Packet Switching Networks and Algorithms Coursera Quiz Answers

All Weeks Packet Switching Networks and Algorithms Coursera Quiz Answers

Packet Switching Networks and Algorithms Week 01 Quiz Answers

Practice Assessment – Frame Switching and Packet Switching

Q1. Which layer LAN bridges work on?

• Transport layer
• Network layer
• Medium access control
• None of above

Q2. One can use repeaters, bridges and routers to interconnect two LANs. Which of the following approaches will make local traffic stay in its own LAN?

• routers
• repeaters
• All of the above
• bridges

Q3. Of the following network layer functions, which one is optional?

• Routing
• Forwarding
• Congestion control
• None of the above

Q4. Of the following, which is a basic function of transparent bridge?

• Prevents loops in the topology
• All of the above
• Forwards frames from one LAN to another
• Learns where stations are attached to the LAN

Q5. It is possible for a network layer to provide a choice of services to the user of the network. Which of following the IP network layer offers

• Best-effort connectionless service
• All of the above
• connection-oriented reliable stream service
• connection-oriented transfer of packets with delay guarantee

Q6. The network layer is considered the most complex layer because of the following reasons

• User scalability
• Responsible for displaying received information to users
• Requires coordinated actions of multiple, geographically distributed network elements
• Challenges such as addressing and routing

Q7. An end-to-end function is best implemented at a lower level than at a higher level

• True
• False

Q8. Which of the following is an essential network function

• Forwarding
• Routing
• Priority and scheduling
• All of the above

Q9. In network layer, which of the following statement is true for packet networks

• Individual packet streams are highly bursty
• User demand can undergo dramatic change
• Internet structure is highly decentralized
• All of the above

Q10. The main purpose of access multiplexer is to combine the typically bursty traffic flows from the individual computers into aggregate flows

• True
• False

Graded Assessment – Frame Switching and Packet Switching

Q1. Which of the following functions can a home router perform?

• Local area network access using WiFi
• Private IP addresses in home by network address translation
• Single global IP address using DHCP
• All of the above

Q2. Consider a three hop network from the source to the destination. Let m be the packet transmission time at each hop. Let n be the propagation delay at each hop. Assume there is no queuing delay and processing time at each hop. Based on store-and-forward, what is the total time for the packet to be transmitted to the destination?

• m + n
• 3m + n
• 3m + 3n
• None of the above

Q3. Consider a three hop network from the source to the destination. Let m be the message transmission time at each hop. Let n be the propagation delay of each hop. Assume there is no queueing delay and processing time at each hop. Based on store-and-forward, what is the total time for three packets to be transmitted to the destination by packet pipelining?

• 3m + 3n
• 5m + 3n
• 9m + 9n
• None of the above

Q4. Six stations (S1-S6) are connected to an extended LAN through transparent bridges (B1 and B2), as shown in the following figure. Initially, the forwarding tables are empty. Both bridges use backward learning to build their tables. Suppose station S2 transmits a frame to S1. Which of following statements is correct?

• The frame will reach bridge B2 only
• None of the above
• The frame will reach bridge B1 only
• The frame will reach both bridges B1 and B2

Q5. Following the above question. Suppose stations S 3 transmits a frame to S5. Which of following statements is correct?

• The frame will reach bridge B1 only
• The frame will reach bridge B2 only
• The frame will reach both bridges B1 and B2
• None of the above

Q6. One can use repeaters, bridges and routers to interconnect two LANs. Which of the following approaches will make local traffic appear in both LANs?

• Repeater
• Routers
• Bridges
• All of the above

Q7. Packet pipelining can lead to latency in message delivery

• True
• False

Q8. In internet, switching is done by using datagram approach to packet switching at the

• Network layer
• Application layer
• Physical layer
• Data link layer

Q9. A transparent bridge’s duties include

• Forwarding
• Blocking
• Filtering frame
• All of the above

Q10. For a 10Mbps Ethernet link, if the length of the packet is 32bits, the transmission delay is(in microseconds)

• 3.2
• 0.32
• 320
• 32

Packet Switching Networks and Algorithms Week 02 Quiz Answers

Practice Assessment – Routing in Packet Networks

Q1. Which of following networks represents an example of virtual circuit switching at the network layer?

• IP
• ATM
• Both of the above
• All of the above

Q2. Consider a three hop network from the source to the destination. Let m be the message transmission time at each hop. Let n be the propagation delay of each hop. Assume there is no queueing delay and processing time at each hop. Based on cut-through switching, what is the total time for three packets to be transmitted to the destination?

• 3m + 3n
• 5m + 3n
• 9m + 9n
• None of the above

Q3. Which of following issue exists in virtual-circuit subnet but not in datagram subnet?

• Addressing
• State information
• Routing
• None of the above

Q4. Which of following describe general goals in a routing algorithm?

• Rapid responsiveness to network changes
• Robustness under high load and link failure
• Low overhead for implementation
• All of the above

Q5. Which of following describe benefits of flooding, a specialized routing approach?

