QoS and Congestion

Question 1

Monitoring the system for QoS

Answer 1

Determine where and when congestion occurs. Pass info to where action can be taken. Adjust system operation to correct problem.

Question 2

QoS Skip

Answer 2

use Label Switching or MPLS for good QoS, Integrated services, or Differentiated services.

Question 3

A flow

Answer 3

Stream of packets from source to destination

Question 4

Why do we need flow

Answer 4

Due to bandwidth, jitter and delay

Question 5

Retransmissions

Answer 5

used to restore lost data partially

Question 6

When an application can enhance network service

Answer 6

Network requirements are less demanding than application requirements

Question 7

Buffering packets at receiver

Answer 7

Reduce jitter

Question 8

Jitter

Answer 8

Variations in delay or packet arrival times. Easily noticed on audio or video.

Question 9

Why can video sustain lost frames

Answer 9

they go unnoticed if they aren’t in abundance

Question 10

Networks support different categories of QoS

Answer 10

Constant bitrate, Realtime variable bitrate, Non realtime variable bitrate, Available bitrate.

Question 11

Guarantee high QoS

Answer 11

design a network with enough capacity for traffic. Overprovisioning and expensive. Low latency and no loss. Best performance.

A network with less requirements can still match this using QoS techniques

Question 12

Issues to address to help QoS

Answer 12

What application requires from a network. How to control traffic entering network. How to make resource reservations at router. If extra traffic can be accommodated safely on network.

Question 13

Load shedding

Answer 13

removes excess load

Question 14

Link Bandwidth

Answer 14

Network must apportion bandwidth between different flows.

Question 15

Queue Space

Answer 15

Defines which packets should be dropped

Question 16

When too much traffic is offered

Answer 16

congestion sets in and performance degrades sharply.

Question 17

Goodput

Answer 17

Rate at which useful packets enter the network

Question 18

It is impossible to avoid congestion completely in a ______ network.

Answer 18

In a datagram network.

Question 19

If all routers had infinite memory

Answer 19

Congestion would get worse.

Question 20

Bufferbloat

Answer 20

Network devices have more memory than needed. Senders need timely information about congestion, as packets are stored in router buffer instead of being dropped.

Question 21

How to solve bufferbloat

Answer 21

Load shedding, or providing additional capacity

Question 22

Congestion Control

Answer 22

Behavior of all the hosts and routers.

Question 23

Traffic Management

Answer 23

Making sure the network is able to carry the offered traffic

Question 24

Flow Control

Answer 24

Relates to traffic between specific sender and receiver.

Question 25

Approaches for building a good network

Answer 25

Build network provisioned for traffic it needs to carry. Resources can be added dynamically when there is congestion. Links and routers must be upgraded. Routes can be modified for changing traffic patterns. Divert traffic from heavily used routes

Question 26

Traffic Aware routing

Answer 26

Enable mobile listeners to route packets around hotspots

Question 27

What to do if you cant increase capacity of a network

Answer 27

Lighten the load

Question 28

Virtual Circuit Network

Answer 28

If a new connection congests the network, it could be rejected. Illustration of admission control.

Question 29

Admission control

Answer 29

Forbids senders from sending traffic if the networks capacity cannot accommodate it

Question 30

Strategies to drop packets that networks are unable to deliver

Answer 30

Traffic Shaping and Traffic Policing

Question 31

Traffic Shaping

Answer 31

Limits transmissions from a particular sender

Question 32

Traffic Policing

Answer 32

Dropping traffic from a particular sender if it exceeds some rate

Question 33

Divert traffic from hotspots

Answer 33

By factoring in load when calculating routes

Question 34

How to factor in load when calculating routes

Answer 34

Setting link weight to be a function of the fixed link bandwidth, propagation delay, observed load or average queueing delay

Question 35

Traffic Aware Routing Downfall

Answer 35

If routing algorithm sends all data through a particular network segment, can increase traffic leading to congestion.

Question 36

Traffic Aware routing unsecurity

Answer 36

If routing through unsafe parts of a network

Question 37

Successful solutions for traffic aware routing

Answer 37

Gallaghers routing method and Multipath routing

Question 38

Multipath Routing

Answer 38

There may be multiple ways of getting from A to B by taking another path

Question 39

Gallagher’s routing method

Answer 39

Move traffic between routes slow enough to allow it to converge

Question 40

Difficulties of traffic aware routing

Answer 40

routing protocols do not change according to load. Instead traffic engineering is used. Now, some software defined networking automates some of these tasks.