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+# Network Simulation: Labwork 1
+Consider the ns-3 example `first.cc`.
+
+## Scenario
+Two P2P UDP/IPv4 nodes are simulated for a simple echo operation
+over the network 10.1.1.0 subnet mask 255.255.255.0
+of bandwidth 5 Mbps and latency 2 ms:
+
+```c++
+NodeContainer nodes;
+nodes.Create (2);
+
+PointToPointHelper pointToPoint;
+pointToPoint.SetDeviceAttribute ("DataRate", StringValue ("5Mbps"));
+pointToPoint.SetChannelAttribute ("Delay", StringValue ("2ms"));
+
+NetDeviceContainer devices;
+devices = pointToPoint.Install (nodes);
+
+Ipv4AddressHelper address;
+address.SetBase ("10.1.1.0", "255.255.255.0");
+
+Ipv4InterfaceContainer interfaces = address.Assign (devices);
+```
+
+## Protocols
+In the example, Internet Protocol version 4 and User Datagram Protocol
+are simulated.
+
+## Setup
+### Nodes
+There are two UDP nodes set up: a client and a server,
+whose addresses are automatically assigned:
+
+```c++
+Ipv4InterfaceContainer interfaces = address.Assign (devices);
+```
+
+#### Server
+The echo server is bound to port 9 and kept alive from second 1 to 10:
+
+```c++
+UdpEchoServerHelper echoServer (9);
+
+ApplicationContainer serverApps = echoServer.Install (nodes.Get (1));
+serverApps.Start (Seconds (1.0));
+serverApps.Stop (Seconds (10.0));
+```
+
+#### Client
+The echo client is created to communicate with the aforementioned server
+and stay alive from second 2 to 10:
+
+```c++
+UdpEchoClientHelper echoClient (interfaces.GetAddress (1), 9);
+
+ApplicationContainer clientApps = echoClient.Install (nodes.Get (0));
+clientApps.Start (Seconds (2.0));
+clientApps.Stop (Seconds (10.0));
+```
+
+### Traffic
+The echo client is configured to send one 1 KiB packet:
+
+```c++
+echoClient.SetAttribute ("MaxPackets", UintegerValue (1));
+echoClient.SetAttribute ("Interval", TimeValue (Seconds (1.0)));
+echoClient.SetAttribute ("PacketSize", UintegerValue (1024));
+```
+
+The interval between packets has no effect here since we only send one.
+
+The simulated traffic is logged as follows:
+
+```console
+$ waf --run first.cc
+At time +2s client sent 1024 bytes to 10.1.1.2 port 9
+At time +2.00369s server received 1024 bytes from 10.1.1.1 port 49153
+At time +2.00369s server sent 1024 bytes to 10.1.1.1 port 49153
+At time +2.00737s client received 1024 bytes from 10.1.1.2 port 9
+```
+
+It can be seen that the round-trip time (RTT) is 7.37 ms
+and delays in both direction are approximately equal (3.69 ms vs 3.68 ms)
+since both send and receive a 1 KiB packet over the same network configuration.
+Theoretically, the RTT can be computed as
+
+    RTT = 2 * (1 KiB / 5 Mbps + 2 ms)
+        = 2 * (1.6384 ms + 2 ms)
+        = 2 * 3.6384 ms
+        = 7.2768 ms
+
+The difference from the simulated figure might be explained
+through non-network delays, such as processing time.