d)
i. Without message segmentation, if bit errors are not tolerated, if there is a
single bit error, the whole message has to be retransmitted (rather than a single
packet).
ii. Without message segmentation, huge packets (containing HD videos, for
example) are sent into the network. Routers have to accommodate these huge
packets. Smaller packets have to queue behind enormous packets and suffer
unfair delays.
e)
i. Packets have to be put in sequence at the destination.
ii. Message segmentation results in many smaller packets. Since header size is
usually the same for all packets regardless of their size, with message
segmentation the total amount of header bytes is more.
Problem 32
Yes, the delays in the applet correspond to the delays in the Problem 31.The propagation
delays affect the overall end-to-end delays both for packet switching and message
switching equally.
Problem 33
There are F/S packets. Each packet is S=80 bits. Time at which the last packet is received
at the first router is
S
F
R
S 80
sec. At this time, the first F/S-2 packets are at the
destination, and the F/S-1 packet is at the second router. The last packet must then be
transmitted by the first router and the second router, with each transmission taking
R
S 80
sec. Thus delay in sending the whole file is
)2(
80
S
F
R
S
delay
To calculate the value of S which leads to the minimum delay,
FSdelay
dS
d
400
Problem 34
The circuit-switched telephone networks and the Internet are connected together at
"gateways". When a Skype user (connected to the Internet) calls an ordinary telephone, a
circuit is established between a gateway and the telephone user over the circuit switched
network. The skype user's voice is sent in packets over the Internet to the gateway. At the
gateway, the voice signal is reconstructed and then sent over the circuit. In the other
direction, the voice signal is sent over the circuit switched network to the gateway. The
gateway packetizes the voice signal and sends the voice packets to the Skype user.
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