Unit 5: Transport Layer and Congestion Control - Practice Quiz

1 What is the main relationship between the transport layer and the network layer?

2 Which type of communication is primarily provided by the network layer?

3 Which transport-layer feature identifies the sending and receiving applications?

4 Which transport-layer protocol provides reliable, connection-oriented service?

5 What is multiplexing at the transport layer?

6 What does throughput measure in a computer network?

7 What is network latency?

8 Which condition commonly causes packet loss and increased delay?

9 Which TCP header field is used to place received data in the correct order?

10 What is the minimum size of a TCP header without options?

11 Which TCP header field helps detect corrupted segments?

12 How many main steps are used in the TCP connection-establishment handshake?

13 Which TCP flag is sent first when a client starts a connection?

14 What does a server normally send in the second step of the TCP three-way handshake?

15 What is the fixed size of a UDP header?

16 Which field is present in a UDP header?

17 In network-assisted congestion control, which devices provide congestion information?

18 What is the purpose of a choke packet?

19 Which TCP congestion-control phase begins with a small congestion window?

20 What does TCP usually do when a retransmission timeout indicates congestion?

21 A web browser sends data to a web server on another host. Which statement correctly describes the responsibilities of the network and transport layers?

22 Several IP packets carrying one TCP stream arrive at the destination out of order. Which layer is primarily responsible for restoring the original byte order?

23 A TCP server uses destination port 443 and simultaneously communicates with several clients. How does TCP distinguish these connections?

24 A live voice application prefers low delay and can tolerate occasional packet loss. Which transport service is most appropriate?

25 A path has a bandwidth of Mbps and a round-trip time of ms. What minimum amount of unacknowledged data is needed to approximately fill the path?

26 A TCP sender is limited to a -byte window, and the RTT is ms. Ignoring overhead and loss, what is the approximate maximum throughput?

27 A TCP segment has a Data Offset field value of . How many bytes long is its TCP header?

28 A TCP receiver has correctly received bytes numbered through . Assuming no gaps exist, what acknowledgment number should it send?

29 A TCP sender has a congestion window of bytes and receives an advertised receive window of bytes. If bytes are already unacknowledged, how much additional data may it send?

30 A TCP client sends a SYN segment with sequence number . What acknowledgment number should appear in the server's SYN-ACK?

31 A client sends SYN with sequence number , and the server responds with SYN-ACK using sequence number . Which values should the client's final ACK contain?

32 The final ACK of a TCP three-way handshake is lost. The server later retransmits its SYN-ACK. What should the client normally do?

33 The UDP Length field contains the value . How many bytes of application data are present in the datagram?

34 Why does the UDP checksum calculation include an IP pseudoheader containing source and destination IP addresses?

35 A router experiences incipient congestion and sets an ECN mark instead of dropping a packet. What is the expected end-to-end response?

36 In a choke-packet congestion-control scheme, what occurs when a router detects serious congestion?

37 A TCP sender begins slow start with a congestion window of MSS. Assuming no loss and no threshold is reached, what will the congestion window be after two complete RTTs?

38 A TCP connection is in congestion avoidance with a congestion window of MSS. After one RTT in which all segments are acknowledged, what is the approximate new window?

39 Using classic TCP behavior, a retransmission timeout occurs when the congestion window is MSS. What values are normally assigned to ssthresh and cwnd?

40 TCP Reno receives a third duplicate ACK when cwnd is MSS. Immediately after entering fast recovery, what are the usual values of ssthresh and cwnd?

41 A TCP server receives two IP packets with identical destination IP addresses and destination ports. Their source ports are also identical, but their source IP addresses differ. Assuming both packets belong to established connections, how does the transport layer demultiplex them?

42 A transport protocol runs over a network layer that may lose, duplicate, reorder, or indefinitely delay packets. Which service cannot be guaranteed solely by adding acknowledgments, sequence numbers, and retransmissions at the transport layer?

43 A bulk TCP flow uses a Mb/s path with an RTT of ms and an MSS of bytes. Its congestion window is at least the bandwidth-delay product, but its receive window is fixed at MSS. Ignoring headers and loss, what is its maximum throughput?

44 An interactive TCP application performs two small writes. After transmitting the first segment, the sender's Nagle algorithm buffers the second write because unacknowledged data exists. The receiver uses delayed ACKs and waits briefly for another segment. What is the most likely performance effect?

45 An IPv4 packet has total length bytes and IHL . Its enclosed TCP segment has Data Offset . Assuming no lower-layer padding, how many bytes of application data does the packet contain?

46 A NAT changes both the source IPv4 address and source TCP port of a segment without modifying its payload. Why must the TCP checksum normally be updated?

47 A client chooses ISN and a server chooses ISN . The client's third handshake segment acknowledges the server's SYN and carries bytes of data. What sequence and acknowledgment numbers does that segment contain, and what acknowledgment should the server return after receiving all its data?

48 Two TCP endpoints simultaneously perform active opens and send SYN segments to each other. Under standard TCP state transitions, what happens when each endpoint receives the peer's SYN while in SYN-SENT?

49 A server enables SYN cookies during a SYN flood. Which trade-off follows directly from avoiding per-connection state between receipt of SYN and receipt of the final ACK?

50 What is the maximum UDP application payload that can fit in a conventional IPv4 datagram with a -byte IPv4 header and no IPv4 options, assuming the IPv4 total-length limit is bytes?

51 A UDP datagram has a UDP Length value of bytes, so its header and data contain an odd number of octets. How is the Internet checksum computed?

52 A router experiences incipient congestion and receives an ECN-capable TCP packet. Which sequence correctly describes standard ECN feedback and reaction?

53 In an explicit-rate congestion-control scheme, a packet starts with an allowed rate of Mb/s. Three switches successively determine allowable rates of , , and Mb/s and may only reduce the rate field. What rate should be returned to the source?

54 A TCP Reno sender has MSS when it receives three duplicate ACKs. No SACK is used. What are the congestion window and slow-start threshold immediately after entering fast recovery?

55 A TCP sender's congestion window is MSS, but only MSS are outstanding when a retransmission timeout occurs. Using the rule , what values should be selected?

56 During TCP NewReno fast recovery, an ACK advances the acknowledgment number but does not cover all data outstanding when fast recovery began. How should the sender interpret this partial ACK?

57 A receiver performs an ACK-division attack by acknowledging tiny portions of a segment with many separate ACKs. Which sender behavior most directly prevents excessive congestion-window growth during slow start?

58 A sender has MSS, an advertised receive window of MSS, and MSS currently in flight. An ACK then cumulatively acknowledges MSS. If both windows are treated as unchanged for this calculation, how much new data may the sender immediately transmit?

59 Two long-lived AIMD flows have congestion windows of MSS and MSS. Between shared congestion events, both increase by the same total amount; at each event, both halve their windows. What is the difference between their windows immediately after the third such decrease?

60 Without TCP timestamps, a segment is retransmitted after timeout and an ACK later arrives that could acknowledge either the original or retransmitted copy. Under Karn's algorithm, how should the sender handle RTT estimation?