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Monday, 2 November 2020

Computer networks multiple choice questions with answers 05

Computer networks multiple choice questions with answers, entrance exam quiz questions on computer networks, solved exam questions on computer networks, MCQ in CN

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

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.


2. Congestion control works as _________ layer.

(a) Physical layer

(b) Data link layer

(c) Network layer

(d) Application layer

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.


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

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.


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

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.


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

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.




Related links



What for ACKs are used in TCP connection

SMTP is a session-oriented application layer protocol

Why the typical size of IP datagram header is  20 bytes?

What are the differences between congestion control and flow control

Computer networks solved question and answers


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