4. 仿真流程 - ns3 | jluyeyu = blog

# 4. 仿真流程

在本节中，将介绍 ns3 中仿真的流程，

# 基本流程

使用 ns3 仿真时，一般经过以下 4 个步骤。

# 1. 选择或开发相应的模块

根据实际仿真对象和仿真场景选择相应的仿真模块：如有线网或还是无线网 ( Wi-Fi )，节点移动性 mobility ，能量 energy , 路由协议，应用程序 application 等，若是没有相应模块，那就需要自己编写 (在后续章节中讲述)。

# 2. 编写网络仿真脚本

若是有了相应的模块，那么我们就可以搭建网络仿真环境，ns-3 仿真脚本支持 2 种语言：C 和 Python，两种语言接口的 API 接口是一样的，但是部分 API 可能没有 Python 的接口。所以，仿真主要还是采用 C 进行编写。

编写 ns-3 仿真脚本的大体过程如下【具体的例子查看 examples/tutorial/ 下面的示例，后面也会分析一些】：

生成节点：ns-3 中节点相当于一个空的计算机外壳，我们需要根据需求给这个计算机安装网络所需要的软硬件，如网卡、应用程序、协议栈等。
安装网卡设备：不同的网络类型有不同的网络设备，从而提供不同的通信、物理层和 MAC 层，如 CSMA WI-FI WIMAX 和 point-to-point 等。
安装协议栈： ns-3 网络中一般是 TCP/IP 协议栈，依据网络选择具体协议，如是 UDP 还是 TCP ，选择何种不同的路由协议（ OLSR AODV 和 Global 等）并为其配置相应的 IP 地址， ns3 既支持 IPv4 也支持 IPv6 。
安装应用层协议：依据选择的传输层协议选择相应的应用层协议，但是有时需要自己编写应用层产生数据流量的代码。
其他配置：如节点是否移动，是否需要能量管理等
启动仿真：整个网络场景配置完毕，启动仿真

# 3. 仿真结果分析

仿真结果一般有两种：一种是网络场景，二是网络数据。网络场景如节点拓扑结构、移动模型等，一般通过可视化界面（ PyViz 或者 NetAnim ）可直接观测到。网络数据可以在可视化界面进行简单统计，此外还可以通过专门的统计框架 status 或者自行通过 ns3 提供的追踪框架收集、统计和分析相应的网络数据，如数据分组的延迟、网络流量、分组丢失和节点消息缓存队列的等， 但是上述统计结果对于一些新的开源模块可能不一定有用，所以更推荐的是采用 track 自行分析。。

# 4. 依据仿真结果调整网络配置参数或者修改源代码。

# 例子

为了更好的展示上述流程，样例代码是 aodv 的实例代码，位于 ns-3.xx/src/aodv/examples

完整代码如下所示：

	#include <iostream>
	#include <cmath>
	#include "ns3/aodv-module.h"
	#include "ns3/core-module.h"
	#include "ns3/network-module.h"
	#include "ns3/internet-module.h"
	#include "ns3/mobility-module.h"
	#include "ns3/point-to-point-module.h"
	#include "ns3/v4ping-helper.h"
	#include "ns3/yans-wifi-helper.h"

	using namespace ns3;

	/**
	* \ingroup aodv-examples
	* \ingroup examples
	* \brief Test script.
	*
	* This script creates 1-dimensional grid topology and then ping last node from the first one:
	*
	* [10.0.0.1] <-- step --> [10.0.0.2] <-- step --> [10.0.0.3] <-- step --> [10.0.0.4]
	*
	* ping 10.0.0.4
	*
	* When 1/3 of simulation time has elapsed, one of the nodes is moved out of
	* range, thereby breaking the topology. By default, this will result in
	* only 34 of 100 pings being received. If the step size is reduced
	* to cover the gap, then all pings can be received.
	*/
	class AodvExample
	{
	public:
	AodvExample ();
	/**
	* \brief Configure script parameters
	* \param argc is the command line argument count
	* \param argv is the command line arguments
	* \return true on successful configuration
	*/
	bool Configure (int argc, char **argv);
	/// Run simulation
	void Run ();
	/**
	* Report results
	* \param os the output stream
	*/
	void Report (std::ostream & os);

	private:

	// parameters
	/// Number of nodes
	uint32_t size;
	/// Distance between nodes, meters
	double step;
	/// Simulation time, seconds
	double totalTime;
	/// Write per-device PCAP traces if true
	bool pcap;
	/// Print routes if true
	bool printRoutes;

