Computer Networks Quiz PDF

COMPUTER NETWORKS QUIZ Telegram bot version: https://t.me/networks_quiz_bot Additional quizzes (unofficial and unverified): Drive 02 Drop At the bottom of the file you will find the questions from the Networks orals. Along with the questions for the final Not exam Edit the file for...

COMPUTER NETWORKS QUIZ Telegram bot version: https://t.me/networks_quiz_bot Additional quizzes (unofficial and unverified): Drive 02 Drop At the bottom of the file you will find the questions from the Networks orals. Along with the questions for the final Not exam Edit the file for personal purposes, you will break the bot! Only edit it To contribute to quizzes while respecting correct formatting, thank you! Before editing any verified answers compare yourself on the network group connected to the telegram bot t.me/inginf_bot So that others can also evaluate whether the previous answer is wrong or not! SLIDE CHAPTERS. 3) Fundamentals of data transmission 4) Audio and video 5) TLC Networks 5) TLC Networks 2 6) Network architectures and protocols Exercise 1. Common channel signaling requires that. A) Control apparatuses o f switching stations exchange packet-switched signaling information B) Each channel dedicated to user data transmission is associated with a different channel for signaling C) Signaling between switching stations is done by sharing a single channel via satellite Answer: A verified. Comment: In common channel signaling, user information travels on separate channels but with a single signaling channel used to control the signaling of all user channels. The signaling channel operates as a packet. Exercise 2. The characteristics of a fully connected mesh topology are. A) High channel count, good fault tolerance, easy routing B) High channel count, good fault tolerance, difficult routing C) Low channel count, poor fault tolerance, difficult routing Answer: A verified. Comment: see transparencies "Mesh Topology." In the fully connected mesh there is always a direct way between each node. Exercise 3. Conversational interactive telecommunications services are characterized by. A) Low probability of error in information transfer B) Real-time information transfer C) Storage of information on the network and delivery to the recipient in deferred time Answer: B verified. Comment: In conversational interactive services, communication takes place with the transfer of information from end to end in real time. See "Conversational interactive services" transparencies. Exercise 4. In packet-switched networks, the factors that cause small packets to be chosen are. A) Lower incidence of control information, higher efficiency in transferring large SDUs B) Better possibility of parallelization, lower transfer delay, lower probability of error on the bit C) Better possibility of parallelization, lower packetization delay, lower probability of error on packet Answer: C verified. Comment: Packet length is determined by: parallelization possibility (pipeline), packetization delay, percentage of control information. Short packets favor parallel transmission over different channels of packets of the same communication, short packets reduce packetization delay (important for voice traffic over a packet network), long packets reduce the percentage of control information. Exercise 5. In the OSI model, the transport layer provides services A) Relying on services from the application layer B) Based on the services provided by the network layer C) Based on the services provided by the session level Answer: B verified. Comment: Think of the ISO/OSI stack. See transparencies on the OSI model. Exercise 6. Which of the following statements is in accordance with the ISO/OSI reference model? A) One (N)-entity and one (N-1)-entity can have the same address. B) One (N)-entity can be associated with two different (N-1)-addresses. C) Two (N)-entities can be associated with the same (N-1)-address. Answer: B verified. Comment: Each entity is characterized by the abbreviation (address) of its layer, so A and C are wrong and by exclusion the correct answer is B. Internet source. Exercise 7. In a Go-Back-N type window protocol, it may be convenient to increase the size of the transmission window (measure in number of data)  A) When transmission speed increases at equal data unit size and equal data unit transfer delays between transmitter and receiver B) When decreasing the transmission rate at equal data unit size.and equal unit transfer delays between transmitter and receiver C) When the distance between transmitter and receiver decreases, thus the transfer delays of data units, without changing the transmission speed D) When the probability of error on the channel increases Answer: A verified. Comment: Efficiency of a window protocol. Assuming n=k, we have Wt=k(1+2*(tp/tx)). As the transmission rate increases, the transmission time tx decreases, imposing an increase in Wt to keep the efficiency equal to k. Exercise 8. A Go-Back-N type window protocol does not require an increase in complexity compared to a Stop- And-Wait with respect to A) Amount of memory required at the transmitter B) Minimum amount of sequence numbers required to distinguish data units C) Amount of memory required at the receiver Answer: C verified. Comment: Go-Back-N does not require an increase in complexity over the receive window at the receiver. For Stop and Wait 𝑊 = 1 and for Go-Back-N 𝑊 = 1. 