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Computer Networks MCQ - SET 05
1. Which of the
following is an improvement of Internet Protocol version 6 (IPv6) over IPv4?
(a) Reduced IP
address space
(b) Better support
for QoS (Quality of Service)
(c) Less support
for mobility
(d) Complex network
configuration
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Ans : (b)
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Answer: (b)
Better support for QoS (Quality of Service)
IPv6 is the latest version of the
Internet Protocol, which identifies devices across the internet so they can
be located. The IPv6 protocol is 128-bits, consists of 8 numbered strings,
and each containing 4 characters, separated by a colon. This supports approximately
340 undecillions (trillion trillion trillions) addresses (devices). So, with
IPv6, we will not be running out of IP address spaces anytime soon.
It does not require Network Address
Translation (NAT) due to the very huge number of supported devices. No
address sharing is required. This ensures true end-to-end connectivity at the
IP layer. It enables new and valuable services. Peer-to-peer networks are
easier to create and maintain, and services such as VoIP and Quality of
Service (QoS) become more robust.
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2. Congestion
control works as _________ layer.
(a) Physical layer
(b) Data link layer
(c) Network layer
(d) Application
layer
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Ans : (c)
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Answer: (c)
Network layer
Congestion control is a network
layer issue, and is thus concerned with what happens when there is more data
in the network than can be sent with reasonable packet delays, no lost
packets, etc.
Difference between congestion
control and flow control
Flow control is local, congestion
control is global. One way of handling congestion is by using a flow control
mechanism to reduce the traffic put on the net by a particular host.
Congestion
control
Internet is used by many independent
users with restricted (less) resources to provide the link. If every user
sends data at very high rate, it will cause congestion and result in
unreliable transmission. Congestion control is essentially required for “reliable”
transmission at “fair-rate” with “high-resource utilization”. It is implemented in “Network Layer”.
Congestion control protocol is also
called as transport protocol. Transmission Control Protocol (TCP) and User
Datagram Protocol (UDP) are the congestion control protocols.
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3. What is the
typical size of the header for an IPv4 datagram?
(a) 10 bytes
(b) 20 bytes
(c) 30 bytes
(d) 16 bytes
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Ans : (b)
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Answer: (b)
20 bytes
The normal size of the IPv4 header
is 20 bytes, unless options are present (which is rare). An option exists
within the header that allows further optional bytes to be added, but this is
not normally used.
Because an IPv4 datagram can contain
a variable number of options (which are included in the IPv4 datagram header)
the 4 bits used by the header length are needed to determine where in the IP datagram
the data actually begins. Since the header length field is of 4 bits so the
maximum header length allowed is 60 bytes. Usually when no options are
present then the value of this field is 5. Here 5 means five 32 bit words i.e.
5 * 4 = 20 bytes.
Most IP datagram do not contain options
so the typical IP datagram has a 20 byte header.
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4. The Simple Mail
Transfer Protocol (SMTP) is an example of a
(a) transaction-oriented
application-layer protocol
(b) session-oriented
application-layer protocol
(c) transaction-oriented
transport-layer protocol
(d) session-oriented
transport-layer protocol
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Ans : (b)
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Answer: (b)
session-oriented application-layer protocol
Simple Mail Transfer Protocol is a
standard application-layer protocol for delivery of e-mail over a TCP/IP
internetwork such as the Internet. SMTP is responsible for feeding and
forwarding e-mails from sender to recipient.
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5. In the
Transmission Control Protocol (TCP), acknowledgements (ACKs) are used for:
(a) error control
(b) congestion
control
(c) error control
and flow control
(d)
error control, flow control, and congestion control
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Ans : (d)
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Answer: (d)
error control, flow control, and congestion control
TCP is a connection oriented
protocol over connection-less network IP. It is an acknowledgment (ACK) based
protocol. Hence, each end has to acknowledge the data received from other
end. This is achieved through ACK messages (or acknowledgement messages). For
TCP to work correctly every transferred byte needs to be acknowledged (only
then it will be a connection oriented protocol)(it is not true always. TCP windows are
used to handle).
If packets are not ACKed, the sender may retransmit the packets (or terminate
the connection if it thinks the receiver has crashed). This way, ACKs are
used for error control, flow control and congestion control in TCP
connections.
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