6 files changed, 194 insertions, 3 deletions

diff --git a/q2/ford.c b/q2/ford.c
new file mode 100644
index 0000000..993a0c3
--- /dev/null
+++ b/q2/ford.c
@@ -0,0 +1,78 @@
+#include <stdio.h>
+
+int A[10][10], n, d[10], p[10];
+
+int bellman_ford() {
+    int i, u, v;
+    for (int i = 0; i < n; i++) {
+        for (u = 0; u < n; u++) {
+            for (v = 0; v < n; v++) {
+                if (d[v] > d[u] + A[u][v]) {
+                    d[v] = d[u] + A[u][v];
+                    p[v] = u;
+                }
+            }
+        }
+    }
+    for (u = 0; u < n; u++) {
+        for (v = 0; v < n; v++) {
+            if (d[v] > d[u] + A[u][v]) {
+                printf("Detected negative edge\n");
+                return -1;
+            }
+        }
+    }
+    return 0;
+}
+
+int main() {
+    scanf("%d", &n);
+    int source = 0, destination = 0;
+    for (int i = 0; i < n; i++) {
+        for (int j = 0; j < n; j++) {
+            scanf("%d", &A[i][j]);
+        }
+    }
+    scanf("%d", &source);
+    scanf("%d", &destination);
+
+    printf("Input graph:\n");
+    for (int i = 0; i < n; i++) {
+        for (int j = 0; j < n; j++) {
+            printf("%3d ", A[i][j]);
+        }
+        printf("\n");
+    }
+
+    for (int i = 0; i < n; i++) {
+        d[i] = 999;
+        p[i] = -1;
+    }
+    d[source] = 0;
+    int valid = bellman_ford();
+    if (valid == -1) {
+        printf("Graph contains negative edge\n");
+        return 0;
+    }
+    printf("\nFrom Router %d to Router %d\n", source, destination);
+    // for(int i=0; i<n; i++){
+    //     printf("Cost: %2d | Path: ", d[i]);
+    //     if(i != source){
+    //         int j = i;
+    //         while(p[j] != -1){
+    //             printf("%d <- ",j);
+    //             j = p[j];
+    //         }
+    //     }
+    //     printf("%d\n",source);
+    // }
+    printf("Cost: %2d | Path: ", d[destination]);
+    if(destination != source){
+        int j = destination;
+        while(p[j] != -1){
+            printf("%d <- ",j);
+            j = p[j];
+        }
+    }
+    printf("%d\n",source);
+}
diff --git a/q3/checksum.c b/q3/checksum.c
new file mode 100644
index 0000000..513ae17
--- /dev/null
+++ b/q3/checksum.c
@@ -0,0 +1,37 @@
+#include <stdio.h>
+#include <stdio.h>
+
+int checksum() {
+    unsigned int parts[9];
+    unsigned int sum;
+    printf("Enter the parts, one per line:\n");
+    for (int i = 0; i < 9; i++) {
+        scanf("%X", &parts[i]);
+        sum += parts[i];
+        while (sum >> 16)
+            sum = (sum & 0xffff) + (sum >> 16);
+    }
+    return ~sum;
+}
+
+int main() {
+    printf("--- SENDER ---\n");
+    int sender_checksum = checksum();
+    printf("\n--- RECV ---\n");
+    int recv_checksum = checksum();
+    printf("Sent checksum: %x\n", sender_checksum);
+    printf("Recieved checksum: %x\n", recv_checksum);
+    if (sender_checksum == recv_checksum) {
+        printf("Matching checksums!\n");
+        return 0;
+    } else {
+        printf("Mismatched checksums!\n");
+        return 0;
+    }
+}
+
+// 00004500 00000073 00000000 00004000 00004011 0000c0a8 00000001 0000c0a8 000000c7
+// checksum - ffffb861
+
+// 00004500 0000003c 00001c46 00004000 00004006 0000ac10 00000a63 0000ac10 00000a0c
+// checksum - 0000b1e6
diff --git a/q3/checksum.o b/q3/checksum.o
new file mode 100755
index 0000000..cfcaed6
--- /dev/null
+++ b/q3/checksum.o
diff --git a/q3/hamming.c b/q3/hamming.c
new file mode 100644
index 0000000..01d0f0e
--- /dev/null
+++ b/q3/hamming.c
@@ -0,0 +1,56 @@
+#include<stdio.h>
+
+void main() {
+    int data[10];
+    int dataatrec[10],c,c1,c2,c3,i;
+
+    printf("Sender: ");
+    scanf("%d %d %d %d",&data[0] ,&data[1] ,&data[2] ,&data[4]);
+
+    //Calculation of even parity
+    data[6]=data[0]^data[2]^data[4];
+    data[5]=data[0]^data[1]^data[4];
+    data[3]=data[0]^data[1]^data[2];
+
+    printf("Encoded Data: ");
+    for(i=0;i<7;i++)
+        printf("%d",data[i]);
+
+    printf("\nReceiver: ");
+    for(i=0;i<7;i++)
+        scanf("%d",&dataatrec[i]);
+
+    c1=dataatrec[6]^dataatrec[4]^dataatrec[2]^dataatrec[0];
+    c2=dataatrec[5]^dataatrec[4]^dataatrec[1]^dataatrec[0];
+    c3=dataatrec[3]^dataatrec[2]^dataatrec[1]^dataatrec[0];
+    c=c3*4+c2*2+c1 ;
+
+    printf("\nSyndrome bits:  %d %d %d", c1, c2, c3);
+
+    if(c==0) {
+        printf("\nNo error while transmission of data\n");
+    }
+    else {
+        printf("\nError Position: %d",c);
+
+        printf("\nData sent: ");
+        for(i=0;i<7;i++)
+            printf("%d",data[i]);
+
+        printf("\nData received: ");
+        for(i=0;i<7;i++)
+            printf("%d",dataatrec[i]);
+
+        printf("\nCorrect message is: ");
+
+        //if errorneous bit is 0 we complement it else vice versa
+        if(dataatrec[7-c]==0)
+            dataatrec[7-c]=1;
+        else
+            dataatrec[7-c]=0;
+
+        for (i=0;i<7;i++) {
+            printf("%d",dataatrec[i]);
+        }
+    }
+}
diff --git a/q3/hamming.o b/q3/hamming.o
new file mode 100755
index 0000000..fa9cb70
--- /dev/null
+++ b/q3/hamming.o
diff --git a/readme.txt b/readme.txt
index 6aabaaf..5caeacf 100644
--- a/readme.txt
+++ b/readme.txt
@@ -1,5 +1,7 @@
 18CS54 - network programming and security
-------------------------------------------------------------
+============================================================
+
+
 Q1: Write a networking program consisting of a client and
     server components. The client must request for a file by
     providing a file name, and the server must respond with the
@@ -9,8 +11,26 @@ Q1: Write a networking program consisting of a client and
 
