CNT4704: Analysis of Computer Communication Networks

Fall 2012

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Programming Assignment 3: Distributed Simulation of Distance Vector Routing protocol
(Assigned: Nov. 13th, Due: Nov. 29th midnight on WebCourse)

Overview

In this lab, you will be writing a "distributed" set of procedures that implement a distributed asynchronous distance vector routing for the network shown in Figure 1. This project is implemented in the similar way as in project 2---a simulator is provided (prog3.c) and your task is to complete the coding for several function calls that will be called by the simulator in a statistical way. To complete the project, you need to understand well the example shown on Page 32 in lecture notes Chapter4-part2.ppt. In addition, I introduced a similar example in lecture 25 (Nov. 13th class).

The routines you will write:

You are to write the following routines which will ``execute'' asynchronously within the emulated environment that the textbook authors have written for this assignment.

For node 0, you will write the following two routines:

• rtinit0() This routine will be called once at the beginning of the emulation. rtinit0() has no arguments. It should initialize the distance table in node 0 to reflect the direct costs of 1, 3, and 7 to nodes 1, 2, and 3, respectively. It should also initialize its linkCost0[] to all other nodes since this linkcost will be used in calculation all the time. In Figure 1, all links are bi-directional and the costs in both directions are identical. After initializing the distance table, and any other data structures needed by your node 0 routines, it should then send its directly-connected neighbors (in this case, 1, 2 and 3) the cost of it minimum cost paths to all other network nodes. This minimum cost information is sent to neighboring nodes in a routing packet by calling the routine sendrtp(), as described below. The format of the routing packet is also described below.

• rtupdate0(struct rtpkt *rcvdpkt). This routine will be called when node 0 receives a routing packet that was sent to it by one if its directly connected neighbors. The parameter *rcvdpkt is a pointer to the packet that was received.

rtupdate0() is the "heart" of the distance vector algorithm. The values it receives in a routing packet from some other node i contain i's current shortest path costs to all other network nodes. rtupdate0() uses these received values to update its own distance table (as specified by the distance vector algorithm). If its own minimum cost to another node changes as a result of the update, node 0 informs its directly connected neighbors of this change in minimum cost by sending them a routing packet. Recall that in the distance vector algorithm, only directly connected nodes will exchange routing packets. Thus nodes 1 and 2 will communicate with each other, but nodes 1 and 3 will not communicate with each other.

As we saw in class (example in Page 42 in Chapter4-part2.ppt, and the example introduced on Nov. 13th class), the distance table inside each node is the principal data structure used by the distance vector algorithm. It is declared as a 4-by-4 array of int's, where the i-th row is the distance vector of node i. If the node i is not directly connected to the current node, this i-th row entry can be ignored. We will use the convention that the integer value 99 is ``infinity'', which is defined as micro in all code files.

Figure. 2 provides a conceptual view of the relationship of the procedures inside node 0.

Similar routines are defined for nodes 1, 2 and 3. Thus, you will write 8 procedures in all: rtinit0(), rtinit1(), rtinit2(), rtinit3(),rtupdate0(), rtupdate1(), rtupdate2(), rtupdate3()

Software Interfaces

The procedures described above are the ones that you will write. The following routines have been provided in the simulator that can be called by your routines:

sendrtpkt(int srcid, int destid, int mincosts[])

       It will create a packet containing the distance vector mincosts[] (4 entries) and send to destination node destid (specifying that it is sent from the source node srcid). And at the same time print out information of such event. After a simulated time delay, the rtupdate?() function of the destination node destid will be called to process this received packet.

The packet is the following structure, which is already declared for you. 

extern struct rtpkt {
  int sourceid;  /* id of node sending this pkt, 0, 1, 2, or 3 */
  int destid;    /* id of router to which pkt being sent
                    (must be an immediate neighbor) */
  int mincost[4];    /* min cost to node 0 ... 3 */
  };

printdt0()

will pretty print the distance table saved on node 0. printdt0() and the structure declaration for the node 0 distance table are declared in the file node0.c. Similar pretty-print routines are defined for you in the files node1.c, node2.c node3.c for the other 3 nodes.

The Simulated Network Environment

Your procedures rtinit0(), rtinit1(), rtinit2(), rtinit3() and rtupdate0(), rtupdate1(), rtupdate2(), rtupdate3() send routing packets (whose format is described above) into the medium. The medium will deliver packets in-order, and without loss to the specified destination. Only directly-connected nodes can communicate. The delay between a sender and a receiver is statistically variable (and unknown).

When you compile your procedures and the provided prog3.c procedures together and run the resulting program, you will be asked to specify only one value regarding the simulated network environment:

• Tracing. Setting a tracing value of 1 or 2 will print out useful information about what is going on inside the emulation (e.g., what's happening to packets and timers). A tracing value of 0 will turn this off. A tracing value greater than 2 will display all sorts of odd messages that are for my own emulator-debugging purposes.

A tracing value of 2 may be helpful to you in debugging your code. You should keep in mind that real implementors do not have underlying networks that provide such nice information about what is going to happen to their packets!

The Required Content in Project Report

You are to write the procedures rtinit0(), rtinit1(), rtinit2(), rtinit3() and rtupdate0(), rtupdate1(), rtupdate2(), rtupdate3() which together will implement a distributed, asynchronous computation of the distance tables for the topology and costs shown in Figure 1.

You should put your procedures for nodes 0 through 3 in files called node0.c, .... node3.c. You are NOT allowed to declare any global variables that are visible outside of a given C file (e.g., any global variables you define in node0.c. may only be accessed inside node0.c). This is to force you to abide by the coding conventions that you would have to adopt is you were really running the procedures in four distinct nodes. To compile your routines use: cc -o dvSim prog3.c node0.c node1.c node2.c node3.c , which will generate the executable program called dvSim. Prototype versions of these files are here: node0.c, node1.c, node2.c, node3.c. Note that do not pay attention to the empty function linkhandler0(linkid, newcost) in the above 4 nodes' code files. It is used by the textbook authors for advanced graduate course teaching.

This assignment can be completed on any machine supporting C. It makes no use of UNIX features.

You are expected to submit in the four code file (code0.c ~ code3.c), and the generated executable code. And a design document with a sample output. You are not supposed to modify the simulator code prog3.c

For your sample output, your procedures should call printdt?() at the end of rtinit?(), and call printdt?() whenever your node needs to send out a distance vector update message in rtupdate?().

The sample output should be an output listing with a TRACE value of 2. Highlight the final distance table produced in each node. Your program will run until there are no more routing packets in-transit in the network, at which point the emulator will terminate.

JAVA Version Of This Assignment