source host segments long, application$-$layer messages $($for example, an image or a music file$)$ into smaller packets and sends the packets into the network. The receiver then reassembles the packets back into the original message. We refer to this process as message segmentation. Figure $1\mathrm{.}27$ illustrates the end$-$to$-$end transport of a message with and without message segmentation. Consider a message that is ${10}^6$ bits long that is to be sent from source to destination in Figure $1\mathrm{.}27.$ Suppose each link in the figure is $5Mbps.$ Ignore propagation, queuing, and processing delays.

a$.$ Consider sending the message from source to destination without message segmentation. How long does it take to move the message from the source host to the first packet switch? Keeping in mind that each switch uses store$-$and$-$forward packet switching, what is the total time to move the message from source host to destination host?