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# Network Simulation: Labwork 4
The code presented in this report is a heavily modified version of the ns-3
tutorial `third`.
## Wireless Network Topology
Consider a Wi-Fi network topology of 3 nodes (1 access point AP and 2 stations
STA1 and STA2) using wireless channel. The AP is connected to an echo server S
via LAN channel:
```c++
NodeContainer p2pNodes;
p2pNodes.Create (2); // AP and S
NodeContainer wifiApNode = p2pNodes.Get (0);
PointToPointHelper pointToPoint; // LAN channel
pointToPoint.SetDeviceAttribute ("DataRate", StringValue ("5Mbps"));
pointToPoint.SetChannelAttribute ("Delay", StringValue ("2ms"));
NetDeviceContainer p2pDevices = pointToPoint.Install (p2pNodes);
NodeContainer wifiStaNodes;
wifiStaNodes.Create (2); // STA 1 and STA2
YansWifiChannelHelper channel = YansWifiChannelHelper::Default ();
YansWifiPhyHelper phy = YansWifiPhyHelper::Default ();
phy.SetChannel (channel.Create ());
WifiHelper wifi;
wifi.SetRemoteStationManager ("ns3::AarfWifiManager");
WifiMacHelper mac;
Ssid ssid = Ssid ("ns-3-ssid");
mac.SetType ("ns3::StaWifiMac",
"Ssid", SsidValue (ssid),
"ActiveProbing", BooleanValue (false));
NetDeviceContainer staDevices = wifi.Install (phy, mac, wifiStaNodes);
mac.SetType ("ns3::ApWifiMac", "Ssid", SsidValue (ssid));
NetDeviceContainer apDevices = wifi.Install (phy, mac, wifiApNode);
MobilityHelper mobility;
mobility.SetPositionAllocator ("ns3::GridPositionAllocator",
"MinX", DoubleValue (0.0),
"MinY", DoubleValue (0.0),
"DeltaX", DoubleValue (5.0),
"DeltaY", DoubleValue (10.0),
"GridWidth", UintegerValue (3),
"LayoutType", StringValue ("RowFirst"));
mobility.SetMobilityModel ("ns3::ConstantPositionMobilityModel");
mobility.Install (wifiStaNodes);
mobility.Install (wifiApNode);
```
## Echo Server
Implement scenario of STA1 is a client that sends 100 packets within 10 s to S.
```c++
InternetStackHelper stack;
stack.Install (p2pNodes);
stack.Install (wifiStaNodes);
Ipv4AddressHelper address;
address.SetBase ("10.1.2.0", "255.255.255.0");
Ipv4InterfaceContainer p2pInterfaces;
p2pInterfaces = address.Assign (p2pDevices);
address.SetBase ("10.1.1.0", "255.255.255.0");
address.Assign (staDevices);
address.Assign (apDevices);
UdpEchoServerHelper echoServer (9);
ApplicationContainer serverApps = echoServer.Install (p2pNodes.Get (1));
serverApps.Start (Seconds (1.0));
serverApps.Stop (Seconds (12.0));
UdpEchoClientHelper echoClient (p2pInterfaces.GetAddress (1), 9);
echoClient.SetAttribute ("MaxPackets", UintegerValue (100));
echoClient.SetAttribute ("Interval", TimeValue (MilliSeconds (100)));
echoClient.SetAttribute ("PacketSize", UintegerValue (1024));
ApplicationContainer clientApps = echoClient.Install (wifiStaNodes.Get (0));
clientApps.Start (Seconds (2.0));
clientApps.Stop (Seconds (12.0));
Ipv4GlobalRoutingHelper::PopulateRoutingTables ();
Simulator::Stop (Seconds (12.0));
```
Capture the pcap trace from the access point, where all traffic in our setup
has to go through, and run the simulation:
```c++
phy.EnablePcap ("third", apDevices.Get (0));
```
The TCP dumped trace is attached as `third-0-1-station`. There is not much
to be deduced from it other than that the latency across Wi-Fi is now in
the order of milliseconds, i.e. tens of times worse than on a typical
Ethernet configuration. As expected, there is not any drop due to queuing
since we set the interval to 100 ms.
