Implementing a Routing Algorithm – Lab2 CSE514 – Computer Networking Pennsylvania State University Spring2009 Wei Zhong
[email protected]
1. Overvi Overvi ew 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 Figure1.
Figure 1: Network 1: Network topology and link costs for DV routing lab
2. Basic Basic Requi Requi rement The routines you will write: For the basic part of the assignment, you are to write the following routines which will ``execute'' asynchronously within the emulated environment that we have written for this assignment. For node 0, you will write the 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. 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 tolayer2(), 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 of 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, the distance table inside each node is the principal data structure used by the distance vector algorithm. You will find it convenient to declare the distance table as a 4-by-4 array of int's, where entry [i,j] in the distance table in node 0 is node 0's currently computed cost to node i via direct neighbor j. If 0 is not directly connected to j, you can ignore this entry. We will use the convention that the integer value 999 is ``infinity.''
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()
Figure 2: Relationship between procedures inside node 0
3. Implementation o f no de 0 We hereby simply introduce how the routines in node 0 are implemented. Other routines in node1, node2 and node3 are similar to those in node 0. •
Declare the constant and data structur e required by t he routine rtinit0() and rtu pdate0(). Neighbour[i] = 1 represents the node i is directly connected with the current node 0. Otherwise, node i is not connected with node 0 or node i is node 0 itself. The dtcost array stands for the cost between node 0 and its direct neighboring node and the value of this array won’t change forever. The dtvector0 array keeps track of the distance vector of node 0. The key word static ensures no file can use these variables outside this file. # define NODE 4
# define INFINITY 999 static int neighbour[NODE] = {0,1,1,1}; static int dtcost[NODE] = {0,1,3,7}; static int dtvector0[NODE] = {0,1,3,7}; •
Implementation o f rti nit0() Print out a message when rtinit0() is called: printf("rtinit0 is called at t=%.3f\n",clocktime);
Initialize the distance table, distance table of node 0 looks like this: 0 1 2 3
0 1 2 3 999 999 999 999 999 1 999 999 999 999 3 999 999 999 999 7
We simply ignore the first row and first column since it doesn’t help for reaching node 0 via other nodes or reaching other nodes via node 0 itself. for(i = 0; i < NODE; i++) for(j = 0; j < NODE; j++){ if( (neighbour[i] == 1)&&(i == j) ) dt0.costs[i][j] = dtcost[i]; else dt0.costs[i][j] = INFINITY; }
Traverse the neighbour array and send out the packet to its neighboring node. The packet mainly contains the source node, destination node and the distance vector of node 0. struct rtpkt temp; for(i = 0; i < NODE; i++) { if(neighbour[i] == 1){ temp.sourceid = 0; temp.destid = i; for(j = 0;j< NODE; j++){ temp.mincost[j] = dtvector0[j]; } tolayer2(temp); } } •
Implemenation of rtupd ate0() Print out a message once this routine is called and indicate the identity of the sender sending packet to this routine.
printf("rtupdate0 is called at t=%.3f. " ,clocktime); printf("node 0 is receiving packet from node %d\n" , rcvdpkt->sourceid);
As long as node 0 receives a packet from its direct neighboring node, it computes the cost to all the nodes except itself via this direct neighboring node, updating the distance table and distance vector of node 0 if a shorter path is found. for(i = 0; i < NODE; i++){ if(i != 0){ tempCost = dtcost[sourceid] + rcvdpkt->mincost[i]; if(tempCost < dt0.costs[i][sourceid]){ dt0.costs[i][sourceid] = tempCost; printf("Node 0's distance table updated.\n" ); printdt0(&dt0); } if(tempCost < dtvector0[i]){ vectorChange = 1; dtvector0[i] = tempCost; } } }
If the distance vector of node 0 is changed, send out its updated distance vector to all its direct neighboring nodes and print out a message advising that node 0 is sending out packet. if(vectorChange == 1){ struct rtpkt temp; for(i = 0; i < NODE; i++) { if(neighbour[i] == 1){ temp.sourceid = 0; temp.destid = i; for(j = 0;j< NODE; j++){ temp.mincost[j] = dtvector0[j]; } printf("Packet is being sent to node %d from Node 0.\n" ,i); tolayer2(temp); } } printf("\n"); }
4. Sample Output 1)
Put node0.c, node1.c, node2.c, node3.c and prog3.c under the same directory.
2)
Compile these files together by entering the following command.
3)
Execute the program by entering ‘a.out’ and indicate the TRACE value.
4)
Here comes the output:
……
