Add week 4 materials

materials/04-group-comm/seminar/ip_multicast/sender/Dockerfile

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+FROM python:3.12-slim
+
+COPY . .
+
+CMD ["python", "-u" , "sender.py"]

materials/04-group-comm/seminar/ip_multicast/sender/sender.py

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+import socket
+import struct
+
+
+if __name__ == '__main__':
+    in_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    in_socket.bind(('', 9999))
+    out_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    out_socket.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, struct.pack('b', 1))
+    print("ready: listening on UDP :9999, forwarding to 224.0.2.0:10000", flush=True)
+    while True:
+        data, addr = in_socket.recvfrom(1024)
+        out_socket.sendto(data, ('224.0.2.0', 10000))
+        print(f'forwarded {data!r} from {addr} to 224.0.2.0:10000', flush=True)