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Networking > QoS and Congestion > Flashcards

QoS and Congestion Flashcards

1
Q

Monitoring the system for QoS

A

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

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2
Q

QoS Skip

A

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

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3
Q

A flow

A

Stream of packets from source to destination

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4
Q

Why do we need flow

A

Due to bandwidth, jitter and delay

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5
Q

Retransmissions

A

used to restore lost data partially

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6
Q

When an application can enhance network service

A

Network requirements are less demanding than application requirements

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7
Q

Buffering packets at receiver

A

Reduce jitter

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8
Q

Jitter

A

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

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9
Q

Why can video sustain lost frames

A

they go unnoticed if they aren’t in abundance

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10
Q

Networks support different categories of QoS

A

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

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11
Q

Guarantee high QoS

A

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

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12
Q

Issues to address to help QoS

A

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.

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13
Q

Load shedding

A

removes excess load

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14
Q

Link Bandwidth

A

Network must apportion bandwidth between different flows.

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15
Q

Queue Space

A

Defines which packets should be dropped

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16
Q

When too much traffic is offered

A

congestion sets in and performance degrades sharply.

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17
Q

Goodput

A

Rate at which useful packets enter the network

18
Q

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

A

In a datagram network.

19
Q

If all routers had infinite memory

A

Congestion would get worse.

20
Q

Bufferbloat

A

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

21
Q

How to solve bufferbloat

A

Load shedding, or providing additional capacity

22
Q

Congestion Control

A

Behavior of all the hosts and routers.

23
Q

Traffic Management

A

Making sure the network is able to carry the offered traffic

24
Q

Flow Control

A

Relates to traffic between specific sender and receiver.

25
Q

Approaches for building a good network

A

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

26
Q

Traffic Aware routing

A

Enable mobile listeners to route packets around hotspots

27
Q

What to do if you cant increase capacity of a network

A

Lighten the load

28
Q

Virtual Circuit Network

A

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

29
Q

Admission control

A

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

30
Q

Strategies to drop packets that networks are unable to deliver

A

Traffic Shaping and Traffic Policing

31
Q

Traffic Shaping

A

Limits transmissions from a particular sender

32
Q

Traffic Policing

A

Dropping traffic from a particular sender if it exceeds some rate

33
Q

Divert traffic from hotspots

A

By factoring in load when calculating routes

34
Q

How to factor in load when calculating routes

A

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

35
Q

Traffic Aware Routing Downfall

A

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

36
Q

Traffic Aware routing unsecurity

A

If routing through unsafe parts of a network

37
Q

Successful solutions for traffic aware routing

A

Gallaghers routing method and Multipath routing

38
Q

Multipath Routing

A

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

39
Q

Gallagher’s routing method

A

Move traffic between routes slow enough to allow it to converge

40
Q

Difficulties of traffic aware routing

A

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

Networking (7 decks)

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