What's the difference between packet transmission delay and propagation delay?

Difference between packet transmission delay and propagation delay:

Suppose there are two hosts H1 and H2. H1 and H2 are connected by a network or communication links (transmission media). H1 wants to send some packets (bits) to H2.

Now the time taken to place the complete data packets on the transmission media/link is called a transmission delay (Td).

If we want to put a large packet on the link, it will take more time. In addition to that if the link has more capacity/bandwidth, the time required will be less as compared to the link with less bandwidth.

So, obviously, this Td will depend on the length of the packet and bandwidth of the link.

Td= length of the data packet(l) / bandwidth of the network (BW)

So for example, if l=1000 bit and BW= 1K bits/sec,

then Td=1sec

So, we can understand that transmission delay just involves the time to place the packet in the network. But yet the data packet till not reached to H2.

Propagation delay (Tp): Time taken to transfer 1 bit from H1 to H2 is called Propagation delay.

Now, we can think if the distance between H1 and H2 is large, definitely the Tp will be more. Moreover, Tp will also depend on the speed of the signal (like the speed of a car).

Tp= distance (d)/ transmission speed (s)

So for example, if d=9km and s= 3 xX10 ^8 m/sec,

then Td =3 X 10 ^-5 sec