Rate Limiting and Traffic Shaping Flashcards Preview

CS6250 Test 2 - PHIL > Rate Limiting and Traffic Shaping > Flashcards

Flashcards in Rate Limiting and Traffic Shaping Deck (28):
1

Traffic Shaping Approaches (3)

Leaky Bucket

(r, T) Traffic Shaping

Token Bucket

2

Motivation for traffic shaping

-resource control

-ensure flows don't exceed drain rate

3

Source Classifications and attributes for each one

Data: regular, bursty, periodic

Audio: continuous, periodic

Video: continuous, bursty, periodic

4

Sourse Classes

CBR: constant bit rate

VBR: variable bit rate

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CBR

constant bit rate: arrives at regular intervals and at regular lengths (audio)

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VBR

variable bit rate: like video and data. Arrives at variables intervals and lengths

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What is constant bit rate shaped by?

peak rate

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What is variable but rate shaped by?

average and peak rate

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leaky bucket shaping attributes

beta: size of bucket

row: drain rate of bucket (maximum smooth rate)

Size of bucket controls the burst rate. As long as size of the burst does not exceed size of bucket, sender can send at faster rate.

-smooths bursty traffic

-priority policies for flows that exceed smoothing rate

10

(r, T) traffic shaping attributes

-traffic divided into T-bit frames

-flow can inject <= r bits in any T-bit frame

-typically used for fixed flows

11

what is "(r, T) smooth"?

optimal property achieved when (r, T) traffic shaping is implemented

12

what is policing?

it is process by which packets are given priority assignments by the sender or within the network

13

token bucket attributes

-row = rate at which tokens are placed in the bucket

-traffic is sent by the regulator as long as there are tokens in the bucket

-permits burstiness, but bounds it

- long term rate < row

-no discard or priority/policing

14

problem with standard token bucket

lack of policing means that it can monopolize network resources by interfering with other high priority traffic

15

How to police with a token bucket?

You must use a composite shaper (leaky bucket + token bucket)

16

Composite shaper attributes

-combination of leaky bucket and token bucket

-more complex because you need 1 counter and 1 timer for each bucket

17

token bucket shaper max rate calculation

max = beta + (timeInterval * row)

18

what is power boost?

Technology which allows a subscriber to temporarily send @ higher rate than the sustained rate

19

2 types of power boost are:

capped and uncapped

-capped uses a second token bucket w/ additional 'row'; value

-uncapped: power boost window is the bucket size

20

power boost variables

- sending rate: r

- sustained rate: Rsus

-power boost bucket size: beta

-time: d

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power boost bucket formula

beta = d * (r - Rsus)

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power boost time formula

d = beta / (r- Rsus)

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potential problem and solution to power boost

rate at which data sent during the PB may exceed the access link's ability to service the packets. So buffer may fill up.

The solution to this is to place a traffic shaper in front of the power boost so that the rate never exceeds Rsus

24

what is buffer bloat?

In the presence of a network buffer, delay experienced by sender. This is because if buffer is large, sender won't see dropped packets until the buffer is full, causing delay.

25

solutions to buffer bloat

-smaller buffers (hard to do since network infrastructure already deployed)

-shaping: ensure sending rate never exceeds the drain rate of the access link

26

types of network measurement

passive and active

passive: collection of packets, flow states already on network

active: inject additional traffic to measure characteristics (ping, traceroute)

27

why measure

-billing (95th percentile billing)

-security (compromised hosts, botnets, DOS)

28

packet delay calculation

data in buffer / Rsus