	// network
	/// nodes used in the example
	NodeContainer nodes;
	/// devices used in the example
	NetDeviceContainer devices;
	/// interfaces used in the example
	Ipv4InterfaceContainer interfaces;

	private:
	/// Create the nodes
	void CreateNodes ();
	/// Create the devices
	void CreateDevices ();
	/// Create the network
	void InstallInternetStack ();
	/// Create the simulation applications
	void InstallApplications ();
	};

	int main (int argc, char **argv)
	{
	AodvExample test;
	if (!test.Configure (argc, argv))
	NS_FATAL_ERROR ("Configuration failed. Aborted.");

	test.Run ();
	test.Report (std::cout);
	return 0;
	}

	//-----------------------------------------------------------------------------
	AodvExample::AodvExample () :
	size (10),
	step (50),
	totalTime (100),
	pcap (true),
	printRoutes (true)
	{
	}

	bool
	AodvExample::Configure (int argc, char **argv)
	{
	// Enable AODV logs by default. Comment this if too noisy
	// LogComponentEnable("AodvRoutingProtocol", LOG_LEVEL_ALL);

	SeedManager::SetSeed (12345);
	CommandLine cmd (__FILE__);

	cmd.AddValue ("pcap", "Write PCAP traces.", pcap);
	cmd.AddValue ("printRoutes", "Print routing table dumps.", printRoutes);
	cmd.AddValue ("size", "Number of nodes.", size);
	cmd.AddValue ("time", "Simulation time, s.", totalTime);
	cmd.AddValue ("step", "Grid step, m", step);

	cmd.Parse (argc, argv);
	return true;
	}

	void
	AodvExample::Run ()
	{
	// Config::SetDefault ("ns3::WifiRemoteStationManager::RtsCtsThreshold", UintegerValue (1)); // enable rts cts all the time.
	CreateNodes ();
	CreateDevices ();
	InstallInternetStack ();
	InstallApplications ();

	std::cout << "Starting simulation for " << totalTime << " s ...\n";

	Simulator::Stop (Seconds (totalTime));
	Simulator::Run ();
	Simulator::Destroy ();
	}

	void
	AodvExample::Report (std::ostream &)
	{
	}

	void
	AodvExample::CreateNodes ()
	{
	std::cout << "Creating " << (unsigned)size << " nodes " << step << " m apart.\n";
	nodes.Create (size);
	// Name nodes
	for (uint32_t i = 0; i < size; ++i)
	{
	std::ostringstream os;
	os << "node-" << i;
	Names::Add (os.str (), nodes.Get (i));
	}
	// Create static grid
	MobilityHelper mobility;
	mobility.SetPositionAllocator ("ns3::GridPositionAllocator",
	"MinX", DoubleValue (0.0),
	"MinY", DoubleValue (0.0),
	"DeltaX", DoubleValue (step),
	"DeltaY", DoubleValue (0),
	"GridWidth", UintegerValue (size),
	"LayoutType", StringValue ("RowFirst"));
	mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel");
	mobility.Install (nodes);
	}

	void
	AodvExample::CreateDevices ()
	{
	WifiMacHelper wifiMac;
	wifiMac.SetType ("ns3::AdhocWifiMac");
	YansWifiPhyHelper wifiPhy = YansWifiPhyHelper::Default ();
	YansWifiChannelHelper wifiChannel = YansWifiChannelHelper::Default ();
	wifiPhy.SetChannel (wifiChannel.Create ());
	WifiHelper wifi;
	wifi.SetRemoteStationManager ("ns3::ConstantRateWifiManager", "DataMode", StringValue ("OfdmRate6Mbps"), "RtsCtsThreshold", UintegerValue (0));
	devices = wifi.Install (wifiPhy, wifiMac, nodes);

	if (pcap)
	{
	wifiPhy.EnablePcapAll (std::string ("aodv"));
	}
	}

	void
	AodvExample::InstallInternetStack ()
	{
	AodvHelper aodv;
	// you can configure AODV attributes here using aodv.Set(name, value)
	InternetStackHelper stack;
	stack.SetRoutingHelper (aodv); // has effect on the next Install ()
	stack.Install (nodes);
	Ipv4AddressHelper address;
	address.SetBase ("10.0.0.0", "255.0.0.0");
	interfaces = address.Assign (devices);

	if (printRoutes)
	{
	Ptr<OutputStreamWrapper> routingStream = Create<OutputStreamWrapper> ("aodv.routes", std::ios::out);
	aodv.PrintRoutingTableAllAt (Seconds (8), routingStream);
	}
	}

	void
	AodvExample::InstallApplications ()
	{
	V4PingHelper ping (interfaces.GetAddress (size - 1));
	ping.SetAttribute ("Verbose", BooleanValue (true));