• Useful in propagating information to all nodes
• No routing table needed for routers
• All of the above
• Always reach the destination by the fastest path

Q6. A Virtual-Circuit Network (VCN) is normally implemented in the

• session layer
• data link layer
• network layer
• Physical layer

Q7. In routing approaches, which of the following statement is true for deflection routing

• Fixed, preset routing procedures
• No route synthesis
• Useful in starting up network
• Predefined source to destination route

Q8. To reduce size of routing table, routers do lookup table on MAC address

• True
• False

Graded Assessment – Routing in Packet Networks

Q1. Flooding may easily swamp the network as one packet creates multiple packets, possibly in exponential growth rate. What are possible means to reduce resource consumption in the network?

• Use a time-to-live field in each packet to limit its lifetime
• Add a unique identifier to a packet for removing its duplicate
• Use address and sequence number to discard duplicates
• All of the above

Q2. What are possible metrics for routing?

• Hop count
• Delay
• Bandwidth
• All of the above

Q3. Consider the network as shown in the figure. We use the Bellman-Ford algorithm to find the set of shortest paths from all nodes to the destination node 2. Each node maintains an entry (n, cost) about the next node along the current shortest path and the current minimum cost from the node to the destination. Initially, each node has entry (-1, infinity).

In the first algorithm iteration, which nodes will update their entries and inform their neighbors?

• 1
• 4
• 5
• All of the above

Q4. Following the above question, in the second algorithm iteration, which nodes will update their entries and inform their neighbors?

• 3
• 4
• 6
• All of the above

Q5. Following the above question, in the third algorithm iteration, which nodes will update their entries and inform their neighbors?

• 3
• 4
• 6
• All of the above

Q6. In link state routing, after the construction of link state packets new routes are computed using

• Dijkstra’s algorithm
• Bellman Ford algorithm
• Leaky bucket algorithm
• None of the above

Q7. A subset of a network that includes all the routers but contains no loops is called

• Broadcast structure
• spanning tree
• Multi-destination routing structure
• None of the above

Q8. In a router, which of the following statement is true for creating routing tables

• Need information on state of links
• Need to distribute link state information using a routing protocol
• Need to compute routes based on information
• All of the above

Q9. In a virtual-circuit packet network, routing is determined during connection set-up

• True
• False

Q10. In deflection routing, bufferless operation is considered a disadvantage due to packet loss

• True
• False

Packet Switching Networks and Algorithms Week 03 Quiz Answers

Practice Assessment – Shortest-Path Routing

Q1. What is the root problem of Bellman-Ford algorithm for distance vector approach?

• Counting to infinity
• Flooding overhead
• Cannot work in IP
• All of the above

Q2. What is the root problem of link state routing?

• Counting to infinity
• Flooding overhead
• Slow reaction to link failures
• All of the above

Q3. Which of following describe the benefits of link state routing compared to distance vector routing?

• Fast convergence
• Support for multiple metrics
• Support for multiple paths to a destination
• All of the above

Q4. Which of following is the implementation of distance vector approach in the IP routing protocol?

• RIP
• OSPF
• BGP
• None of the above

Q5. Which of following is the implementation of link state approach in the IP routing protocol?

• RIP
• OSPF
• BGP
• None of the above

Q6. In Routing Information Protocol (RIP), the use of max number limited to 15 limits the count-to-infinity problem

• True
• False

Q7. In an OSPF network, routers in area only knows complete topology inside area and limits the flooding of link-state information to area

• True
• False

Q8. In link state routing, which of the following are possible steps taken to resolve the problem of old update messages

• Add time stamp to each update message
• Add sequence number to each update message
• Add a null number to each update message
• None of the above

Q9. In Asynchronous Transfer Mode (ATM), which of the following is an examples of supported services

• Real time voice and video
• Circuit emulation for digital transport
• Data traffic with bandwidth guarantees
• All of the above

Q10. In Asynchronous Transfer Mode (ATM), the packet structure attribute simplifies implementation and ensures high speed transfer

• True
• False

Graded Assessment – Shortest-Path Routing

Q1. Which of the following features are true for asynchronous transfer mode (ATM)?

• All of the above
• It only supports fixed-length packets
• It is connection-oriented
• It supports quality of service

Q2. Consider the network as shown in the figure. We use the Dijkstra’s algorithm to find the set of shortest paths from all nodes to the destination node 4. In Dijkstra’s algorithm, each iteration the next closet node is added to the set with the root node.

At the first iteration, which node will be added to the set N?

• 2
• 3
• 1
• 5

Q3. Following the question above, at the second iteration, which node will be added to the set N?

• 5
• 3
• 1
• 6

Q4. Following the question above, at the third iteration, which node will be added to the set N?

• 3
• 6
• 5
• 1

Q5. Following the question above, at the fourth iteration, which node will be added to the set N?