𝑅 𝑅 Exercise 9. Aloha and S-Aloha protocols. A) To avoid interference between the transmissions of users sharing a broadcast channel assign each user a fixed time interval in which to broadcast B) They do not implement any preventive control to avoid interference between transmissions of users sharing a broadcast channel; only in the case of interference (collision) is action taken, repeating the transmission after a fixed delay C) They do not implement any preventive control to prevent interference between t h e transmissions of users sharing a broadcast channel; Only in the case of interference (collision) is action taken, repeating the transmission after a random delay Answer: C verified. Comment: Aloha has low efficiency because nodes transmit without coordinating with each other, only in the case of a collision is a backoff performed: the two (or more) stations that collided wait for a random time before retransmitting the PDU. The random time is used to break determinism and if in the case the two (or more) stations wait the same time, a collision with probability 1 would occur again. In this case, the maximum random waiting time is doubled. Exercise 10. The architecture of Internet protocols is organized A) In seven levels B) In four levels  C) In six levels D) In a completely unstratified way Answer: B verified. Comment: The Internet to date, is based on the ARPA architecture consisting of 4 layers. The layers are: application, service, internetwork, network. Source: "Layered Architectures" transparencies, see also video lecture. Exercise 11. The TCP receiver A) Send cumulative feedback (ACK) B) Sends an- acknowledgement (ACK) related to each segment received C) Does not send feedback Answer: A verified. Comment: By definition TCP uses window protocols that make use of cumulative ACKs. See "TCP" transparencies. Exercise 12. The header (header) of the TCP segment, i.e., the PCI of the TCP protocol, A) It is always of fixed size equal to 20 bytes B) It is of variable size depending on the options present C) It is of fixed size equal to 40 bytes Answer: B verified. Comment: In the TCP header there is. An Options field of variable size. See "TCP" transparencies. Exercise 13. Logical addresses in the Internet are. A) Determinants completely free from the system administrators of each subnetwork B) Organized into domains C) Of completely free format Response: B verified. Comment: See transparencies on IP. Exercise 14. Between AS (Autonomous System) routing protocol can be used. A) EGP (Exterior Gateway Protocol) B) RIP (Routing Information Protocol) C) OSPF (Open Shortest Path First). Answer: A verified. Comment: Information interchange between routers belonging to different ASs is done through the EGP-type routing protocol. (Source Wikipedia) Exercise 15. In the OSI model, an (N)-connection. A) It can be realized by one or more (N-1) connections B) It is terminated by two (N-1)-CEPs.  C) Can be realized through one or more (N+1)-connections D) Can only be realized through multiple (N-1)-connections Answer: A verified. Comment: By definition, an (N)-layer provides services to (N+1)-layers. This means that its user (the N+1 layer) will have to request a connection before it can use the service. An N layer can correspond to several N-1 connections. Exercise 16. Compared with the 10Mbit/s Ethernet standard, in the definition of 100Mbit/s Ethernet, the MAC protocol A) It has been modified to enable more efficient collision detection B) It has been modified by introducing a mechanism to avoid collisions, improve performance, and support real-time services C) It was kept unchanged, accepting the reduction by a factor of ten (approximately) called "collision domain" D) It was kept unchanged, maintaining the maximum size by increasing the minimum plot size by a factor of ten Response: C verified. Comment: See transparencies on MAC. Exercise 17. The metric (cost) in a routing algorithm. A) Expresses the weight to be assigned to a (channel) link in path selection B) Expresses the computational complexity of the algorithm C) Expresses the probability that the shortest path will be used Response: A verified. Comment: see transparencies. Exercise 18. The advantages of virtual circuit type services over datagram type services in a packet-switched network are. A) Less packet delay, routing calculation for each packet B) Less variability in packet delays, maintenance of packet sequence, routing for each packet C) Less variability in packet delays, maintenance of packet sequence, routing only at connection opening phase Answer: C verified. Comment: The advantages of virtual circuit services over datagram services are: sequence retention (I always take the same route), less variability in delays (only processing delay), routing only at connection opening. See "Service over virtual circuit" transparencies. Learning Exercise 19. Which of the following statements is true about IEEE 802.1d Transparent Bridges? A) Routing follows "backward learning" and flooding criteria  B) Routing is based on the exchange of routing tables between bridges C) Routing is always done in flooding mode Answer: A verified. Comment: (Internet source). Local area network standards, p.41 Exercise 20. Compared with Fast Ethernet at 100 Mb/s (100Base T), Ethernet at 1 Gb/s allows time constraints on collision detection to be met A) Decreasing the distance between nodes B) By imposing fiber optics as the transmission medium C) Increasing the minimum size of PDUs Answer: C verified. Comment: moving to 