怎么在ns-3里构建哑铃型拓扑？

在 ns-3 中构建哑铃型拓扑，需要使用网络拓扑构建器，并配置相应的网络参数。具体步骤如下：

1. 导入必要的头文件：

#include "ns3/core-module.h"
#include "ns3/network-module.h"
#include "ns3/internet-module.h"
#include "ns3/point-to-point-module.h"

2. 使用 `PointToPointHelper` 创建两个点对点的网络节点：

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

NodeContainer nodes;
nodes.Create (2);

NetDeviceContainer devices;
devices = pointToPoint.Install (nodes);

3. 在节点之间安装 Internet 协议栈：

InternetStackHelper stack;
stack.Install (nodes);

Ipv4AddressHelper address;
address.SetBase ("10.1.1.0", "255.255.255.0");

Ipv4InterfaceContainer interfaces = address.Assign (devices);

4. 设置应用程序，模拟数据流：

uint16_t sinkPort = 8080;
Address sinkAddress (InetSocketAddress (interfaces.GetAddress (1), sinkPort));
PacketSinkHelper packetSinkHelper ("ns3::TcpSocketFactory", InetSocketAddress (Ipv4Address::GetAny (), sinkPort));
ApplicationContainer sinkApps = packetSinkHelper.Install (nodes.Get (1));
sinkApps.Start (Seconds (0.));
sinkApps.Stop (Seconds (10.));

Ptr<Socket> ns3TcpSocket = Socket::CreateSocket (nodes.Get (0), TcpSocketFactory::GetTypeId ());

Ptr<MyApp> app = CreateObject<MyApp> ();
app->Setup (ns3TcpSocket, sinkAddress, 1040, 100, DataRate ("250Kbps"));
nodes.Get (0)->AddApplication (app);
app->SetStartTime (Seconds (1.));
app->SetStopTime (Seconds (10.));

5. 运行模拟：

Simulator::Run ();
Simulator::Destroy ();

以上代码仅作为示例，请根据