Tests with answers




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Computer Networks


Tests with answers

  1. The Internet Control Message Protocol (ICMP) allows

Answer: The exchange of error messages among routers and hosts

  1. Layered protocol architectures

Answer: are widely used because they ensure scalability and simplicity

  1. The SMTP Protocol

Answer: is used for the delivery of outgoing electronic mail messages from a client to server

  1. In a stop & wait AR protocol

Answer: a device can send only one packet and then it has to stop, waiting for an acknowledge

  1. In a Sliding Window transmission protocol (e.g., Go-Back-N)

Answer: a device can send out an arbitrary number of packets without waiting for acknowledge

  1. A possible IP network that can be assigned to an Ethernet network containing 200 nodes is

Answer: 130.192.2.0/24

  1. Two IP nodes 130.192.40.1/24 e 130.192.40.200/24

Answer: can directly exchange IP packets

  1. In the CSMA/CD protocol, a station completes the transmission of a frame

Answer: only if, sensing the channel, it doesn’t detect an eventual simultaneous reception with the current transmission

  1. Congestion control in TCP

Answer: limits the size of the transmission window

  1. The Internet network

Answer: is based on packet switching

  1. In a packet switched network, the routing is

Answer: the process use for determining the source-destination routes taken by packets, i.e., for writing the routing table

  1. The IP protocol provides a service that is

Answer: unreliable (i.e., without any delivery guarantee) and connectionless

  1. End-to-end error recovery over the Internet, when available

Answer: is implemented at the Transport Layer.

  1. The IP header, i.e., the IP PCI, mandatorily contains

Answer: The Time To Live (TTL) field that enables removing from the network packets that were forwarded by too many routers / the code field, …tcp

  1. During the slow-start phase of the TCP congestion control, the transmission window size of the sender

Answer: grows of one segment at every received acknowledgement

  1. The flow control in the TCP protocol

Answer: is based on some information included into the segments sent from the receiver to the sender

  1. The end-to-end delay in a computer network

Answer: depends on the network load

  1. An Ethernet Switch, when it receives an ARP request packet

Answer: forwards it on all ports, except the one over which the packet has been received

  1. A DHCP server deployed in a local area network provides

Answer: an IP configuration to hosts connected to the local area network

  1. The which access network separates data and phone calls on the same transmission media between the user equipments and the ISP equipments

Answer: frequency division multiplexing

  1. A network protocol is

Answer: a set of rules that devices must user for communications

  1. Which among the followings is a distinctive function of the Link in a networking layered architecture?

Answer: delivery of packets (referred to as frames at this layer) among neighboring nodes

  1. The congestion control for the Transmission Control Protocol (TCP) is based

Answer: on the adjustment of the transmission window size according to the memory availability at the receiver

  1. The POP3 Protocol

Answer: can be used to transfer electronic mail messages from a server to client installed on a PC

  1. The PING program is

Answer: based on Echo Request and Echo Reeply ICMP messages

  1. The class C IPv4 addresses distinguish:

Answer: (a few) networks with a large number of hosts

  1. TCP dynamically changes the transmission window size to obtain

Answer: only flow control

  1. The introduction of subnet masks in the Internet addressing

Answer: enables the utilization of a single logical IP network over more than one physical network

  1. TCP segments

Answer: have a variable size that is selected on the basis of the congestion level in the network

  1. The Address Resolution Protocol (ARP)

Answer: disallows a host to obtain an IP address
Answer: achieves a translation function between layer-3 addresses and layer-2 addresses

  1. The header of a data packet in a packed switching network with datagram service includes

Answer: the addresses of the source and destination nodes

  1. The throughput (i.e., the amount of transferred bits per second) offered to a traffic flow

Answer: is given by the lowest throughput offered in all the traversed links, i.e., the bottleneck

  1. The packet switching technology

Answer: Ensures efficient bandwidth utilization

  1. An Ethernet swich is

Answer: a network node that forwards frame on the basis of MAC address

  1. In a routing table, the next-hop column of a static route is

Answer: the IP address of a remote interface directly connected to the router

  1. The Network Layer of the Internet protocol stack

Answer: Is based on the IP protocol

  1. Transport layer of the internet protocol stack

Answer: Might open connections before sending data

  1. The core of the Internet network

Answer: is a network based on mesh of interconnected switches

  1. The Ethernet technology

Answer: is based on CSMA/CD protocol

  1. The HTTP protocol

Answer: uses one or more TCP connections

  1. A client operating according to the selective-respect protocol (based on packets)

Answer: retransmits only the packet that caused the timer expiration



  1. The Network Layer

Answer: is over the Link Layer and below the Transport Layer

  1. The Ethernet technology

Answer: can be based on switches in order to obtain better performance
44. After having identified the correct output port, an IP router
Answer: modifies the Time To Live and Header Checksum field of the datagram header

  1. If a router receives an IP packet with correct checksum ,TTL=9 , and equal IP sourse and IP destination addresses

Answer: it forwards the packet to the destination

  1. Let’s consider a host who is transmitting data by means of TCP .Give a current value for the transmission window size equal to 10 segments , with a maximum receive window equal to 40 segments, when the sender receives a segment containing an acknowledgment from the receiver , which to the following situations is impossible?

Answer: the current value of the transmission window size becomes equal to 51 segments

  1. The IP version 4 addresses are:

Answer: of fixed total length, but consisting of a variable length part identifying the network and a variable length part identifying the host

  1. The destination IP address in an IP packet is

Answer: a fundamental header field, used by routers to forward the packet

  1. The header of a data packet in a packed switching network with datagram service includes

Answer: the addresses of the source and destination nodes

  1. During the slow-start phase of the TCP congestion control, the transmission window size of the sender

Answer: doubles at every received acknowledgement

  1. The DSL access network separates data and phone calls on the same transmission media between the user equipments and the ISP equipments using

Answer: frequency division multiplexing

  1. Which of the following claims is false?

Answer: A host transmits IP packets only to hosts whose net_id is equal to its own net_id.
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