1Gb/s to maintain Transmission Time > RTT by going to act on propagation time there would need to be minimum distances between hosts (a few tens of meters), the only solution is to increase the minimum size of PDUs so as to increase Transmission Time., By increasing the minimum size of PDUs, the time required to transmit a packet increases, allowing a greater chance of detecting and handling collisions in the network. Exercise 21. Compared with CBR (Constant Bit Rate) type sources, VBR (Variable Bit Rate) type sources. A) Have greater difference between maximum and minimum transmission speed B) They have more stringent requirements on the maximum delay C) They have more stringent requirements on average delay Answer: A verified. Comment: CBR is used in video conferencing (speed of 64kb/s). VBR is used for streaming and file transfer (for first order Mb/s to second order kb/s to Gb/s). Exercise 22. End-to-end error recovery in the Internet environment, when present, A) It is carried out always and only by the application processes B) It is carried out at the Transport (transport) level C) It is carried out at the Internet (network) level D) Not provided for any type of service Answer: B verified. Comment: End-to-end is one of the principles of computer network design and is applied on different network protocols such as in UDP(Layer 4 protocol, transport layer). (Source Wikipedia). Exercise 23. The POP3 protocol A) It is used for blocking pop-ups in a web browser B) It is used for exchanging e-mail messages between mail servers C) Can be used to transfer e-mail messages from a server to an e-mail client installed on a PC  D) Use messages that always include encrypted authentication Answer: C verified. Comment: The Post Office Protocol (POP) i s a client-server application layer protocol that is responsible for allowing a client to access an e-mail account on a host server and download e-mail from that account. B refers to the SMTP protocol. Exercise 24. What is meant by the collision domain (collision domain) in Ethernet? A) The portion of the network within which the same collision is detected B) The number of packet header bits that can be damaged by a collision C) The set of nodes that interrupt transmission due to a collision Answer: A verified. Comment: Collision domain: portion of network where two plots collide. See "Collision Domain" transparencies. Exercise 25. In an IP subnet (Logical IP Subnet). A) Hosts share the same network prefix B) The network prefix always consists of the first three bytes of the address C) Hosts always communicate by passing through the router Answer: A verified. Comment: In a network all subnets created should have the same network address. B is incorrect since the network prefix does not necessarily consist in the first 3 bytes. Exercise 26. In the OSI reference model, an (N)-PCI can contain. A) (N)-addresses B) (N+1)-addresses C) (N-1)-addresses Answer: A verified. Comment: This is the header of that level that can only contain addresses of level N. It will be the N-SDU that will contain (N+1) addresses. Exercise 27. The TCP protocol A) Provides error detection on the data of each segment using a checksum B) Provides error detection only on the segment header C) Does not provide error detection and recovery on data Answer: A verified Comment: TCP offers error-checking capabilities on received packets due to the checksum field contained in its PDU. See "TCP" transparencies (Source Wikipedia). A) Provides error detection on the data of each segment by means of a checksum. The reason behind this answer is that the TCP protocol provides error detection on each segment's data by means of a checksum. The checksum is a value calculated on the segment data, which allows detection of transmission errors or data corruption during transfer. When the recipient receives the segment, it calculates the checksum again and compares it with the received checksum value. If the values do not match, an error is assumed to have occurred during transmission. C) Does not provide error detection and recovery on data: This option is incorrect because TCP provides an error detection mechanism using the checksum. In addition, TCP also includes error recovery mechanisms such as acknowledgment and resending of lost or corrupted segments. Therefore, the correct answer is option A) Provides error detection on the data of each segment by means of a checksum. Exercise 28. The P/F(Poll/Final) bit of the plots in the LaPB layer 2 protocol. A) Provides implicit confirmation on as-yet unconfirmed storylines B) Allows you to prompt the receiver to send an acknowledgement C) Accelerates the transmission of information Answer: B verified. Comment: The Poll and Final field is one bit and has two uses. It is called Poll when used by the primary station to request a response from secondary stations, instead Final when used by a secondary station to indicate a response at the end of the transmission. It has meaning only when set to 1. (Source Wikipedia). Exercise 29. Which of the following protocols does not implement data unit boundary functions? A) LaPB (Link access Procedure Balanced), used in the ISDN B-channel B) LaPF (Link access Producer to Frame-mode bearer services), used in Frame Relay networks C) PPP (Point-to-Point Protocol), used in domestic access to the Internet D) IEEE 802.2 LLC (Logical Link Control), used in local area networks Answer: D verified. Comment: Delimiters are inserted later by the