Multiple Access Protocols

Multiple Access Protocols

• Single shared broadcast channel
• Two or more simultaneous transmissions by nodes
• Multiple Access Protocol
• • Protocol for how nodes share channel
• • In general, no extra control channel
• • In many cases, no central coordinator

Random Access Protocols

• When node has packet to send
• • Detect whether channel is idle or busy
• • Transmit at full channel data rate R
• • No a prior coordination among nodes
• Two or more transmitting nodes -> collision
• Random access MAC protocol specifies
• • How to detect collisions & recover from collisions
• Examples of random access MAC protocols
• • Slotted ALOHA, ALOHA
• • CSMA/CD, CSMA/CA

CSMA (Carrier Sense Multiple Access)

• CSMA: Listen before transmit
• • If channel sensed idle, transmit entire frame
• • If channel sensed busy, defer transmission
• CSMA/CD (Collision Detection)
• • Collisions detected within short time
• • Colliding transmissions aborted, reducing channel wastage
• • Collision detection
    Easy in wired LANs
    Difficult in wireless LANs

CSMA Models in ns-3

• in src/csma diretory
  

Bus Topology Example

• P2P Node Creation

NodeContainer p2pNodes;
p2pNodes.Create (2);

• CSMA Node Creation

NodeContainer csmaNodes;
csmaNodes.Add (p2pNodes.Get (1));
csmaNodes.Create (nCsma);

/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include "ns3/core-module.h"
#include "ns3/network-module.h"
#include "ns3/csma-module.h"
#include "ns3/internet-module.h"
#include "ns3/point-to-point-module.h"
#include "ns3/applications-module.h"
#include "ns3/ipv4-global-routing-helper.h"

// Default Network Topology
//
//       10.1.1.0
// n0 -------------- n1   n2   n3   n4
//    point-to-point  |    |    |    |
//                    ================
//                      LAN 10.1.2.0


using namespace ns3;

NS_LOG_COMPONENT_DEFINE ("SecondScriptExample");

int 
main (int argc, char *argv[])
{
  bool verbose = true;
  uint32_t nCsma = 3;

  CommandLine cmd;
  cmd.AddValue ("nCsma", "Number of \"extra\" CSMA nodes/devices", nCsma);
  cmd.AddValue ("verbose", "Tell echo applications to log if true", verbose);

  cmd.Parse (argc,argv);

  if (verbose)
    {
      LogComponentEnable ("UdpEchoClientApplication", LOG_LEVEL_INFO);
      LogComponentEnable ("UdpEchoServerApplication", LOG_LEVEL_INFO);
    }

  nCsma = nCsma == 0 ? 1 : nCsma;

  NodeContainer p2pNodes;
  p2pNodes.Create (2);

  NodeContainer csmaNodes;
  csmaNodes.Add (p2pNodes.Get (1));
  csmaNodes.Create (nCsma); //total 5, maded 3 node before

  PointToPointHelper pointToPoint;
  pointToPoint.SetDeviceAttribute ("DataRate", StringValue ("5Mbps"));
  pointToPoint.SetChannelAttribute ("Delay", StringValue ("2ms"));

  NetDeviceContainer p2pDevices;
  p2pDevices = pointToPoint.Install (p2pNodes);

  CsmaHelper csma;
  csma.SetChannelAttribute ("DataRate", StringValue ("100Mbps"));
  csma.SetChannelAttribute ("Delay", TimeValue (NanoSeconds (6560)));

  NetDeviceContainer csmaDevices;
  csmaDevices = csma.Install (csmaNodes);

  InternetStackHelper stack;
  stack.Install (p2pNodes.Get (0));
  stack.Install (csmaNodes);

  Ipv4AddressHelper address;
  address.SetBase ("10.1.1.0", "255.255.255.0");
  Ipv4InterfaceContainer p2pInterfaces;
  p2pInterfaces = address.Assign (p2pDevices);

  address.SetBase ("10.1.2.0", "255.255.255.0");
  Ipv4InterfaceContainer csmaInterfaces;
  csmaInterfaces = address.Assign (csmaDevices);