• 6
• 1
• 3
• 5

Q6. In RIP operation, which of the following statement is correct

• Router sends update message to neighbors every 30 sec
• To deal with changes in topology such as a link failure, a router expects an update from each of its neighbors within 180 sec
• Convergence speed up by triggered updates
• All of the above

Q7. What are the limitations of RIP protocol

• Limited metric use
• Slow convergence
• Fixed number of hops
• Update message overhead

Q8. In Open Shortest Path First (OSPF), which of the following statements are correct

• OSPF typically converges slower than RIp when there is a failure in the network
• Allows routers to build shortest path tree with router as root
• Each router builds an identical link-state database
• Enables each router to learn complete network topology

Q9. Which of the following is a type of router defined in OSPF

• Internal router
• Area border router
• Backbone router
• All of the above

Q10. In a distance vector routing, if a link fails

• All routers immediately update their link database and recalculate their shortest path
• Neighboring routers exchange routing tables that may use failed links
• Routers set link distance to infinity and floods the network with an update packet
• All of the above

Packet Switching Networks and Algorithms Week 04 Quiz Answers

Practice Assessment – Traffic Management

Q1. Based on traffic granularity, which of the following levels is traffic management not usually classified into?

• Flow-aggregated level
• Byte level
• Flow level
• Packet level

Q2. Which of following statements is true for FIFO queueing?

• All of the above
• In FIFO queueing, all packet flows share the same buffer
• FIFO queueing cannot provide differentiated QoS to packet flows
• In FIFO queueing, arriving packets will be discarded if the buffer is full

Q3. Which of following is not a packet-level mechanism?

• Fair queueing
• Head-of-line priority queueing
• Random early detection
• Token bucket shaping

Q4. What are typical end-to-end Quality-of-Service factors?

• Jitter
• Packet delay
• Packet loss rate
• All of the above

Q5. By Random Early Detection (RED), when a given source transmits at a higher rate than others, the source will

• Achieves a higher bandwidth
• Achieves a lower waiting delay
• Suffers a higher packet-dropping rate
• Suffers a lower packet-dropping rate

Q6. The simplest approach to queue scheduling is First-In, First-out queueing, where all packet flow make use of different buffer

• True
• False

Q7. In FIFO queueing, delay and loss of packets depends on _________ and _________

• Packet size, sequence number
• inter-arrival, packet lengths
• routing path, sequence number
• RTT value, packet lengths

Q8. Which of the following is a feature of fair queueing

• Every user flows share the same logical buffer
• Idealized system assumes fluid flow from queues
• Addresses different users by order or request
• None of the above

Q9. In buffer management, drop priorities requires packet to drop when buffer is full

• True
• False

Q10. What are the key mechanisms in Open-Loop Control

• Traffic shaping
• Admission control
• Re-routing
• Policing

Graded Assessment – Traffic Management

Q1. Which of the following statements is wrong about fair queuing?

• Fair queueing is a packet-level traffic management
• Fair queueing attempts to provide equal-size buffers to flows
• Fair queueing attempts to provide equitable access to transmission bandwidth
• All of the above

Q2. To guarantee network performance during the lifetime of admitted flows, open-loop control relies on the following mechanism except:

• Traffic policing
• Admission control
• Traffic shaping
• Head-of-Line queueing

Q3. Which of following statements about leaky bucket is wrong?

• In the leaky bucket, the packet output rate can be variable
• In the leaky bucket, the packet output rate is always constant
• Leaky bucket is a flow-level traffic management mechanism
• In leaky bucket, when the bucket is full, the new arriving packets may be discarded

Q4. Consider a token bucket approach for traffic shaping. A token is generated every 5 micro-seconds. Each packet can hold 48 bytes of data. What is the sustainable data transmission rate by the token bucket?

• 7.68 Mbps
• 76.8 Mbps
• 768 Mbps
• None of the above

Q5. Upon which of the following condition is token bucket and leaky bucket the same?

• Token bucket size is infinite
• Leaky bucket size is zero
• Token bucket size is zero
• Leaky bucket size is infinite

Q6. In Head of Line (HOL) priority queueing, which of the following statement is true for this approach

• Buffers can be dimensioned for different loss probabilities
• High priority queue has higher waiting time
• High priority queue services until empty
• High priority queue has lower waiting time

Q7. In buffer management, which feature requires packet to drop when buffer is full

• Aggregation
• Drop strategy
• Drop priorities
• Fairness

Q8. In buffer management, which of the following statement is correct for Random Early Detection (RED) technique

• Improves performance of cooperating TCP sources
• Reduce loss probability of misbehaving sources
• Packets produced by TCP will reduce input rate in response to network congestion
• Early drop causes some sources to reduce rate before others, causing gradual reduction in in aggregate input rate

Q9. In Closed-Loop flow control, which of the following mechanism is used in congestion control to regulate the flow from sources into network

• Buffer length
• Link utilization
• Packet header size
• Round-Trip Time

Q10. In congestion warning, the feedback mechanism can be implicit or explicit. Which of the following is an example of implicit feedback

• A time-out due to missing acknowledgement
• The warning bit in ACKs
• Choke packets to the source
• None of the above

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