MAC protocol. See "IEEE 802.2 Logical Link Control" transparencies. Exercise 30. What is essential for Ethernet in full-duplex mode? A) The ability to simultaneously receive and transmit packets B) The availability of fault protection techniques through two disjointed paths between each pair of nodes C) Full support for both 10 Mbit/s and 100 Mbit/s speeds Answer: A verified. Comment: A full-duplex physical medium has the characteristic that transmission and reception take place over cables separated. This results in me being able to simultaneously receive and transmit packets. Exercise 31. The characteristics of a tree topology are. A) Low channel count, poor fault tolerance, easy routing B) Low channel count, good fault tolerance, easy routing C) High channel count, good fault tolerance, difficult routing Answer: A verified. Comment: See "Tree Topology" transparencies. Exercise 32. The version 4 IP addresses are: A) Of fixed total length, consisting of a variable length part identifying the network and a variable length part identifying the host B) Of fixed total length, consisting of a fixed-length part identifying the network and a fixed-length part identifying the host C) Of variable length, consisting of a variable length part identifying the network and a variable length part identifying the host Answer: A verified. Comment: IPV4 definition. See "IPV4" transparencies. Exercise 33. In Store-And-Forward packet-switched networks, the use of large PDUs (packets): A) Decreases the probability of losing information by error on received bits B) Minimizes the transfer delay because, since there is less overhead due to the control information in each PDU, the total amount of information to be sent is less C) Requires a larger header size to allow management of all the information contained in the PDU D) Increases the overall information transfer delay because each node must receive the entire PDU before it can send it on the next channel Answer: D verified. Comment: Sending large packets on Store-And-Forward type nodes leads to non-negligible delay of information transfer. For this reason, it is preferable to send small packets so as to minimize the storage (Store) time. Exercise 34. A Selective Repeat protocol with transmission window size Wt and reception window size Wr A) It can work only if, k being the number of numbering bits, we have 𝑊 + 𝑊 ≤ 2 -- Wt + Wr M1, only with traffic uniformly distributed among nodes. B) A T1 topology, with N nodes, C channels and average distance M1, always allows less traffic to be disposed of than a T2 topology, with N nodes, C channels and average distance M2>M1, regardless of the traffic distribution. C) The amount of traffic disposed in a T1 topology, with N nodes, C channels, and average distance M1, compared with that disposed in a T2 topology, with N nodes, C channels, and average distance M2>M1, depends on the distribution of traffic among nodes Answer: C verified. Comment: Given equal available channel capacity, the amount of traffic that can be disposed of by a network depends on the average distance between each pair of nodes on the network (slide: Topologies and Performance). Exercise 146. The main differences between a Frame Relay network and anetwork InternetIP include: A) The use or non-use of ARQ (automatic Retransmission reQuest) techniques in each leg of the network B) The transfer of information in connection-oriented mode instead of non-connection-oriented mode C) Transferring data units of variable size instead of fixed size Answer: B verified. Comment: Frame relay uses virtual circuit and not datagram (as IP does). Both use packets of variable size. Exercise 147. Consider an Ethernet LAN network with 10 nodes. Partition the network into two networks interconnected by transparent bridges. Which of the following statements is false? A) The bridge separates the collision domains of the two interconnected networks B) Network performance in terms of traffic disposed improves under any traffic condition, i.e., completely independent of the distribution of traffic between nodes C) Bridge introduces additional delay in transmissions between nodes connected by bridge D) It is not necessary to change the configuration of the nodes connected to the LAN to allow proper operation after the network partitioning Answer: B verified. Comment: to be determined Exercise 148. Consider two LANs (10BaSE Ethernet) A and B, connected by a bridge B1 and a router R1 (B1 and R1 are in parallel between the two LANs). Assume that the bridge and router both have active ports and know all the addresses (MAC and IP respectively) of the hosts connected to the two LANs. When a host connected to LAN A transmits an IP packet to a host connected to LAN B A) The packet is forwarded on LAN B either by the bridge or the router, depending on the value of the destination MAC address contained in the packet B) The packet is forwarded on LAN B by both router R1 and bridge B1. C) The packet is forwarded on LAN B only by router R1 D) The packet is forwarded on LAN B only from bridge B1 Response: A verified. Comment: to be determined Exercise 149. The size of the current TCP transmitter window during a connection A) It is adjusted solely on the basis of the receiver reporting the size of the receiving window to perform flow control B) Varies as congestion in the network varies and because of the flow control exerted by the receiver C) It is fixed Answer: B verified. Comment: We have that TWND