/// <returns>Main receive event</returns>
public override Event ReceivePacket(Packet packet)
{
return () => {
switch(packet.type) {
case PacketType.ACK:
ProcessACKPacket(packet);
break;
case PacketType.DATA:
ProcessDataPacket(packet);
break;
default:
// ignore routing packets
break;
}
};
}
// On every ack, adjust the timeout
// On 3DA, reset `seq_num` of the host
public void ProcessAck(Packet pkt, Time current_time)
{
if (pkt.seq_num == 1) { // first packet
AdjustTimeout(current_time - pkt.timestamp, true);
}
else {
AdjustTimeout(current_time - pkt.timestamp, false);
}
if (pkt.seq_num > this.biggest_ack) {
this.biggest_ack = pkt.seq_num;
this.dup_cnt = 0;
reset_seq = false;
}
else if (pkt.seq_num == this.biggest_ack) {
this.dup_cnt++;
if (dup_cnt == 3) { reset_seq = true; }
else { reset_seq = false; }
}
}
// On every timeout, reset `seq_num` of the host
public void ProcessTimeout(Packet pkt, Time current_time)
{
reset_seq = true;
}
// On timeout, set window size to 1, and go into slow start
// When the window size is 1, don't reset slow start thresh. (to 2)
// It just means that the retransmitted packet (after 3DA) has been dropped.
public void ProcessTimeout(Packet pkt, Time current_time)
{
if (window_size != 1.0) {
slow_start_thresh = System.Math.Max(2.0, window_size / 2.0);
window_size = 1.0;
} else {
dup_cnt = 0;
}
reset_seq = true;
slow_start = true;
Simulator.Message("SS:" + this);
}
// On every ack, update avg roundtrip time and its variance.
// If the sequence number of the packet is bigger than the previous,
// adjust the window size accordingly to the state it is in.
// Otherwise, bump up the duplicate count.
// Perform fast retransmit followed by congestion avoidance once you reach 3DA.
public void ProcessAck(Packet pkt, Time current_time)
{
if (pkt.seq_num == 1) { // first packet
AdjustTimeout(current_time - pkt.timestamp, true);
}
else {
AdjustTimeout(current_time - pkt.timestamp, false);
}
if (pkt.seq_num > this.biggest_ack) {
this.biggest_ack = pkt.seq_num;
if (dup_cnt > 2) {
this.dup_cnt = 0;
window_size = slow_start_thresh;
// finished fast recovery
// time for congestion avoidance
slow_start = false;
reset_seq = true;
Simulator.Message(this + ": TCP mode = CA");
}
else {
this.dup_cnt = 0;
if (slow_start) {
window_size++;
if (window_size > slow_start_thresh) {
slow_start = false;
Simulator.Message(this + ": Switching from SS to CA");
}
} else { // Congestion Avoidance
window_size += 1/window_size;
}
reset_seq = false;
}
}
else if (pkt.seq_num == this.biggest_ack) {
this.dup_cnt++;
if (dup_cnt == 2) {
slow_start_thresh = System.Math.Max(2.0, window_size / 2.0);
window_size = 1; // effectively resends a single packet
slow_start = false;
reset_seq = true;
Simulator.Message(this + ": FAST TRANSMIT");
}
else {
//window_size++;
reset_seq = false;
}
}
}
/// <summary>
/// The event where the Link stores the packet in the send buffer (or discards it if the buffer is full).
/// </summary>
/// <remarks>
/// Note: A Link always immediately either accept a packet into the queue or discards it.
/// The packet will be sent asynchronously at some later time.
/// </remarks>
/// <param name='packet'>
/// The packet to be sent along this link
/// </param>
public Event EnqueuePacket(Packet packet)
{
return () => {
if (!this.is_transmitting)
{
TransmitPacket(packet);
//Simulator.Message(name + ":transmitting " + packet);
}
else if (this.buffer_occupancy + packet.size < this.buffer_size)
{
this.buffer.Enqueue(packet);
//Simulator.Message(name + ":queueing " + packet);
}
else
{
this.lStatus.dropped_packets++;
Simulator.Message("Link {0}: buffer {1}/{2}; dropping {3}",
this.name,
this.buffer_occupancy,
this.buffer_size,
packet);
}
//Logger.LogLinkStatus(lStatus);
};
}
private void TransmitPacket(Packet packet)
{
Debug.Assert(!this.is_transmitting, "Bug: Tried to transmit two packets simultaneously");
this.is_transmitting = true;
double trans_duration = packet.size / this.rate;
eqp.Add(eqp.current_time + trans_duration, this.PacketTransmissionComplete());
double arrival_time = eqp.current_time + trans_duration + prop_delay;
eqp.Add(arrival_time, dest.ReceivePacket(packet));
}
/// <returns> /// Event that occurs when this Node receives a packet. /// </returns> public abstract Event ReceivePacket(Packet packet);
/// <summary>
/// Event that router receives a packet.
/// The router will immediately perform a routing-table lookup, and forward the packet along the appropriate link.
/// </summary>
/// <exception cref="InvalidOperationException">
/// Throws an exception if the routing table has not been built yet.
/// You should execute the RecalculateRoutingTableEvent event first.