	ApplicationContainer p = ping.Install (nodes.Get (0));
	p.Start (Seconds (0));
	p.Stop (Seconds (totalTime) - Seconds (0.001));

	// move node away
	Ptr<Node> node = nodes.Get (size/2);
	Ptr<MobilityModel> mob = node->GetObject<MobilityModel> ();
	Simulator::Schedule (Seconds (totalTime/3), &MobilityModel::SetPosition, mob, Vector (1e5, 1e5, 1e5));
	}

从上述代码 run 函数中也可以很清晰的看出，实际上总共就分为几个步骤.

	void AodvExample::Run ()
	{
	CreateNodes (); // 创建节点
	CreateDevices ();// 创建设备
	InstallInternetStack ();// 安装协议栈
	InstallApplications ();// 设置应用

	std::cout << "Starting simulation for " << totalTime << " s ...\n";

	Simulator::Stop (Seconds (totalTime));
	Simulator::Run ();
	Simulator::Destroy ();
	}

# 1. 创建节点过程

创建了 size 个节点，并编号命名，

然后节点采用了 Grid 布局，(0,0) 点开始，

然后设置节点静止不动。

	void AodvExample::CreateNodes ()
	{
	std::cout << "Creating " << (unsigned)size << " nodes " << step << " m apart.\n";
	nodes.Create (size);
	// Name nodes
	for (uint32_t i = 0; i < size; ++i)
	{
	std::ostringstream os;
	os << "node-" << i;
	Names::Add (os.str (), nodes.Get (i));
	}
	// Create static grid
	MobilityHelper mobility;
	mobility.SetPositionAllocator ("ns3::GridPositionAllocator",
	"MinX", DoubleValue (0.0),
	"MinY", DoubleValue (0.0),
	"DeltaX", DoubleValue (step),
	"DeltaY", DoubleValue (0),
	"GridWidth", UintegerValue (size),
	"LayoutType", StringValue ("RowFirst"));
	mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel");
	mobility.Install (nodes);
	}

# 2. 创建设备

设置了 wifi 信道，wifi 的速率，pcap 设置一般没什么用，需要第三方软件分析可以采用。

	void AodvExample::CreateDevices ()
	{
	WifiMacHelper wifiMac;
	wifiMac.SetType ("ns3::AdhocWifiMac");
	YansWifiPhyHelper wifiPhy = YansWifiPhyHelper::Default ();
	YansWifiChannelHelper wifiChannel = YansWifiChannelHelper::Default ();
	wifiPhy.SetChannel (wifiChannel.Create ());
	WifiHelper wifi;
	wifi.SetRemoteStationManager ("ns3::ConstantRateWifiManager", "DataMode", StringValue ("OfdmRate6Mbps"), "RtsCtsThreshold", UintegerValue (0));
	devices = wifi.Install (wifiPhy, wifiMac, nodes);

	if (pcap)
	{
	wifiPhy.EnablePcapAll (std::string ("aodv"));
	}
	}

# 3. 安装协议栈

路由选择了 aodv 路由协议，设置了节点的 Ipv4 地址，设置是否需要打印路由表。

	void AodvExample::InstallInternetStack ()
	{
	AodvHelper aodv;
	// you can configure AODV attributes here using aodv.Set(name, value)
	InternetStackHelper stack;
	stack.SetRoutingHelper (aodv); // has effect on the next Install ()
	stack.Install (nodes);
	Ipv4AddressHelper address;
	address.SetBase ("10.0.0.0", "255.0.0.0");
	interfaces = address.Assign (devices);

	if (printRoutes)
	{
	Ptr<OutputStreamWrapper> routingStream = Create<OutputStreamWrapper> ("aodv.routes", std::ios::out);
	aodv.PrintRoutingTableAllAt (Seconds (8), routingStream);
	}
	}

# 4. 设置应用

设置了 ping 的应用程序，正常测网络性能，用的是 OnOffHelper 或者直接 socket 测试。

	void AodvExample::InstallApplications ()
	{
	V4PingHelper ping (interfaces.GetAddress (size - 1));
	ping.SetAttribute ("Verbose", BooleanValue (true));

	ApplicationContainer p = ping.Install (nodes.Get (0));
	p.Start (Seconds (0));
	p.Stop (Seconds (totalTime) - Seconds (0.001));

	// move node away
	Ptr<Node> node = nodes.Get (size/2);
	Ptr<MobilityModel> mob = node->GetObject<MobilityModel> ();
	Simulator::Schedule (Seconds (totalTime/3), &MobilityModel::SetPosition, mob, Vector (1e5, 1e5, 1e5));
	}

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