Computer networks multiple choice questions with answers 08

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Computer Networks MCQ - SET 08

1. What are the types of acknowledgements (ACKs) used in typical TCP implementation?

(a) Selective ACKs only

(b) Both selective and cumulative ACKs

(c) Both positive and negative ACKs

(d) Positive, cumulative, selective and lookahead ACKs

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Ans : (d)

Answer: (d) Positive, cumulative, selective and lookahead ACKs TCP is a connection-oriented protocol. It guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent. It uses acknowledgements to ensure the integrity of the data flow. Positive ACK: acknowledgement to the sender on correctly received packets. Cumulative ACK: acknowledgement on reception of data packets with the sequence number of highest in-order data received. Selective ACK: acknowledgement that indicates the sequence number of every data packet received. Lookahead ACK: the use of sequence number used as acknowledgement number.

 

2. What would be the approximate transmission time a 10 Mbps (Megabits per second) Ethernet LAN take to send a 1200 byte data packet?

(a) 1 ms

(b) 2 ms

(c) 5 ms

(d) 10 ms

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Ans : (a)

Answer: (a) 1 ms Packet transmission time can be calculated as follows; Transmission time = Packet size (in bits) / Transmission rate (in bits/s) For this question; Transmission time = (1200 * 8 bit) / (10 * 106 bits/sec) = 0.00096 sec ≈ 1 ms.

 

3. Internet Message Access Protocol (IMAP) runs between email

(a) sender’s mail client and sender’s outgoing mail server

(b) receiver’s mail client and receiver’s incoming mail server

(c) sender’s mail server and receiver’s mail server

(d) sender’s mail client and receiver’s mail client

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Ans : (b)

Answer: (b) receiver’s mail client and receiver’s incoming mail server IMAP was designed with the goal of permitting complete management of an email box by multiple email clients, therefore clients generally leave messages on the server until the user explicitly deletes them. Whenever you check your inbox, your email client contacts the server to connect you with your messages. When you read an email message using IMAP, you aren’t actually downloading or storing it on your computer; instead, you are reading it off of the server. As a result, it’s possible to check your email from several different devices without missing a thing. [Refer here for more]

 

4. Let us suppose that all of the network sources occasionally have data to send over the network. Which of the following would be most suitable for such a scenario?

(a) Circuit switching

(b) Packet switching

(c) Both circuit and packet switching

(d) Neither of them is true

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Ans : (b)

Answer: (b) Packet switching Packet-switching is better here because there are statistical multiplexing gains – when a source does not have data to send, it will not be allocated bandwidth (that would be idle). Hence this bandwidth is available for use by other sources.

 

5. Which among the following protocols has out-of-band control messages?

(a) HTTP

(b) TCP

(c) SMTP

(d) FTP

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Ans : (d)

Answer: (d) File Transfer Protocol (FTP) Out-of-band control is a characteristic of network protocols with which data control is regulated. Out-of-band control passes control data on a separate connection from main data. Protocols such as FTP use out-of-band control. FTP handles control information in one connection and the data files in the other. HTTP, TCP and SMTP have in-band control messages. It means that control message and data messages may be interleaved with each other on the same connection.

 

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Related links

 

• Computer Networks MCQ home page

 

Why do we use ACK in TCP?

Why packet switching is better than circuit switching for the network resources that send occasionally?

Define Internet Message Access Protocol (IMAP)

How to calculate the transmission time required to send a data packet over network?

Multiple choice questions in computer networks

Computer networks multiple choice questions with answers 07

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Computer Networks MCQ - SET 07

1. Key difference between User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) is

(a) TCP is connection-oriented, while UDP is connection-less

(b) UDP is a reliable byte stream protocol, while TCP is not

(c) UDP uses sequence numbers, while TCP does not

(d) UDP enforces flow control, while TCP has no flow control

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Ans : (a)

Answer: (a) TCP is connection-oriented, while UDP is connection-less The Transmission Control Protocol (TCP) helps to: ensure the recipient receives all of the data that’s sent (via a delivery receipt), and keep the data transmissions organized by ensuring that packets are received by the recipient in their intended order. Hence, TCP is a connection-oriented communication protocol. On the other hand, User Datagram Protocol (UDP) requires no connection to be established prior to sending your data packets (or, more specifically, datagrams). [Please refer here for more on TCP and UDP]

 

2. How IPv6 is different from IPv4?

(a) Quality of Service is better in IPv4

(b) Expanded IP address space for IPv6

(c) IPv4 is better than IPv6 in terms of support for mobility

(d) None of the above

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Ans : (b)

Answer: (b) Expanded IP address space for IPv6 Internet Protocol version 6 (IPv6): IPv4 is based on 32-bit addressing, limiting it to a total of 4.3 billion addresses. IPv6 is based on 128-bit addressing and can support 340 undecillion, which is 340 trillion addresses. Having more addresses has grown in importance with the expansion of smart devices and connectivity. IPv6 provides more than enough globally unique IP addresses for every networked device currently on the planet, helping ensure providers can keep pace with the expected proliferation of IP-based devices. [Please refer here for more on IPv6]

 

3. Transmission Control Protocol (TCP) supports _____ data transfers?

(a) Full-duplex

(b) Half-duplex

(c) Simplex

(d) None of the above

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Ans : (a)

