Wednesday, September 16, 2020

Computer Networks multiple choice questions set 03

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 03



1. Negative ACKnowledgements (NAKs) are not needed in a Reliable Data Transfer (RDT) protocol if:

(a) sequence numbers are being used

(b) timeouts and retransmissions are being used

(c) checksums are being used

(d) wireless is being used

Answer: (b) timeouts and retransmissions are being used

Negative ACKnowledgement (NAK) is an abbreviation for negative acknowledgment or not acknowledged. It is a feedback message that tells the sender that a message was not successfully received.

Reliable data transfer (RDT) protocol is used to ensure delivery of all packets and to enable the receiver to deliver the packets.

NAKs are not needed in a RDT protocol if timeouts and retransmissions are used.


2. In a datagram network, packet reordering is handled:

(a) at the ingress router

(b) at the egress router

(c) with clever buffer management in routers

(d) at the end systems

Answer: (d) at the end systems

In a datagram network, each packet is treated independently of all others. Even if a packet is part of a multi packet transmission, the network treats it as though it existed alone. Packets in this approach are referred to as datagrams.

The datagrams, that belong to the same message, may travel through different paths before reaching their destination. This can cause the datagrams of a transmission to arrive at their destination out of order with different delays between the packets. Hence, the packet re-ordering is handled at the end systems.


3. The Internet Protocol (IPv4) is an example of a:

(a) connection-less network layer protocol

(b) connection-oriented network layer protocol

(c) connection-less transport layer protocol

(d) connection-oriented transport layer protocol

Answer: (a) connection-less network layer protocol

IPv4 is a connection-less protocol used in packet-switched networks. This protocol works at the network layer of the OSI model and at the Internet layer of the TCP/IP model. Thus this protocol has the responsibility of identifying hosts based upon their logical addresses and to route data among them over the underlying network.


4. The typical Maximum Segment Size (MSS) for TCP on the Internet is

(a) 64 bytes

(b) 128 bytes

(c) 1460 bytes

(d) 1024 bytes

Answer: (c) 1460 bytes

The maximum segment size (MSS) is a parameter of the options field of the TCP header that specifies the largest amount of data, specified in bytes, that a computer or communications device can receive in a single TCP segment. (Wikipedia)

The default size is 1460 bytes. The MSS will dictate the maximum size of the data part of the packet.

Essentially, the MSS is equal to MTU minus the size of a TCP header and an IP header:

MTU - (TCP header + IP header) = MSS

Refer more for 'What is MSS' here.


5. Routers and switches are working in the layers

(a) Network layer, Data link layer

(b) Data link layer, Transport layer

(c) Network layer, Transport layer

(d) Data link layer, Network layer

Answer: (a) Network layer, Data link layer

Routers operate at network layer and switches operate at data link layer.

Routers operate on the third layer of the OSI Model, the Network-Control Layer.  Rather than passing packets based on the Media Access Control (MAC) Layer addresses (as bridges do), a router examines the packet's data structure and determines whether or not to forward it. This determination is made based on the network information within the packet. (Click here for more)

An Ethernet switch operates at the data link layer (layer 2) of the OSI model to create a separate collision domain for each switch port. The primary function of a switch is to determine the MAC addresses of all the devices which are connected to make sure that where the data is supposed to be sent.



Related links



In which layers, router and switches are working

What is maximum segment size (MSS) for TCP

IPv4 is an example of connection-less network layer protocol

Who is handling the packet reordering in datagram network

What is the use of Reliable Data Trasfer (RDT) protocol

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