  UdpEchoServerHelper echoServer (9); //9 is port number

  ApplicationContainer serverApps = echoServer.Install (csmaNodes.Get (nCsma));
  serverApps.Start (Seconds (1.0));
  serverApps.Stop (Seconds (10.0));

  UdpEchoClientHelper echoClient (csmaInterfaces.GetAddress (nCsma), 9); //get lan address of n2, n3, n4
  echoClient.SetAttribute ("MaxPackets", UintegerValue (1));
  echoClient.SetAttribute ("Interval", TimeValue (Seconds (1.0)));
  echoClient.SetAttribute ("PacketSize", UintegerValue (1024));

  ApplicationContainer clientApps = echoClient.Install (p2pNodes.Get (0));
  clientApps.Start (Seconds (2.0));
  clientApps.Stop (Seconds (10.0));

  Ipv4GlobalRoutingHelper::PopulateRoutingTables ();

  pointToPoint.EnablePcapAll ("second2");
  csma.EnablePcap ("second2", csmaDevices.Get (1), true);

  Simulator::Run ();
  Simulator::Destroy ();
  return 0;
}

• 참고) /ns-3.29/examples/tutorial directory에 예제 코드 있음

Bridge Model in ns-3

• in src/bridge

Star Topology Example

• Node Creation
• • NodeContainer for terminal(hose) nodes

NodeContainer terminals;
terminals.Create (4);

• • NodeContainer for switch nodes

NodeContainer csmaSwitch;
csmaSwitch.Create (1);

• CSMA Link Creation

for (int i = 0; i < 4; i++)
{
	NetDeviceContainer link = csma.Install (NodeContainer (terminals.Get (i), csmaSwitch));
    terminalDevices.Add (link.Get (0));
    switchDevices.Add (link.Get (1));
}

/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

// Network topology
//
//        n0     n1
//        |      | 
//       ----------
//       | Switch |
//       ----------
//        |      | 
//        n2     n3
//
//
// - CBR/UDP flows from n0 to n1 and from n3 to n0
// - DropTail queues 
// - Tracing of queues and packet receptions to file "csma-bridge.tr"

#include <iostream>
#include <fstream>

#include "ns3/core-module.h"
#include "ns3/network-module.h"
#include "ns3/applications-module.h"
#include "ns3/bridge-module.h"
#include "ns3/csma-module.h"
#include "ns3/internet-module.h"

using namespace ns3;

NS_LOG_COMPONENT_DEFINE ("CsmaBridgeExample");

static void
Rxtime (std::string context, Ptr<const Packet> p, const Address &a)
{
    static double bytes1, bytes2 = 0;
    if (context == "Flow1"){
        bytes1 += p->GetSize();
        NS_LOG_UNCOND("1\t" <<Simulator::Now().GetSeconds()
                <<"\t"<<bytes1*8/1000000/(Simulator::Now().GetSeconds()-1));
    }else if(context == "Flow2"){
        bytes2 += p->GetSize();
        NS_LOG_UNCOND("2\t" <<Simulator::Now().GetSeconds()
                <<"\t"<<bytes2*8/1000000/(Simulator::Now().GetSeconds()-1));
    }
}

int 
main (int argc, char *argv[])
{
  //
  // Users may find it convenient to turn on explicit debugging
  // for selected modules; the below lines suggest how to do this
  //
#if 0 
  LogComponentEnable ("CsmaBridgeExample", LOG_LEVEL_INFO);
#endif

  //
  // Allow the user to override any of the defaults and the above Bind() at
  // run-time, via command-line arguments
  //
  CommandLine cmd;
  cmd.Parse (argc, argv);

  //
  // Explicitly create the nodes required by the topology (shown above).
  //
  NS_LOG_INFO ("Create nodes.");
  NodeContainer terminals;
  terminals.Create (4);

