在上一節中，我們模擬了一個匯流排型網路，這一節嘗試將上一節中的n0變成一個無線的AP，再連上幾個節點。這也是NS3中的示例third.cc乾的事情，只是我們用Python實現。

// Default Network Topology
//
//   Wifi 10.1.3.0
//                 AP
//  *    *    *    *
//  |    |    |    |    10.1.1.0
// n5   n6   n7   n0 -------------- n1   n2   n3   n4
//                   point-to-point  |    |    |    |
//                                   ================
//                                     LAN 10.1.2.0
 

與上一節一樣，先構造p2p網路，再構建匯流排型網線：

# 構建點對點連線
p2pNodes = ns.network.NodeContainer()
p2pNodes.Create (2)

pointToPoint = ns.point_to_point.PointToPointHelper()
pointToPoint.SetDeviceAttribute ("DataRate", ns.core.StringValue ("5Mbps"))
pointToPoint.SetChannelAttribute ("Delay", ns.core.StringValue ("2ms"))
p2pDevices = pointToPoint.Install (p2pNodes)

# 構建匯流排連線
nCsma = 3

csmaNodes = ns.network.NodeContainer()
csmaNodes.Add (p2pNodes.Get (1))
csmaNodes.Create (nCsma)

csma = ns.csma.CsmaHelper()
csma.SetChannelAttribute ("DataRate", ns.core.StringValue ("100Mbps"))
csma.SetChannelAttribute ("Delay", ns.core.TimeValue (ns.core.NanoSeconds (6560)))
csmaDevices = csma.Install (csmaNodes)
 

接著構建無線網路：

# 構建Wifi連線
nWifi = 3
wifiStaNodes = ns.network.NodeContainer()
wifiStaNodes.Create (nWifi)
wifiApNode = p2pNodes.Get (0)

channel = ns.wifi.YansWifiChannelHelper.Default ()
phy = ns.wifi.YansWifiPhyHelper.Default ()
phy.SetChannel (channel.Create ())

接著配置AP：

# 配置AP
wifi = ns.wifi.WifiHelper.Default ()
wifi.SetRemoteStationManager ("ns3::AarfWifiManager")

mac = ns.wifi.NqosWifiMacHelper.Default ()

ssid = ns.wifi.Ssid ("ns-3-ssid")
mac.SetType ("ns3::StaWifiMac",
            "Ssid", ns.wifi.SsidValue (ssid),
            "ActiveProbing", ns.core.BooleanValue (False))

staDevices = wifi.Install (phy, mac, wifiStaNodes)

mac.SetType ("ns3::ApWifiMac",
            "Ssid", ns.wifi.SsidValue (ssid))

apDevices = wifi.Install (phy, mac, wifiApNode);

 

接著配置無線節點的位置引數：

# 配置無線節點的位置
mobility = ns.mobility.MobilityHelper()

mobility.SetPositionAllocator ("ns3::GridPositionAllocator",
                                "MinX", ns.core.DoubleValue (0.0),
                                "MinY", ns.core.DoubleValue (0.0),
                                "DeltaX", ns.core.DoubleValue (5.0),
                                "DeltaY", ns.core.DoubleValue (10.0),
                                "GridWidth", ns.core.UintegerValue (3),
                                "LayoutType", ns.core.StringValue ("RowFirst"))

mobility.SetMobilityModel ("ns3::RandomWalk2dMobilityModel",
                            "Bounds", ns.mobility.RectangleValue (ns.mobility.Rectangle (-50, 50, -50, 50)))
mobility.Install (wifiStaNodes)

mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel")
mobility.Install (wifiApNode)

接著安裝協議棧：

# 安裝協議棧
stack = ns.internet.InternetStackHelper()
stack.Install (csmaNodes)
stack.Install (wifiApNode)
stack.Install (wifiStaNodes)

配置IP，這個和上一節一樣，只是加上10.1.3.0網段而已：

# 配置IP
address = ns.internet.Ipv4AddressHelper()
address.SetBase (
    ns.network.Ipv4Address("10.1.1.0"), 
    ns.network.Ipv4Mask("255.255.255.0"))
p2pInterfaces = address.Assign (p2pDevices)

address.SetBase (
    ns.network.Ipv4Address("10.1.2.0"), 
    ns.network.Ipv4Mask("255.255.255.0"))
csmaInterfaces = address.Assign (csmaDevices)

address.SetBase (
    ns.network.Ipv4Address("10.1.3.0"), 
    ns.network.Ipv4Mask("255.255.255.0"))
address.Assign (staDevices)
address.Assign (apDevices)

接下來模擬一個Echo服務，這個與上一節相同，只是Client安裝在了Wifi節點上。

# 配置應用程式
echoServer = ns.applications.UdpEchoServerHelper (9)

serverApps = echoServer.Install (csmaNodes.Get (nCsma))
serverApps.Start (ns.core.Seconds (1.0))
serverApps.Stop (ns.core.Seconds (20.0))

echoClient = ns.applications.UdpEchoClientHelper (csmaInterfaces.GetAddress (nCsma), 9)
echoClient.SetAttribute ("MaxPackets", ns.core.UintegerValue (5))
echoClient.SetAttribute ("Interval", ns.core.TimeValue (ns.core.Seconds (1.0)))
echoClient.SetAttribute ("PacketSize", ns.core.UintegerValue (1024))

clientApps = echoClient.Install (wifiStaNodes.Get (nWifi - 1))
clientApps.Start (ns.core.Seconds (2.0))
clientApps.Stop (ns.core.Seconds (20.0))

接下來的部分與上一節幾乎完全相同，只是加上了Simulator.Stop，因為如果沒有這個函式呼叫，那麼將導致Simulator.Run永遠不會停止：

# 全域性路由管理器根據節點產生 的鏈路通告為每個節點建立路由表
ns.internet.Ipv4GlobalRoutingHelper.PopulateRoutingTables()

ns.core.Simulator.Stop (ns.core.Seconds (10.0));

pointToPoint.EnablePcapAll ("third");
csma.EnablePcap ("third", csmaDevices.Get (1), True)
phy.EnablePcap ("third", apDevices.Get (0))

anim = ns.netanim.AnimationInterface('third.xml')
anim.SetConstantPosition(p2pNodes.Get(0), 10, 10)
anim.SetConstantPosition(csmaNodes.Get(0), 30, 10)
anim.SetConstantPosition(csmaNodes.Get(1), 40, 10)
anim.SetConstantPosition(csmaNodes.Get(2), 50, 10)
anim.SetConstantPosition(csmaNodes.Get(3), 60, 10)
anim.EnablePacketMetadata(True)

# 開始模擬
ns.core.Simulator.Run()
ns.core.Simulator.Destroy()

看看NetAnim顯示的模擬結果：

再看看third-0-1.pcap的內容：

如我們所願，802.11協議，呵呵~~~~~