Deck 20: Congestion Control

Question 1

Congestion control is concerned with efficient use of a network at high load.

Answer 1

True

Question 2

_________ explicit congestion signaling approaches notify the user that congestion avoidance procedures should be initiated where applicable for traffic in the same direction as the received notification.

A)Datagram
B)Dynamic
C)Forward
D)All of the above

Answer 2

C

Question 3

Congestion control on the basis of implicit signaling requires action on the part of network nodes.

Answer 3

False

Question 4

For ________ congestion avoidance,the network alerts end systems to growing congestion within the network and the end systems take steps to reduce the offered load to the network.

A)backpressure
B)explicit
C)implicit
D)dynamic

Question 5

One of the things that may happen when network congestion occurs is packets are discarded.

Question 6

In a rate based scheme any node along the path of the connection can reduce the data rate limit in a control message to the source.

Question 7

If the rate at which packets arrive and queue up exceeds the rate at which packets can be transmitted,the queue size grows without bound and the delay experienced by a packet goes to infinity.

Question 8

The objective of __________ is to maintain the number of packets within the network below the level at which performance falls off dramatically.

A)fast restraint
B)traffic management
C)window management
D)congestion control

Question 9

______ is a congestion control technique.

A)Choke packet
B)Implicit congestion signaling
C)Backpressure
D)All of the above

Question 10

Even if all sources can detect congestion and reduce flow on the basis of congestion,network congestion still will not be relieved.

Question 11

Token bucket is used in the Bluetooth specification.

Question 12

Congestion is only a critical problem for certain types of switched data networks.

Question 13

Traffic policing is concerned with traffic leaving the switch.

Question 14

An example of a choke packet is the ICMP Source Quench packet.

Question 15

The size of TCP's send window can have a critical effect on whether TCP can be used efficiently without causing congestion.

Question 16

When a TCP entity retransmits a segment using fast retransmit it assumes that a segment was lost,even though it has not yet timed out on that segment.

Question 17

A reservation scheme is an integral part of ATM networks.

Question 18

With the ________ approach a bit is set in a data packet as it is forwarded by the congested node.

A)forward
B)binary
C)credit based
D)rate based

Question 19

Backpressure is a technique for congestion control.

Question 20

Explicit congestion signaling approaches work forward but not backward.

Question 21

The purpose of the ________ mechanism is to gradually expand the window until acknowledgments are received.

A)slow start
B)window management
C)backpressure
D)none of the above

Question 22

A common technique for predicting the next value on the basis of a time series of past values,and the one specified in RFC 793,is _________.

A)Jacobson's algorithm
B)token bucket
C)exponential averaging
D)implicit congestion signaling

Question 23

Typically,_______ congestion control techniques operate over connection-oriented networks and control the flow of packets over individual connections.

Question 24

________ is a measure used in the implementation of TCP congestion control measures.

A)Fast recovery
B)Slow start
C)Exponential RTO backoff
D)All of the above

Question 25

A token bucket traffic specification consists of two parameters: a token replenishment rate and a _________ .

Question 26

A _______ is a control packet generated at a congested node and transmitted back to a source node to restrict traffic flow.

Question 27

________ discriminates between incoming packets that conform to QoS agreement and those that don't.

Question 28

Defined in RFC 4340,__________ is an unreliable connection-oriented protocol that can include mechanisms for detecting congestion by determining round-trip time and packet drop rates.

A)TCP
B)RTT
C)DCCP
D)RTO

Question 29

The ________ scheme provides the input parameters to a policing function.

Question 30

_________ refers to flows that will back off appropriately in the face of congestion.

A)TCP friendly
B)Fast recovery
C)Congestion collapse
D)Backpressure

Question 31

__________ schemes are based on providing an explicit data rate limit to the source over a logical connection.

A)Backward
B)Rate based
C)Forward
D)Binary

Question 32

_________ occurs when the number of packets being transmitted through a network begins to approach the packet-handling capacity of the network.

Question 33

_________ schemes are common for end-to-end flow control,in which a destination system uses credit to prevent the source from overflowing the destination buffers.

A)Rate based
B)Backward
C)Binary
D)Credit based

Question 34

A ________ fills at a constant rate up to the capacity of the bucket and empties at a rate dictated by the input data stream while the bucket is not empty.

A)leaky bucket
B)choke packet
C)slow start
D)token bucket

Question 35

One aspect of a reservation scheme is _______,in which a node in the network monitors the traffic flow and compares it to the traffic contract.

A)traffic policing
B)window management
C)congestion control
D)RTT variance estimation

Question 36

________ is an effective congestion control technique in connectionless,or datagram,configurations,such as datagram packet-switching networks and IP-based internets.

Question 37

Fairness,QoS,and reservations are all issues related to congestion control that fall into the category of __________ .

Question 38

The ________ specifies the amount by which the data rate can exceed the token rate for short periods of time.

A)bucket size
B)choke packet
C)reservation
D)exponential average

Question 39

Explicit congestion signaling approaches can be divided into three general categories: Credit based,rate based,and ________ .

Question 40

________ is aimed at smoothing out traffic flow by reducing packet clumping that leads to fluctuations in buffer occupancy.

Question 41

__________ proposed two procedures,called fast retransmit and fast recovery,that under some circumstances improve on the performance provided by RTO.

Question 42

The TCP congestion control measure techniques fall into two categories: retransmission timer management and ________ management.

Question 43

A _________ empties at a constant rate while the bucket is not empty and fills at a rate dictated by the input stream up to the capacity of the bucket.

Question 44

An example of _________ signaling is the explicit congestion notification capability provided in IP and TCP and defined in RFC 3168.

Question 45

________ algorithm addresses RTT variance estimation.