/// </exception>
public override Event ReceivePacket(Packet packet)
{
return () => {
if(packet.type == PacketType.LINK_STATE_ADVERTISEMENT)
this.ProcessLinkStateAdvertisement(packet);
else
this.ForwardOrdinaryPacket(packet);
};
}
/// <summary>
/// Sends a new packet on all outgoing links.
/// If during this round, an identical packet has already been sent, does nothing.
/// This avoids sending infinite loops of link-state packets.
/// </summary>
public void Send(Packet pkt)
{
if(!already_seen.Contains(pkt)) {
// Simulator.Message("Sending link-state packet {0} on links {1}", pkt, outgoing_links.ToDelimitedString());
foreach(Link l in outgoing_links)
eqp.Add(eqp.current_time, l.EnqueuePacket(pkt));
already_seen.Add(pkt);
}
}
/// <summary>
/// Processes a received link-state advertisement by adding it to the table of known link costs.
/// If the received packet gives us enough information, this triggers recalculation of the routing table.
/// The advertisement will be forwarded on all outgoing links (if not already done).
/// </summary>
private void ProcessLinkStateAdvertisement(Packet pkt)
{
// Simulator.Message("Router {0} received link-state packet for link {1}", this.ip, pkt);
Debug.Assert(pkt.seq_num <= this.routing_seq_num);
if(pkt.seq_num == this.routing_seq_num) { // packet describes current round
Link described_link = Simulator.LinksBySrcDest[Tuple.Create(Simulator.Nodes[pkt.src], Simulator.Nodes[pkt.link_dest])];
Debug.Assert(described_link.cost == pkt.link_cost, "Sanity check failed: received link-state packet claiming incorrect link cost");
if(known_link_costs.ContainsKey(described_link)) {
Debug.Assert(known_link_costs[described_link] == pkt.link_cost);
} else {
known_link_costs.Add(described_link, pkt.link_cost);
}
RecalculateRoutingTableIfEnoughInfo();
link_state_sender.Send(pkt);
} else {
Simulator.Message("Warning: received a link-state advertisement from a previous round {0} (current routing seq num = {1})",
pkt.seq_num, this.routing_seq_num);
}
}
/// <summary>
/// Immediately performs a routing-table lookup and forwards an ordinary packet on the appropriate link.
/// </summary>
private void ForwardOrdinaryPacket(Packet packet)
{
if(routing_table == null)
throw new InvalidOperationException("Cannot route packet before routing table is calculated: " + packet);
//Simulator.Message(packet);
Node next = routing_table[Simulator.Nodes[packet.dest]];
Link to_next = Simulator.LinksBySrcDest[Tuple.Create((Node)this, next)];
///Simulator.Message(ip + ":sending " + to_next + packet);
eqp.Add(eqp.current_time, to_next.EnqueuePacket(packet));
}
/// Sends a packet and registers timeout
private void _SendPacket()
{
var packet = new Packet{
payload_size=Packet.DEFAULT_PAYLOAD_SIZE,
src=this.ip,
dest=this.dest_ip,
type=PacketType.DATA,
seq_num=this.next_seq_num,
timestamp = eqp.current_time
};
double completion_time = eqp.current_time + packet.size / link.rate;
eqp.Add(eqp.current_time, link.EnqueuePacket(packet));
is_busy = true;
this.next_seq_num += 1;
eqp.Add(completion_time, CompleteSend());
eqp.Add(completion_time + this.timeout, CheckTimeout(packet, window_resets));
hStat.flows[0].time = eqp.current_time;
hStat.flows[0].window_size = window_size;
hStat.flows[0].packets_sent++;
//Logger.LogHostStatus(hStat);
}
/// return ack packet for a data packet
private void ProcessDataPacket(Packet packet)
{
if (packet.seq_num == expected_seq_num) {
expected_seq_num++;
}
var ack_p = new Packet{payload_size=Packet.DEFAULT_ACK_SIZE,
src=this.ip,
dest=packet.src,
type=PacketType.ACK,
seq_num=expected_seq_num,
timestamp=packet.timestamp};
// Simulator.Message(name+":"+eqp.current_time+": Sending " + ack_p);
UpdatePacketDelay(eqp.current_time - packet.timestamp);
eqp.Add(eqp.current_time, link.EnqueuePacket(ack_p));
this.flow_rec_stat.received_packets++;
}
/// Process ack packet if it lies on unacknowledged window
private void ProcessACKPacket(Packet packet)
{
if (packet.seq_num >= ack_num && packet.seq_num <= next_seq_num) {
this.tcp_strat.ProcessAck(packet, eqp.current_time);
UpdateTCPState();
if (this.tcp_strat.ResetSeq()) {
window_resets++;
}
}
else {
Simulator.Message("Host {0} dropping ack {1}", this.ip, packet);
}
eqp.Add(eqp.current_time, SendPacket());
}
/// If the packet lies inside the unacknowledged window, process the timeout
private Event CheckTimeout(Packet packet, int resets)
{
return () => {
if (packet.seq_num >= ack_num &&
packet.seq_num < next_seq_num &&
window_resets == resets) {
// timed out
Simulator.Message("Host {0}: packet timed out: {1}", this.ip, packet);
window_resets++;
this.tcp_strat.ProcessTimeout(packet, eqp.current_time);
UpdateTCPState();
eqp.Add(eqp.current_time, SendPacket());
}
};
}