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(COMP361)[2010](s)midterm~420^_10215.pdf
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PROBLEM 1 Suggested solution: 1) False.
Networks of many kinds (not just Ethernets) are connected together to form the Internet.
2) True.
3) False.

SMTP is used to transfer mail from the senders mail server to the recipients mail server; SMTP is also used to transfer mail from the senders user agent to the senders mail server. IMAP and POP3 are used to transfer mail from the recipients mail server to the recipients user agent.
4) True.
5) False.
You can still contact the machines using their IP addresses.

6) False. Even though VoIP typically does use UDP, this is not because UDP can provide the needed end-to-end delay guarantee, rather because without the .ow and congestion mechanisms like in TCP, UDP has better chance of providing smaller delay.
7) True.
8) False. Notice that a protocol over a connection-oriented protocol does not have to be a connection-oriented protocol, just like a protocol over a connectionless protocol (IP) does not have to connectionless (TCP is indeed connection-oriented protocol, while UDP is connectionless). The central characteristic of a connection-oriented protocol is that it needs at the minimum to maintain connection status information at both sides.
9) False. Propagation delay depends on the propagation speed and the distance. 10) False. VC cannot guarantee reliable data transmission only by itself and reliability is achieved by TCP service.
PROBLEM 2 Suggested solution: 1) Five layers. (1 point for each terminology)
.
Application layer: Message.

.
Transport layer: TCP Segment or UDP Datagram.

.
Network layer: Packet or Datagram.

.
Data-Link layer: Frame.


. Physical layer: Bit. 2) This is achieved through a combination of connection service and dedicated resource (link bandwidth and etc.) 3) Flow control and congestion control are two distinct control mechanisms with distinct objectives. Flow control makes sure that the sender does not overwhelm the receive buffers by sending too many packets too fast. Congestion control regulates the amount of data that an application can send into the network, helping to prevent congestion in the network core (i.e., in the buffers in the network routers). 4) Recursive query is one where the DNS server will fully answer the query (or give an error). In a recursive query a DNS server will, on behalf of the client (resolver), chase the trail of DNS to the other DNS servers to get the real answer to the question. An Iterative (or non-recursive) query is one where the DNS server may provide a partial answer to the query
(or give an error) known as referral and the resolver will have to contact new name server directly for further queries.
PROBLEM 3 Suggested solution:
1) dtotal = dproc + dqueu + dtran + dprop 2)
Da = 2L/R + d/c = 2 . 30M/10M + 104 . 103/(2 . 108) = 6.05sec
3)
Db = L/R + 1/3 . L/R + d/c = 4/3 . 30M/10M + 104 . 103/(2 . 108) = 4.05sec
PROBLEM 4 Suggested solution: The delay is S + hF 1 Fh
()(+ l . 1)=