In addition, there is Beacon frames (which if I understand correctly
is to discover devices and keep updated about their stati). By default
they are 100 time units or 102.4 ms a part, which explains how the packet
delivery seems to alternate with the Beacon and Acknowledgement frames.
## Mobile Stations
Let the two STAs move in a random direction and speed respecting
to RandomWalk mode:
```c++
mobility.SetMobilityModel ("ns3::RandomWalk2dMobilityModel", "Bounds",
RectangleValue (Rectangle (-50, 50, -50, 50)));
mobility.Install (wifiStaNodes);
```
The TCP dumped trace is attached as `third-0-1-mobile`. To my surprise,
there exists only minor differences in delay of the first few packets,
and the mobile model actually has lower latency:
```diff
--- third-0-1-station 2021-03-24 22:50:45.137239064 +0700
+++ third-0-1-mobile 2021-03-24 22:46:33.867879542 +0700
@@ -25,18 +25,18 @@
1.728436 Beacon (ns-3-ssid) [6.0* 9.0 12.0* 18.0 24.0* 36.0 48.0 54.0 Mbit] ESS
1.830836 Beacon (ns-3-ssid) [6.0* 9.0 12.0* 18.0 24.0* 36.0 48.0 54.0 Mbit] ESS
1.933236 Beacon (ns-3-ssid) [6.0* 9.0 12.0* 18.0 24.0* 36.0 48.0 54.0 Mbit] ESS
-2.006146 ARP, Request who-has 10.1.1.3 (ff:ff:ff:ff:ff:ff) tell 10.1.1.1, length 32
-2.006162 Acknowledgment RA:00:00:00:00:00:03
-2.006240 ARP, Request who-has 10.1.1.3 (ff:ff:ff:ff:ff:ff) tell 10.1.1.1, length 32
-2.006449 ARP, Reply 10.1.1.3 is-at 00:00:00:00:00:05, length 32
-2.006621 Acknowledgment RA:00:00:00:00:00:05
-2.008131 IP 10.1.1.1.49153 > 10.1.2.2.9: UDP, length 1024
-2.008147 Acknowledgment RA:00:00:00:00:00:03
-2.021537 ARP, Request who-has 10.1.1.1 (ff:ff:ff:ff:ff:ff) tell 10.1.1.3, length 32
-2.021795 ARP, Reply 10.1.1.1 is-at 00:00:00:00:00:03, length 32
-2.021811 Acknowledgment RA:00:00:00:00:00:03
-2.021961 IP 10.1.2.2.9 > 10.1.1.1.49153: UDP, length 1024
-2.023498 Acknowledgment RA:00:00:00:00:00:05
+2.002146 ARP, Request who-has 10.1.1.3 (ff:ff:ff:ff:ff:ff) tell 10.1.1.1, length 32
+2.002162 Acknowledgment RA:00:00:00:00:00:03
+2.002240 ARP, Request who-has 10.1.1.3 (ff:ff:ff:ff:ff:ff) tell 10.1.1.1, length 32
+2.002449 ARP, Reply 10.1.1.3 is-at 00:00:00:00:00:05, length 32
+2.002621 Acknowledgment RA:00:00:00:00:00:05
+2.004131 IP 10.1.1.1.49153 > 10.1.2.2.9: UDP, length 1024
+2.004147 Acknowledgment RA:00:00:00:00:00:03
+2.014537 ARP, Request who-has 10.1.1.1 (ff:ff:ff:ff:ff:ff) tell 10.1.1.3, length 32
+2.014795 ARP, Reply 10.1.1.1 is-at 00:00:00:00:00:03, length 32
+2.014811 Acknowledgment RA:00:00:00:00:00:03
+2.014961 IP 10.1.2.2.9 > 10.1.1.1.49153: UDP, length 1024
+2.016498 Acknowledgment RA:00:00:00:00:00:05
2.035636 Beacon (ns-3-ssid) [6.0* 9.0 12.0* 18.0 24.0* 36.0 48.0 54.0 Mbit] ESS
2.101510 IP 10.1.1.1.49153 > 10.1.2.2.9: UDP, length 1024
2.101526 Acknowledgment RA:00:00:00:00:00:03
```
|