 A1: https://u.peppe.rs/qt.png
 
+------------------------------------------------------------
+
+Q2: Write a program to illustrate the function of
+    Distance-Vector routing using Bellman-Ford algorithm. Handle
+    the situation where negative edges are present.
+
+A2: https://u.peppe.rs/LS.png
+    https://u.peppe.rs/ep.png
+
+------------------------------------------------------------
+
+Q3: Write a program to showcase
+    a) Checksum - error detection
+    b) Hamming code - error detection and correction
+
+A3: https://u.peppe.rs/qQ.png
+    https://u.peppe.rs/qr.png
 
 ------------------------------------------------------------
+
 Q6: Write a networking program to demonstrate the following:
     a) Concurrent TCP server
     b) Iterative TCP server
@@ -20,8 +40,8 @@ A6: a) https://u.peppe.rs/E3.png
     b) https://u.peppe.rs/VA.png
     c) https://u.peppe.rs/ei.png
 
-
 ------------------------------------------------------------
+
 Q7: Write a networking program that recieves a shell command
     from a client and returns the output of the command to the
     client.
@@ -29,5 +49,5 @@ Q7: Write a networking program that recieves a shell command
 A7: https://u.peppe.rs/QD.png
 
 
-------------------------------------------------------------
+============================================================
 mirror of git.peppe.rs/university/nps