By B.A.Khivsara Assistant Professor Department of Computer Enginnering SNJB s KBJ COE,Chandwad

Transcription

1 By B.A.Khivsara Assistant Professor Department of Computer Enginnering SNJB s KBJ COE,Chandwad

2 Introduction to Routing Algorithms Distance Vector Routing Basics Program in C++ : Network Layer a -

3 Routers forward IP datagrams from one router to another on the path from source towards destination Routing protocols To decide on routes to be taken Routers must have idea of topology of internet in order to pick best route to take Decisions based on some least cost criteria May depend on the current conditions

4 One routing table is needed for each router One entry for each destination network Each entry shows next node on the route to destination

5 Routing Algorithms Static Routing Dynamic Routing routes manually defined change slowly over time or only one possible route Routes learned by communicating with other routers routes change more quickly

6 Path-selection model Destination-based Load-insensitive (e.g., static link weights) Minimum hop count or sum of link weights 5 6

7 Compute: path costs to all nodes From a given source u to all other nodes Cost of the path through each outgoing link Next hop along the least-cost path to s u 5 6 s 7

8 Define distances at each node x d x (y) = cost of least-cost path from x to y Update distances based on neighbors d x (y) = min {c(x,v) + d v (y)} over all u 8 neighbors v v w x 5 s y t z d u (z) = min{c(u,v) + d v (z), c(u,w) + d w (z)}

9 Introduction to Routing Algorithms Distance Vector Routing Basics Program in C++ : Network Layer a -9

10 c(x,v) = cost for direct link from x to v D x (y) = estimate of least cost from x to y Node x maintains its neighbors distance vectors For each neighbor v, x maintains D v = [D v (y): y є N ] Each node v periodically sends D v to its neighbors And neighbors update their own distance vectors D x (y) min v {c(x,v) + D v (y)} 0

11 Optimum -hop paths Table for A Table for B E C A 0 A B B C D E E F 6 F A A B 0 B C D D E F F A 6 F B D Table for C Table for D Table for E Table for F A A A A A 6 A B B B B B B C 0 C C C C C C D D D 0 D D D E E E 0 E E E F F F F F F 0 F

12 Optimum -hop paths Table for A Table for B E C A 0 A B B C 7 F D 7 B E E F 5 E A A B 0 B C F D D E F F F A 6 F B D Table for C Table for D Table for E Table for F A 7 F A 7 B A A A 5 B B F B B B F B B C 0 C C C C F C C D D D 0 D D D C E F E E 0 E E E F F F C F F F 0 F

13 Optimum -hop paths Table for A Table for B E C A 0 A B B C 6 E D 7 B E E F 5 E A A B 0 B C F D D E F F F A 6 F B D Table for C Table for D Table for E Table for F A 6 F A 7 B A A A 5 B B F B B B F B B C 0 C C C C F C C D D D 0 D D 5 F D C E F E 5 C E 0 E E E F F F C F F F 0 F

14 Distance vector protocol Nodes send distance vectors every 0 seconds or when an update causes a change in routing Link costs in RIP All links have cost Valid distances of through 5

15 Message complexity LS: with n nodes, E links, O(nE) messages sent DV: exchange between neighbors only Speed of Convergence LS: relatively fast DV: convergence time varies May be routing loops Count-to-infinity problem Robustness: what happens if router malfunctions? LS: Node can advertise incorrect link cost Each node computes only its own table DV: DV node can advertise incorrect path cost Each node s table used by others (error propagates) 5

16 Introduction to Routing Algorithms Distance Vector Routing Basics Program in C++ : Network Layer a - 6

17 #include<iostream> struct node { unsigned dist[6]; unsigned from[6]; }DVR[0]; int main() { cout<<"\n\n PROGRAM TO IMPLEMENT DISTANCE VECTOR ROUTING ALGORITHM "; int costmat[6][6]; int nodes, i, j, k;

18 cout<<"\n\n Enter the number of nodes : "; cin>>nodes; //Enter the nodes cout<<"\n Enter the cost matrix : \n" ; for(i = 0; i < nodes; i++) { for(j = 0; j < nodes; j++) { cin>>costmat[i][j]; costmat[i][i] = 0; DVR[i].dist[j] = costmat[i][j]; DVR[i].from[j] = j; } }

19 for(i = 0; i < nodes; i++) //We choose arbitary vertex k and we calculate the direct distance from the node i to k using the cost matrix and add the distance from k to node j for(j = i+; j < nodes; j++) for(k = 0; k < nodes; k++) if(dvr[i].dist[j] > costmat[i][k] + DVR[k].dist[j]) { //We calculate the minimum distance DVR[i].dist[j] = DVR[i].dist[k] + DVR[k].dist[j]; DVR[j].dist[i] = DVR[i].dist[j]; DVR[i].from[j] = k; DVR[j].from[i] = k; }

20 for(i = 0; i < nodes; i++) { cout<<"\n\n For router: "<<i+; for(j = 0; j < nodes; j++) cout<<"\t\n node "<<j+<<" via <<DVR[i].from[j]+ <<" Distance "<<DVR[i].dist[j]; } cout<<" \n\n "; return 0; }

21 6 Now run the program by considering this example and giving values like this and see the output Enter the number of nodes : Enter the cost matrix 0 (-) (-) (-) (-) (-) 0 (-) (-) 6 (-) (-) (-) 0 (-) (-) (-) 6 (-) (-) 0 (-)