WorksheetsPacket Switching
Total questions: 99
Worksheet time: 55mins
For packet-switched networks: Which of the following statements are correct?
Data is transferred in small packets with a maximum length of 1000 B
Data is transferred in small packets with a minimum length of 500 B
If the source has a message shorter than 500 B, it sends it in a single packet
If the source has a message longer than 8000 B, it sends it in a single packet
One packet contains user data and another, sent immediately after it, contains control data
Which of the following are advantages of packet-switched networks?
Constant data transfer rate
Synchronized time-division use of the channel between two nodes
If it is necessary to equalize the data transfer rates between two stations, the packet is discarded and resent when the receiver is ready
Packets are queued and forwarded as fast as possible
All packets have the same priority when being sent
To manage packets through the network, two approaches are used: datagram and virtual circuits. Each is characterized by:
In the datagram approach, each packet is treated independently of packets sent before it
In virtual circuits, the path along which the packet will be delivered is determined before the packet is sent
In virtual circuits, all packets have the same destination address
In the datagram approach, all packets of a message must arrive in the order they were sent
Each packet in a datagram network has an identifier
Which relations are correctly defined when comparing the datagram approach and virtual-circuit approach?
The packet transfer time is smaller in the datagram approach
With datagrams, short messages are transferred faster
The datagram approach is more secure than the virtual-circuit approach
If two stations exchange data for a long time, the virtual-circuit approach is more effective
The number of packets sent is the same for both approaches
Which performance parameters of a network are correctly defined?
Transmission time – the time needed for the signal to go from one node to another
Propagation time – the time needed for the sender to transmit a block of data
Transmission time – time needed for the signal to be transmitted through all nodes along the path
Propagation time – time needed for the packet to go from the source to the next node on the path
Node delay – the time needed to process the data in the node before it is forwarded
How many functionally different services does a packet-switched network provide?
2
3
4
5
6
Packet routing is one of the most complex and important aspects of packet-switched networks. It must satisfy:
Robustness
Optimality
Stability
Reliability
Effectiveness
The place of decision defines which node(s) are responsible for routing decisions. It can be:
centralized
at the receiver
at the sender
distributed
at the first neighbor node of the source
Which of the following are routing strategies in packet-switched networks?
Adaptive
Fixed
Flooding
Alternative
Random
In packet-switched networks, for flooding routing it holds that:
At each node, the packet is forwarded to all neighboring nodes
The packet is sent from the sender to two of its neighboring nodes
The path with minimum cost will be used by at least one copy of the packet that reaches the receiver
If there is a path between sender and receiver, the sent packet will definitely arrive at the receiver
To avoid congestion due to flooding, a counter is introduced that is increased at each hop
Packet transmission is designed as an architecture that:
Uses lines more efficiently than circuit switching
Performs data transfer in small blocks called packets
Sends data in packets
Packets consist only of user data
Packets consist of user data plus control information
A network that uses a packet-switching architecture:
Does guarantee reliable delivery of data
Does guarantee reliable delivery of packets
Does not guarantee reliable delivery of packets
Is a best-effort network
When a packet-switched network becomes overloaded:
It blocks all connections
It stops accepting new packets
Packets may be discarded
Packet delay increases
When a node receives a message larger than the maximum packet size:
It reports an error
It segments the message into smaller parts and sends them sequentially
It sends only part of the message up to the maximum packet size
When a station has a message larger than the maximum packet size and splits it into smaller packets and sends them sequentially:
All packets must follow the same path
All packets may follow the same path
Each packet is routed independently
In communication with virtual circuits:
All packets follow the same path
Not all packets must follow the same path
Each packet is routed independently
The main characteristic of the virtual-circuit technique is that:
All packets must follow the same path
The path is established in advance for all packets
All connections have a fixed path
A path is pre-established for all possible connections
What is a connection-oriented service?
A mode of packet transfer in which the path is set up in advance
A mode of packet transfer in which the path is not set up in advance
In it, all packets travel along the same path
In a connection-oriented service, the logical connection is called:
virtual connection
virtual circuit
virtual packet connection
When packet transfer is based on a connectionless service:
The network forwards each packet independently
The network does not guarantee reliable delivery
The network guarantees reliable delivery
The network does not guarantee in-order delivery
In packet switching:
The utilization of communication lines is higher than in circuit switching
The utilization of communication lines is lower than in circuit switching
The line can be used only by two nodes at the same time
TDM (Time Division Multiplexing) is used
The sending rate in packet switching:
How many functionally different combinations of services does a packet-switched network provide?
