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
- Collision detection
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.");
}
Software Engineer @ LG Electronics