CS417 Exam 1

Fall 2012

Paul Krzyzanowski

    Part I – 16 points

  1. 4 points
    How did CIDR (classless inter-domain routing) alleviate the problem of running out of IP addresses?
  2. 4 points
    Explain how each of the following contributes to latency.
    (a) Packet aggregation
    (b) Packet loss
  3. 4 points
    What is the security problem with ARP (Address Resolution Protocol)?
  4. 4 points
    (a) You send a time sync request at 2:30:15.200. You get a response at 2:30:15.400. The response contains a time stamp of 2:30:15.100. To what value do you set your clock using Cristian’s algorithm?
    (b) If the best-case round-trip delay is 0.050 seconds, what is the error of the synchronization? Express your answer as ±E, where E is a number in milliseconds (1000 milliseconds = 1 second).

    5. Part II – 55 points – 3 points each

    For each statement, select the most appropriate answer. You may omit one question. Please indicate your choice clearly.

  5. A snoopy cache in an SMP (symmetric multiprocessor) architecture requires that all of a CPU’s memory operations be:
    (a) Read-through.
    (b) Write-through.
    (c) Both read-through and write-through.
    (d) Completely isolated from the system bus.
  6. A single system image is:
    (a) An OS installation that is targeted to just one system.
    (b) An OS installation that can be deployed onto multiple systems to create a distributed environment.
    (c) Software that makes a collection of computers appear as one system.
    (d) A sump of the memory of a computer system.
  7. Unlike UDP, sending data over TCP will
    (a) Use less bandwidth.
    (b) Ensure data delivery with low jitter.
    (c) Provide reliable data delivery.
    (d) Span multiple physical networks.
  8. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)
    (a) Uses TDMA (time division multiple access) to avoid collisions.
    (b) Is designed for circuit-switched networks while CSMA/CD is designed for packet switched networks.
    (c) Is designed for network environments that cannot detect collisions, such as wireless.
    (d) Schedules packet transmission in a way that collisions cannot occur.
  9. Which of the following is not a field in an IPv4 header?
    (a) Source address.
    (b) Time to live.
    (c) Header checksum.
    (d) Destination port.
  10. Which system call is unnecessary for UDP communication?
    (a) socket
    (b) bind
    (c) accept
    (d) sendto
  11. Routing between different local area networks is part of this layer:
    (a) Physical (1).
    (b) Data link (2).
    (c) Network (3).
    (d) Transport (4).
  12. Weighted Fair Queuing:
    (a) Allows for packet prioritization but risks starvation, where some packets may be delayed indefinitely.
    (b) Allows for packet prioritization without starvation.
    (c) Gives each packet queue in a router equal priority.
    (d) Sends larger packets out first to reduce congestion.
  13. A leaky bucket improves:
    (a) Average bandwidth.
    (b) Latency.
    (c) Jitter.
    (d) Packet loss.
  14. A token bucket is a way of controlling:
    (a) Average bandwidth.
    (b) Latency.
    (c) Jitter.
    (d) Packet loss.
  15. DiffServ is an example of
    (a) Flow detection.
    (b) Traffic classification.
    (c) Hard QoS.
    (d) Admission control.
  16. A key distinction between IntServ (integrated services) and DiffServ (differentiated services) is:
    (a) Integrated services are a set of services provided by the operating system.
    (b) Integrated services support admission control.
    (c) Integrated services get a higher priority on routers than differentiated services.
    (d) Integrated services are a set of services running directly on routers.
  17. The role of the master differs between the Berkeley synchronization algorithm and PTP because:
    (a) The PTP (Precision Time Protocol) algorithm achieves more precise synchronization.
    (b) The goal of the Berkeley algorithm is for all nodes to end up with the same time.
    (c) The master initiates the synchronization under the Berkeley algorithm.
    (d) The master in the Berkeley algorithm may not have the definitive time.
  18. An NTP server is assigned a stratum based on:
    (a) How indirectly it synchronizes with a master time source.
    (b) How recently it synchronized its clock.
    (c) How accurate the server’s clock is over time.
    (d) How many clients synchronize with it.
  19. Which event causally precedes an event with the timestamp of (3, 7, 4)?
    (a) (1, 1, 5)
    (b) (3, 8, 4)
    (c) (2, 7, 5)
    (d) (2, 6, 4)
  20. In a reliable multicast:
    (a) Messages are guaranteed to arrive in the order that they were sent.
    (b) Messages are guaranteed to eventually arrive at all destinations.
    (c) Messages cannot be retransmitted.
    (d) Messages may fail to arrive at some destinations if the sender dies while transmitting.
  21. An Ethernet controller cannot accept multicast packets via
    (a) Matching a hash of the address.
    (b) Matching the address against a set of addresses.
    (c) Multicast promiscuous mode.
    (d) A subscription request.
  22. A benefit of IGMP v3 over earlier versions is:
    (a) You can specify the source address of a sender in the multicast group you want to join.
    (b) You can explicitly send a leave message to unsubscribe from a group.
    (c) The protocol is more network efficient since it does not use flooding.
    (d) A coordinator keeps track of group membership.
  23. A client stub in an RPC system:
    (a) Locates the remote server.
    (b) Initializes the RPC subsystem.
    (c) Marshals function parameters into a network message.
    (d) Contains the main program that listens for connections from servers.

    24. Part III – 30 points, 2 points each

    For each statement, specify whether it is true or false by circling the correct choice. You may omit one question. Please indicate your choice clearly.

  24. A snoopy cache results in a reduction in memory write operations on the system bus.
    [True] [False]
  25. Memory access in a NUMA (Non-Uniform Memory Access) architecture is called non-uniform because it is slower during times when two processors access the same region of memory.
    [True] [False]
  26. Ethernet is an example of a circuit switched network that uses TDMA.
    [True] [False]
  27. A switched network interconnect allows additional hosts to be added without decreasing available bandwidth on the LAN.
    [True] [False]
  28. Datagram delivery is expected to be in-order but unreliable.
    [True] [False]
  29. It is possible to derive a machine’s IP address from its Ethernet address.
    [True] [False]
  30. TCP is a layer on top of UDP that provides reliable communication.
    [True] [False]
  31. Admission control restricts which packets a router will accept.
    [True] [False]
  32. A choke packet is a large packet that delays the routing of other packets.
    [True] [False]
  33. Flows are automatically detected while classes are defined by administrators.
    [True] [False]
  34. Converting a bursty flow of data into a smooth flow is an example of traffic policing.
    [True] [False]
  35. ATM differs from IP in that a fixed route is set up at the time that a connection is established.
    [True] [False]
  36. An IP domain name is an example of a compound name.
    [True] [False]
  37. If event a causally precedes event b then the Lamport timestamp of a is always less than that of b.
    [True] [False]
  38. If the Lamport timestamp of event a is less than that of b then event a always causally precedes event b.
    [True] [False]
  39. In PIM sparse mode multicast, the multicast streams are initiated by receivers rather than senders.
    [True] [False]
Last modified March 24, 2020.

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