P$31.$ In modern packet$-$switched networks, including the Internet, the 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 $8*106$ bits long that is to be sent from source to destination in Figure $1\mathrm{.}27.$

Suppose each link in the figure is $2Mbps.$ 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?

b$.$ Now suppose that the message is segmented into $800$ packets, with each packet being

$10,000$ bits long. How long does it take to move the first packet from source host to the

first switch? When the first packet is being sent from the first switch to the second switch,

the second packet is being sent from the source host to the first switch. At what time will

the second packet be fully received at the first switch?

c$.$ How long does it take to move the file from source host to destination host when

message segmentation is used? Compare this result with your answer in part $($a$)$ and

comment.d$.$ In addition to reducing delay, what are reasons to use message segmentation?

e$.$ Discuss the drawbacks of message segmentation.