  NodeContainer csmaSwitch;
  csmaSwitch.Create (1);

  NS_LOG_INFO ("Build Topology");
  CsmaHelper csma;
  csma.SetChannelAttribute ("DataRate", DataRateValue (5000000));
  csma.SetChannelAttribute ("Delay", TimeValue (MilliSeconds (2)));

  // Create the csma links, from each terminal to the switch

  NetDeviceContainer terminalDevices;
  NetDeviceContainer switchDevices;

  for (int i = 0; i < 4; i++)
    {
      NetDeviceContainer link = csma.Install (NodeContainer (terminals.Get (i), csmaSwitch));
      terminalDevices.Add (link.Get (0));
      switchDevices.Add (link.Get (1));
    }

  // Create the bridge netdevice, which will do the packet switching
  Ptr<Node> switchNode = csmaSwitch.Get (0);
  BridgeHelper bridge;
  bridge.Install (switchNode, switchDevices);

  // Add internet stack to the terminals
  InternetStackHelper internet;
  internet.Install (terminals);

  // We've got the "hardware" in place.  Now we need to add IP addresses.
  //
  NS_LOG_INFO ("Assign IP Addresses.");
  Ipv4AddressHelper ipv4;
  ipv4.SetBase ("10.1.1.0", "255.255.255.0");
  ipv4.Assign (terminalDevices);

  //
  // Create an OnOff application to send UDP datagrams from node zero to node 1.
  //
  NS_LOG_INFO ("Create Applications.");
  uint16_t port = 9;   // Discard port (RFC 863)

  OnOffHelper onoff ("ns3::UdpSocketFactory", 
                     Address (InetSocketAddress (Ipv4Address ("10.1.1.2"), port)));
  //onoff.SetConstantRate (DataRate ("500kb/s"));
  onoff.SetAttribute ("OnTime", StringValue ("ns3::ConstantRandomVariable[Constant=1.0]"));
  onoff.SetAttribute ("OffTime", StringValue ("ns3::ConstantRandomVariable[Constant=1.0]"));
  onoff.SetAttribute ("DataRate", DataRateValue (5000000));

  ApplicationContainer app1 = onoff.Install (terminals.Get (0));
  // Start the application
  app1.Start (Seconds (1.0));
  app1.Stop (Seconds (10.0));

  // Create an optional packet sink to receive these packets
  PacketSinkHelper sink ("ns3::UdpSocketFactory",
                         Address (InetSocketAddress (Ipv4Address::GetAny (), port)));
  ApplicationContainer sinkApp1 = sink.Install (terminals.Get (1));
  sinkApp1.Start (Seconds (1.0));
  sinkApp1.Get(0)->TraceConnect("Rx", "Flow1", MakeCallback(&Rxtime));

  onoff.SetAttribute ("Remote", AddressValue (InetSocketAddress (Ipv4Address ("10.1.1.1"), port)));
  onoff.SetAttribute ("DataRate", DataRateValue (10000000));
  onoff.SetAttribute ("OnTime", StringValue ("ns3::ConstantRandomVariable[Constant=0.3]"));
  onoff.SetAttribute ("OffTime", StringValue ("ns3::ConstantRandomVariable[Constant=0.7]"));

  ApplicationContainer app2 = onoff.Install (terminals.Get(3));
  app2.Start (Seconds (3.0));
  app2.Stop (Seconds (13.0));

  ApplicationContainer sinkApp2 = sink.Install (terminals.Get (0));
  sinkApp2.Start (Seconds (3.0));
  sinkApp2.Get(0)->TraceConnect("Rx", "Flow2", MakeCallback(&Rxtime));

  csma.EnablePcapAll ("csma-bridge2", false);

  //
  // Now, do the actual simulation.
  //
  NS_LOG_INFO ("Run Simulation.");
  Simulator::Stop(Seconds (15));
  Simulator::Run ();
  Simulator::Destroy ();
  NS_LOG_INFO ("Done.");
}