else
OnDataReceived(connector, e.Data);
}
/// <summary>
/// Invoked whenever the receiver senses a signal.
/// </summary>
/// <param name="connector">The connector sensing a signal.</param>
void OnSignalSense(Connector connector) {
WritePhy("Sensing a carier.");
if (rx[connector] && tx[connector]) {
// Collision.
WritePhy("Collision detected.");
var jamTime = connector.Jam();
ExponentialBackoff(connector, jamTime);
} else {
rx[connector] = true;
}
}