Four
Two
Six
Eight
Which statement correctly describes external virtual circuit, internal virtual circuit operation?
There is a dedicated virtual path between the stations and every packet is sent along it
Different packets for the same external virtual circuit can be transferred along different internal paths
Every packet is treated independently by both the user and the network
From outside the user sees no connection, they just send packets one by one
Which statement correctly describes external datagram, internal datagram operation?
There is a dedicated virtual path between the stations and every packet is sent along it
Each packet is treated independently, both by the user and by the network
The network sets up logical connections between the stations
Each packet is treated depending on (tied to) both the user and the network
The time and place where the decision is made about which path packets will follow can be:
At the beginning and end of the network
At the beginning, when a virtual circuit is established, if the internal transfer is via virtual circuit
At the moment when the packet arrives at a node
The time of packet arrival at a node is predetermined in advance
Based on the information a node receives, it runs an algorithm to find the minimum-cost path. Which algorithms are most commonly used?
Dijkstra’s algorithm
Jacobson’s algorithm
Bellman–Ford algorithm
ARPANET algorithm
What are the two functions of a routing protocol?
Defines the format and use of the fields in the packet
Enables sharing of path (route) information
Communicates with other routers
Provides MAC address information so the router can send data over a WAN
Determines the OUI
Decisions about routing are most often based on which parameters?
Network topology
Traffic load (traffic density)
Packet priority
Data format
Link speed
The timing of routing-information updates is a function of:
The source of the information
The routing strategy
The receiver of the information
The network topology
Which techniques are routing strategies?
Adaptive routing
Fixed routing
Flooding (routing with flooding)
Variable routing
Random routing
Which routing techniques are most often used by packet-switched networks?
Fixed routing
Variable routing
Routing with virtual circuits
Random routing
Adaptive routing
In adaptive routing, the information source can be:
Local (at the node itself)
Contained inside the packets
In neighboring nodes
In all nodes
What best describes path selection at the network layer?
The router uses a routed protocol to choose the best path for data transmission. The router uses a routing protocol to compare LAN equipment through which to send data. The switch compares information from the routing table to choose the best path. Which statement is correct?
The router uses a routed protocol to choose the best path for data transmission
The router compares information from the routing table to choose the best path
The router uses a routing protocol to compare LAN equipment through which to send data
The switch compares information from the routing table to choose the best path
Which protocol is used to eliminate loops?
STP (Spanning Tree Protocol)
BDPU
UDP
EIGRP
learning
What best describes the Spanning Tree Protocol?
It allows the switch to eliminate switching loops
It allows the switch to dynamically choose the best switch mode
It allows the switch to behave as a router
The ATM protocol model consists of which parts?
User (user plane)
Control (control plane)
Management (management plane)
Information
Supervisory
Which statements are true for ATM logical connections?
A virtual path is a set of virtual channels that have the same two endpoints
Virtual path is the basic switching unit in an ATM network
To set up a virtual channel, there must first exist a virtual path to the destination node with enough capacity and appropriate quality of service
Data through a virtual channel is always transferred at a constant bit rate
A virtual channel is established between two end users of the network
When traffic parameters are negotiated, agreement must be reached on:
Average bit rate
Peak (maximum) bit rate
Minimum bit rate
Cell delay
Possible control mechanisms for a virtual path are:
Semi-permanent
User-controlled
Network-controlled
Meta-signaling based
Controlled by a central node
Which statements are true for an ATM cell?
Each cell has a minimum length of 53 octets
Each cell has a 5-octet header and a 48-octet payload field
All cells have the same priority
The cell header contains the virtual path and virtual channel identifiers
VCI determines the routing field for the network
Which data rates are supported for ATM cells?
