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WorksheetsNWC 101-200
Total questions: 100
Worksheet time: 51mins
Consider building a CSMA/CD network running at 1Gbps over a 1-km cable. The signal speed in the cable is 200,000 km/sec. What is the minimum frame size?
64 Bytes
640 Bytes
1250 Bytes
None of the above
In media access control, which of the following statements are true for Channelization
Inflexible in allocating bandwidth to users with different requirements
Does not scale well to large numbers of users
Widely used in internet traffic
Inefficient for bursty traffic
Time-out period is equal to maximum possible propagation delay of
Round-trip
Triangle-trip
Square-trip
Rectangle-trip
In Carrier Sense Multiple Access (CSMA), if station senses medium before trying to use it then chance of collision can be
Increased
Reduced
Doubled
Highlighted
Carrier Sense Multiple Access (CSMA) is based on medium called
Sense before transmit
Listen before sending
Listen before talk
Sense before Collision
Which of the following is not true for MAC scheduling
More efficient channel utilization
Less variability in delays
Can provide fairness to stations
Reduced computational or procedural complexity
Which of following features are typically true for local area networks?
All of the above
Low error rate
High speed
Low round-trip delay
Use HDLC and Ethernet to identify similarities between medium access control and data link control protocols. Which of following statements are true?
Both contains framing information that delineates the beginning and end of each frame.
Both check the CRC in the received frames for errors
Both implement error control and flow control for reliable transmission.
None of the above
Use IEEE 802.3 and IEEE 802.11 to discuss differences between wired and wireless LANs. Which of following statements are true about the differences?
Station mobility
Error rate
Collision detection
All of the above
Which of following is not a primary responsibility of the MAC sublayer in LANs?
Reliable connection-oriented service
Channel access
Protocol data unit addressing
Fragmentation and reassembly of MAC service data unit
In Ethernet, slot time that is at least the round-trip propagation delay, is the critical system parameter for
upper bound on time to detect collision
All of the above
upper bound on time to acquire channel
quantum for re-transmission scheduling
Which one of the following event is not possible in wireless LAN.
Acknowledgement of data frames
Collision detection
Multi-mode data transfer
Collision avoidance
In 802.11 protocol, MAC can alternate between Contention Periods (CPs) and Contention-Free Periods (CFPs)
t
f
CSMA/CD is not used in DCF because
a station is unable to listen to the channel for collisions while transmitting
physical carrier sense detects the presence of other WLAN users
in idle state, a station is unable to listen to the channel for collisions
None of the above
In infrastructure network supporting voice and data traffic, data traffic is transported through the CP and voice traffic through the CFP
t
f
In 802.11 protocol, which of the following statements are true for Basic Service Set (BSS)
Stations in BSS can communicate with each other
Multiple BSSs interconnected by Central System (CS)
Distinct collocated BSS's cannot coexist
Location in a Basic Service Area (BSA)
Consider a Gigabit Ethernet hub with stations at a 100-meter distance and average frame size of 512 bytes. Assume the propagation speed is at 2/3 of light speed. What is the value of normalized delay-bandwidth product?
0.0122
0.122
1.22
None of the above
Wireless data communication is compelling, because of
Its easy and low-cost deployment
Its support to personal and mobile devices
Its high reliability to noise and interference
All of the above
Why not use CSMA/CD in a wireless LAN? The primary reason is
The round-trip delay in a wireless LAN is too large
The frame is usually very small in a wireless LAN
The hidden station problem
All of the above
In IEEE 802.11 MAC for wireless LANs, which of following inter-frame space (IFS) is used to transmit high-priority frames such as ACKs?
SIFS
DIFS
None of the above
PIFS
Which of following statements identifies the similarity between HDLC (data link control) and Ethernet (medium access control)
All of the above
Both contain framing information that delineates the beginning and end of each frame
Both implement error control and flow control functions to provide reliable transmission
Both provide connection-oriented packet transfer services to the network layer
B
Which multiple access technique is used by IEEE 802.11 standard for wireless LAN?
ALOHA
CDMA
CSMA/CD
CSMA/CA
Which of the following are management services offered by the MAC sublayer in wireless LAN
Network management
Storage management
Roaming within ESS
Power management
In CSMA/CA, An amount of time divided into slots called
Contention window
Contention procedure
Contention energy
Contention signals
In medium access control sublayer, medium usage is mediated by the access control during contention period
t
f
In Carrier Sense Multiple Access/Collision Detection (CSMA/CD), to continue transmission process we use a
Signal
Station
Access point
Loop
Which layer LAN bridges work on?
Transport layer
Network layer
Medium access control
None of above
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?
repeaters
routers
bridges
All of the above
Of the following network layer functions, which one is optional?
Routing
Forwarding
Congestion control
None of the above
Of the following, which is a basic function of transparent bridge?
All of the above
Learns where stations are attached to the LAN
Prevents loops in the topology
Forwards frames from one LAN to another
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
All of the above
connection-oriented transfer of packets with delay guarantee
Best-effort connectionless service
connection-oriented reliable stream service
The network layer is considered the most complex layer because of the following reasons
Requires coordinated actions of multiple, geographically distributed network elements
Responsible for displaying received information to users
Challenges such as addressing and routing
User scalability
An end-to-end function is best implemented at a lower level than at a higher level
t
f
Which of the following is an essential network function
Forwarding
Routing
Priority and scheduling
All of the above
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
The main purpose of access multiplexer is to combine the typically bursty traffic flows from the individual computers into aggregate flows
t
f
Which of the following functions can a home router perform?
