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Tutorial : Multicast Chat System, Java Multicast Programming

Questions and Answers

1. Can you create a MulticastSocket that listens and transmits on a UDP port that has been used by a DatagramSocket sitting in the same machine?

No. The reason is that multicast and unicast all share the same set of UDP ports.

2. Is it possible to create a MulticastSocket that listens and transmits on a UDP port that has been used by other MulticastSocket sitting in the same machine?.

Yes, because multiple clients on the same machine can join in a multicast conversation.

3. List the seven methods that add to MulticastSocket on top of DatagramSocket.

They are joinGroup(), leaveGroup(), setTimeToLive(), getTimeToLive(), setInterface(), getInterface(), and send() with an option to specify the TTL for the packet.

4. Which types of exception may all the methods of MulticastSocket throw?

The methods of MulticasstSocket may throw exceptions of the type IOException.

5. In this peer-to-peer mode of a multicast chat system, can we prevent anyone from joining the multicast group? If so, how?

No. Most multicast senders are indiscriminate about who they talk to. Therefore, it’s easy to join a group, and watch the data that’s being sent to it.

6. Can we modify the program so that it is able to accept UDP packets only from the pre-specified range of IP addresses? If so, how?

No. You have to accept a whole UDP packet before you know who the sender is; you can choose to skip a particular packet by not displaying its contents, but you still have to receive the whole packet first.

7. If somebody in the network knows the multicast group and the UDP port number being used by the multicast chat system, is it possible for him or her to create annoying effects, or even crash our system?

Yes, it is possible.