Answer: (a) Full-duplex TCP is a transport-layer protocol that provides a reliable, full duplex, connection-oriented data transmission service. It is full-duplex because it can send and receive the data from both the side of connection simultaneously, without requiring line turnarounds, at the API level. "If there is a TCP connection between Process A on one host and Process B on another host, then application layer data can flow from Process A to Process B at the same time as application layer data flows from Process B to Process A". Another explanation: Full duplex or not is depend on the type of the Ethernet connection. If the switches and cabling support full duplex the TCP connection will work on full duplex but if those only support half duplex the TCP connection will work as half duplex. The speed and duplex setting are not features of TCP those are inherited and are part of a lower OSI layer, the transport layer. [Please refer here for details]

 

4. The field “Window” or “Window size” in TCP header refers to

(a) sender window

(b) receiver window

(c) congestion window

(d) none of the above

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Ans : (b)

Answer: (b) receiver window The Window size is considered to be one of the most important flags within the TCP header. The size specifies the amount of data the destination is willing to accept from the sender. The sending host can send only that size of data before it must wait for an acknowledgment and window update from the receiving host. The window size flag consumes 16 bits. TCP supports flow control and the window size field is used for flow control.

 

5. The strength of signal falls off with distance over any transmission medium is called

(a) Attenuation

(b) Data rate

(c) Channel capacity

(d) Signal strength ratio

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Ans : (a)

Answer: (a) Attenuation Attenuation is the loss of signal strength that occurs in networking cables or connections during transmission of signal from place to place. This happens when a signal loses energy overcoming the resistance of the medium in which it is traveling. Attenuation typically is measured in decibels (dB) or voltage and can occur due to a variety of factors.

 

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Related links

 

• Computer Networks MCQ home page

 

Define the term attenuation in networking

TCP supports full-duplex communication

State the key difference between TCP and UDP

How IPv6 is different from IPv4

Multiple choice questions in computer networks

Computer networks multiple choice questions with answers 06

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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 06

1. The Domain Name Service (DNS) 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 : (a)

Answer: (a) transaction-oriented application-layer protocol Domain name service (DNS) is the application service that translates the IP address into a more recognized and memorable name. Whenever using the Internet, there are millions of DNS servers that translate any uniform resource locator (URL) typed into the location field of any Web browser into a specific IP address. The Domain Name System (or DNS) converts human readable domain names (like: www.google.com) into Internet Protocol (IP) addresses (like: 173.194.39.78).

 

2. Which of the following is an advantage of persistent HTTP connection?

(a) additional RTT's when obtaining multiple Web objects from different Web servers

(b) re-using an existing TCP connection for a Web transfer when it is possible to do so

(c) increased latency on subsequent requests

(d) None of the above

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Ans : (b)

Answer: (b) re-using an existing TCP connection for a Web transfer when it is possible to do so A persistent connection takes 2 RTT for the connection and then transfers as many objects, as wanted, over this single connection. By opening and closing fewer TCP connections, CPU time is saved in routers and hosts (clients, servers, proxies, gateways, tunnels, or caches), and memory used for TCP protocol control blocks can be saved in hosts.

 

3. Which of the following is used by the network application BitTorrent?

(a) the peer-to-peer file sharing and TCP

(b) the peer-to-peer file sharing and UDP

(c) the client-server file sharing and TCP

(d) the client-server file sharing and UDP

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Ans : (a)

Answer: (a) the peer-to-peer file sharing and TCP BitTorrent is a communication protocol for peer-to-peer file sharing (P2P), which enables users to distribute data and electronic files over the Internet in a decentralized manner. Rather than downloading a file from a single source server, the BitTorrent protocol allows users to join a "swarm" of hosts to upload and download from each other simultaneously. Refer Wikipedia.

 

4. In general, the throughput achieved by TCP for a
file transfer is

(a) inversely proportional to the average window size used during the transfer

(b) inversely proportional to the round trip time of the network path

(c) inversely proportional to the TCP segment size used for the transfer

(d) all of the above

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Ans : (b)

Answer: (b) inversely proportional to the round trip time of the network path An important measure of the performance of a TCP connection is its throughput - the rate at which it transmits data from the sender to the receiver.  Clearly, throughput will depend on the value of w (window size). If a TCP sender transmits all w segments back-to-back, it must then wait for one round trip time (RTT) until it receives acknowledgments for these segments, at which point it can send w additional segments. If a connection transmits w segments of size MSS (maximum segment size) bytes every RTT seconds, then the connection's throughput, or transmission rate, is  (w*MSS)/RTT bytes per second.

 

5. For a TCP segment header, the minimum size is

(a) 20 bytes

(b) 25 bytes

(c) 10 – 12 bytes

(d) 16 bits

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Ans : (a)

Answer: (a) 20 bytes The minimum size header is 5 words and the maximum is 15 words thus giving the minimum size of 20 bytes and maximum of 60 bytes, allowing for up to 40 bytes of options in the header.  TCP wraps each data packet with a header containing 10 mandatory fields totaling 20 bytes (or octets). Each header holds information about the connection and the current data being sent.

 

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Related links

 

• Computer Networks MCQ home page

 

What is an advantage of persistent HTTP connection?

What does DNS do?

Domain Name Service is a transaction oriented application layer protocol

How many RTTs a persistent http connection takes

What type of file sharing is done by BitTorrent

How do you relate TCP throughput and Round Trip Time

Computer networks multiple choice questions with answers 05

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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

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Ans : (b)

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

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Ans : (c)

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

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Ans : (b)

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

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Ans : (b)

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

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Ans : (d)

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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Related links

 

• Computer Networks MCQ home page

 

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