Private IP addresses in home by network address translation
All of the above
Local area network access using WiFi
Single global IP address using DHCP
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
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
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
Packet pipelining can lead to latency in message delivery
t
f
In internet, switching is done by using datagram approach to packet switching at the
Data link layer
Application layer
Physical layer
Network layer
A transparent bridge's duties include
Forwarding
Blocking
Filtering frame
All of the above
For a 10Mbps Ethernet link, if the length of the packet is 32bits, the transmission delay is(in microseconds)
0.32
320
3.2
32
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
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
Which of following issue exists in virtual-circuit subnet but not in datagram subnet?
Addressing
State information
Routing
None of the above
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
Which of following describe benefits of flooding, a specialized routing approach?
No routing table needed for routers
Useful in propagating information to all nodes
All of the above
Always reach the destination by the fastest path
A Virtual-Circuit Network (VCN) is normally implemented in the
session layer
data link layer
network layer
Physical layer
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
To reduce size of routing table, routers do lookup table on MAC address
t
f
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
What are possible metrics for routing?
Hop count
Delay
Bandwidth
All of the above
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
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
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
In a virtual-circuit packet network, routing is determined during connection set-up
t
f
In deflection routing, bufferless operation is considered a disadvantage due to packet loss
t
f
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
The simplest approach to queue scheduling is First-In, First-out queueing, where all packet flow make use of different buffer
True
False
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
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
In buffer management, drop priorities requires packet to drop when buffer is full
t
f
What are the key mechanisms in Open-Loop Control
Traffic shaping
Admission control
Re-routing
Policing
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
To guarantee network performance during the lifetime of admitted flows, open-loop control relies on the following mechanism except:
Head-of-Line queueing
Traffic shaping
Traffic policing
Admission control
Which of following statements about leaky bucket is wrong?
. In leaky bucket, when the bucket is full, the new arriving packets may be discarded
Leaky bucket is a flow-level traffic management mechanism
In the leaky bucket, the packet output rate can be variable
In the leaky bucket, the packet output rate is always constant
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
Upon which of the following condition is token bucket and leaky bucket the same?
Leaky bucket size is zero
Token bucket size is infinite
Leaky bucket size is infinite
Token bucket size is zero
In Head of Line (HOL) priority queueing, which of the following statement is true for this approach
High priority queue has higher waiting time
Buffers can be dimensioned for different loss probabilities
High priority queue has lower waiting time
High priority queue services until empty
In buffer management, which feature requires packet to drop when buffer is full
Drop priorities
Fairness
Drop strategy
Aggregation
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
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
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
Which of the following protocols work at IP layer?
ICMP
ARP
IGMP
All of the above
Which of the following packet header length cannot be used in an IPv4 packet header?
20 Bytes
. 30 Bytes
60 Bytes
64 Bytes
How many bits used for header checksum in IPv4 packets?
8 bits
16 bits
32 bits
None of the above
What is the dotted notation of an IP address of 10000000 10000111 01000100 00000101 ?
128.135.65.5
128.135.65.5
128.135.68.5
128.133.68.5
Given a network address 128.100.0.0, what is its network class type?
Class A
Class B
Class C
None of the above
What is the root problem of link state routing?
Counting to infinity
Flooding overhead
Slow reaction to link failures
All of the above
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
Which of following is the implementation of distance vector approach in the IP routing protocol?
RIP
OSPF
BGP
None of the above
A
Which of following is the implementation of link state approach in the IP routing protocol?
RIP
OSPF
BGP
None of the above
In Routing Information Protocol (RIP), the use of max number limited to 15 limits the count-to-infinity problem
t
f
In an OSPF network, routers in area only knows complete topology inside area and limits the flooding of link-state information to area
t
f
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
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
In Asynchronous Transfer Mode (ATM), the packet structure attribute simplifies implementation and ensures high speed transfer
t
f
Which of the following features are true for asynchronous transfer mode (ATM)?
It supports quality of service
All of the above
It only supports fixed-length packets
It is connection-oriented
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 routerexpects an update from each of its neighbors within 180 sec
Convergence speed up by triggered updates
All of the above
What are the limitations of RIP protocol
Limited metric use
Slow convergence
Fixed number of hops
Update message overhead
In Open Shortest Path First (OSPF), which of the following statements are correct
Enables each router to learn complete network topology
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
Which of the following is a type of router defined in OSPF
. Internal router
Area border router
Backbone router
All of the above
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
Based on traffic granularity, which of the following levels is traffic management not usually classified into?
Flow level
Byte level
Flow-aggregated level
Packet level
Which of following statements is true for FIFO queueing?
In FIFO queueing, all packet flows share the same buffer
FIFO queueing cannot provide differentiated QoS to packet flows
All of the above
In FIFO queueing, arriving packets will be discarded if the buffer is full
Which of following is not a packet-level mechanism?
Fair queueing
Token bucket shaping
Head-of-line priority queueing
Random early detection
What are typical end-to-end Quality-of-Service factors?
Jitter
Packet delay
Packet loss rate
All of the above
By Random Early Detection (RED), when a given source transmits at a higher rate than others, the source will
Achieves a higher bandwidth
Suffers a higher packet-dropping rate
Achieves a lower waiting delay
Suffers a lower packet-dropping rate