622.08 Mbps
155.52 Mbps
52.84 Mbps
25.6 Mbps
1.044 Mbps
Mark the non–real-time services provided by ATM:
Non–real-time Variable Bit Rate (nrt-VBR)
Available Bit Rate (ABR)
Unspecified Bit Rate (UBR)
Constant Bit Rate (CBR)
Real-time Variable Bit Rate (rt-VBR)
The adaptation layer (AAL) in the ATM model consists of which logical sublayers?
Convergence sublayer
Segmentation and Reassembly (SAR) sublayer
Transmission-control sublayer
Compared to X.25, frame-based exchange (frame relay) is characterized by:
Shared logical links for control and user data
Implementation of flow control on each node-to-node link
Multiplexing and switching of logical links is done at layer 3
Control signaling is placed on a different logical link from the user data
No error control on each node-to-node link
Virtual channels established between end users are used for:
Transfer of user data and control signals from one end to the other
Transfer of network-information between users
Network management
Transfer of data between intermediate nodes
When a virtual channel is established between a user and a network entity, it is used for:
Transfer of control signals between the user and the network
Accumulation of the traffic from exchanges between the user and the network or from a network server
Management of network traffic
Transfer of user data and control signals from one end to the other
When a virtual channel is established between network entities, it is used for:
Network-traffic management
Routing
Transfer of control signals between network entities
Transfer of control signals
Which statements are true for ATM logical connections?
Virtual path is the basic switching unit in an ATM network
A virtual channel is established between two end users of the network
To set up a virtual path, there must first be a virtual channel to the destination node
Data over one virtual channel is always transferred at a constant bit rate
When traffic parameters are negotiated, agreement must be reached on:
Average transmission rate
Maximum (peak) transmission rate
Over how many bits of the ATM cell header is the header error control field calculated?
32
16
24
40
In which phase is the receiver of an ATM cell as long as header errors are being detected (and corrected)?
Correction phase
Detection phase
If an error occurs in how many bits will it be corrected at the receiver?
One
Two
Three
Four
Congestion in a data network occurs when the number of control signals to be transferred approaches the __ number that can be transferred:
Minimum
Maximum
Average
None of the listed answers
Congestion in a network occurs when the number of data packets being transferred approaches the __ number of packets that can be transferred:
Minimum
Maximum
Average
None of the above
When congestion occurs in a data network, which parameters decrease?
Network performance
Throughput (transfer speed)
Network reliability
Packet delay time
Traffic intensity
The size of the waiting queue at each node is:
Constant
Dynamically changing depending on traffic in the node
Finite
Infinite
Always greater than 8
In a node, packets usually arrive with a rate that is ___ the rate at which packets are forwarded/sent from the node:
Higher than
Lower than
Equal to
Lower than or equal to
In which networks is the backpressure technique used for congestion control?
X.25
ATM
ISDN
Frame Relay
In the choke packet technique, in which node(s) is the choke packet generated?
In the source node
In the destination node
In the node where congestion has occurred
In all nodes
Which of the following is an example of a choke packet?
ICMP Source Quench
IGMP Source Quench
ICMP Destination Quench
IMCP Source Quench
Which are advanced techniques for congestion control?
Explicit congestion signaling
Implicit congestion signaling
Direct congestion signaling
Indirect congestion signaling
Which are techniques for implicit congestion signaling?
Backward
Forward
Binary
Credit-based
Rate-based
In rate-based explicit congestion signaling, what is defined?
The maximum data rate at which the source may send packets
The minimum data rate at which the source may send packets
The maximum data rate at which the receiver may receive packets
The minimum data rate at which the receiver may receive packets
How many QoS (quality of service) priority levels are defined, as an aspect to consider in congestion control?
(a)
With explicit congestion-avoidance techniques in frame-based networks, who is notified?
Sender
Receiver
End systems
All nodes in the network
Do the basic functions of frame relay natively support explicit congestion signaling?
Yes
No
Which statements are true for LANs?
LANs have lower capacity than WANs
LANs cover a larger geographic area than MANs
LANs use bandwidth up to 100 Mbps
LANs have higher capacity than WANs
LANs use bandwidth from 100 Mbps up to 1 Gbps
Which characteristics must every backend network satisfy?
Bandwidth up to 10 Mbps
Centralized access to the transmission medium
Unlimited number of devices in the network
High-speed interface
Bandwidth of 100 Mbps
Which OSI layers are network-independent (do not depend on the specific network)?
