COSC 450: Computer Networks

Homework Assignment #3

Due: 3/31/2009

For the third homework assignment, you are to write a Java program to simulate a simplified OSPF router. Your program should be run simultaneously on three different machines in the lab to simulate three different routers. All of the routers are in the same area of the autonomous system. Use Figure 6.8 of the book for the network topology, except the router R2 is the area boundary router and the "Rest of the Internet" is the backbone of the AS. You may assume the following restrictions and simplifcations:

• The only links are stub and transient. There are no point-to-point or virtual links.
• Each router initially knows only to which networks it is directly connected. Take this information from Figure 6.8 of the book. When the program begins running it will read from a file the information about which networks it is directly connnected to and through which interfaces.
• The only packets used will be Hello and Link state updates. Your code does not need to implement Database description, Link state request, or Link state acknowledgement packets. The router's graph will be incrementally built from the Link state update packets. We will assume that that no packets are dropped or corrupted, so there will be no need for Link state acknowledgement packets. The stub networks and the backbone network will be simulated (see below). The Ethernet in the lab will substitute for network 111.0.0.0 in the diagram.
• The Hello packets will be broadcast and a router will respond directly to its neighbor with Link state updates upon receipt of a Hello packet.
• The only LSA types are Router Link LSAs and Network Links LSAs.
• A transient network should have a designated router, but not a backup designated router.
• There is only one Type of Service (TOS) and hence only one metric. You may set the values of the metric to whatever values you choose.
• LSAs will expire after 2 minutes and will be re-sent every 30 seconds.
• The dead interval in the Hello message should be set to 3 minutes.
• The packets will be sent using UDP instead of IP.
• All the routers should use the same UDP port number for communications. The number of that port should be calculated as follows: 10000 + your two initials as capital letters in ASCII code represented by two digits each. For example, my port number would be D (ASCII 68) S (ASCII 83) -> 16883.

Your program should read its network information from a file (which will be different for each router) and generate an initial graph and routing table. The program will then send out a Hello message. Upon receipt of a Hello message, your router will share its information with a neighboring router using Link State update packets. As it receives Link State update packets, it will propagate them to the other routers and also update its graph and routing table. The link state information should expire in the given interval unless refreshed and the graph and table should be changed accordingly.

In addition, the router should randomly simulate changes in connectivity for the networks to which it is connected and to itself. That is, at random times, network connections should drop or go back up, and the router should incorporate the appropriate changes. Periodically, the router itself should go down. That change should be noted by the neighboring routers (after the dead interval). Simulate a router going down by having your program sleep for a period of time, rather than ending the program. When the router goes back up, remember to send out a new Hello message.

There is no need to simulate network traffic - just simulate network events such as links and routers going down and back up.

Each time an event happens that changes a router's table, your program should print out that event and print out the new table.