Consider a source computer (S) transmitting a file of size $2 * 10^6$ bits to a destination computer (D) over a network of three routers ($R_1$, $R_2$ and $R_3$) and four links $(L_1, L_2, L_3 and L_4)$. $L_1$ connects $S$ to $R_1$; $L_2$ connects $R_1$ to $R_2$; $L_3$ connects $R_2$ to $R_3$; and $L_3$ connects $R_3$; and $L_3$ connects $R_3$ to $D$. Let each link be of length $100$ km. Assume signals travel over each link at a speed of $10^8$ meters per second. Assume that the link bandwidth on each link is $1$ Mbps. Let the file be broken down into $2000$ packets each of size $100$ bits. What is the total sum of transmission and propagation delays in transmitting the file from $S$ to $D$?
a. 1007 ms
b. 1010 ms
c. 2010 ms
d 2007 ms