Physical layer
LLC (Logical Link Control) sublayer
Network layer
Session layer
Application layer
Which are accepted LAN topologies?
Ring
Bus
Extended star
Star
Tree
MAC protocol ensures ordered and efficient use of the medium. Control can be implemented in two ways; which is true?
In distributed control, the admin configures each device with the order in which it will send packets
In centralized control, there is a controller that decides which device may access the network
Performance with centralized control is always better than with distributed control
In distributed control, each device maintains simple logic for accessing the network
Asynchronous medium access schemes are:
Round robin
Reservation technique
Contention
FCFS
Priority scheme
Which are fields in every MAC frame?
Destination MAC address
Source MAC address
MAC control
Sender IP address
FCS
How many types of operations are implemented in the LLC protocol?
2
3
4
5
6
Which statements are true about LLC (Logical Link Control)?
Operation type 2 uses the synchronous balanced mode from HDLC
All operation types use numbered PDUs
DSAP and SSAP fields are 8 bits and define destination and source LLC user
DSAP and SSAP fields are 7 bits and define destination and source LLC user
Operation type 1 uses the synchronous balanced mode from HDLC
By transmission technique, wireless LANs are divided into:
Infrared
Narrowband microwave
Satellite
Ad-hoc
Wideband (spread-spectrum) microwave
100Base-T Ethernet LAN has a transmission rate of __ Mbps:
1
10
100
1000
10Base2 Ethernet LAN has a rate of __ Mbps:
1
2
The “T” in 10Base-T and 100Base-T stands for:
Data rate
Type of cable (twisted pair)
Type of signal
Each station in a(n) ___ network is identified by a unique 6-byte physical address.
Ethernet
Token Ring
FDDI
All of the above
Which companies were responsible for creating and implementing the first Ethernet LAN standard?
Digital (DEC)
Microsoft
Intel
Xerox
Cisco
In which of the following cases is a straight-through cable used?
Router – switch
PC – hub
Router – router
Router – PC
Switch – PC
What is the most commonly used LAN technology?
FDDI
Coaxial
Ethernet
Token Ring
Which Ethernet characteristics contributed to its massive use?
Easy to maintain
Collision-free technology
Which statements about CSMA/CD are true?
It is a media access method used in LANs
When a device wants to transmit, it checks if the medium is free
Only one device can successfully transmit at a time
It is used in WANs
The device sends without checking the medium, because all devices have equal access
What type of cable is used between a terminal and a console port?
Cross-over
Straight-through
Rollover
Patch
Which switching method forwards a frame as soon as the destination MAC address is known?
Fragment-free
Cut-through
Store-and-forward
Latency forwarding
What is the disadvantage of cut-through switching?
No error checking
Reduced error checking
Reduced number of collision domains
Reduced bandwidth
Increased latency
What can help with excessive collisions in a LAN?
Reduce the number of broadcast domains
Add managed switches
Add additional transceivers
Add more hubs
Reduce the size of collision domains
Which are IEEE-defined sublayers of the OSI Data Link layer?
Logical Link Control
Logical Link Communication
Media Access Control
Logical Layer Control
Media Access Communication
What is the length of a MAC address?
24 bits
48 bits
8 bits
8 bytes
24 bytes
What happens in an Ethernet network when a collision occurs?
The backoff algorithm is invoked and transmission stops
Devices involved in the collision get a random priority period for retransmission
Devices involved in the collision have no transmission priority afterwards
Devices with data to send return to listen-before-transmit mode
Transmission restarts with “successful” delivery of all data
Where is the MAC address stored?
DHCP server database
Configured by the administrator
Burned into ROM on the NIC
In the OS network configuration
Built into the CPU chip
Which are included in the address field of a frame?
Final (destination) IP address
Final subnet mask
Source MAC address
Destination MAC address
Which network devices split a network into separate collision domains?
Bridge
Switch
AUI
Which term refers to the way a network is arranged, physically or logically?
line configuration
topology
transmission method
modulation method
If the line is divided so one device controls traffic and others must transmit through it, the connection is:
peer-to-peer
point-to-point
primary-secondary
master-slave
