Rate Limiting and Traffic Shaping

Question 1

Classification of traffic sources: Data

Answer 1

1. Bursty
2. Periodic
3. Regular

Question 2

Classification of traffic sources: Audio

Answer 2

1. Continuous

2. Periodic

Question 3

Classification of traffic sources: Video

Answer 3

1. Continuous
2. Bursty (due to how video is compressed)
3. Periodic

Question 4

Constant Bit Rate: example

Answer 4

Audio

Question 5

Variable Bit Rate: example

Answer 5

Video and Data

Question 6

Leaky Bucket

Answer 6

Traffic arrives in a bucket of size beta and drains from bucket at a rate rho

1. Smooths out traffic by passing packets only when there is a token. Does not permit burstiness.
2. Discards packets for which no tokens are available (no concept of queue)
3. Application: Traffic shaping or traffic policing.

Question 7

(r, T) Traffic Shaping

Answer 7

1. Traffic Divided in to T-bit frames

2. Flow can inject >= r bits into T-bit frams

Question 8

What happens when flow exceed rate in (r, T) Traffic Shaping?

Answer 8

The excess packets are assigned a lower priority

Question 9

Policing

Answer 9

When the network (as opposed to the sender) marks packets for lower priority.

**this refers to (r, T) traffic shaping

Question 10

Type of bucket: shaping bursty traffic

Answer 10

Token Bucket

Question 11

Token bucket: Rate

Answer 11

rate < B + (rho*T)

T = time interval
B = bucket size
rho = rate at which token accumulate

Question 12

Token bucket: characteristics

Answer 12

1. Permits burstiness, but bounds it

2. No discard or priority

Question 13

Leaky bucket: characteristics

Answer 13

1. smooths bursty traffic

2. has priority policies

Question 14

Power Boost: Definition

Answer 14

1. Allows users to send at higher rate for a brief period of time

Question 15

There are 2 types of Power Boost

Answer 15

1. Capped

2. Uncapped

Question 16

Uncapped Power Boost (explanation)

Answer 16

The original max rate is rho.

The higher rate is rho(c).

The area of the boosted segment is beta. This is the size of the token bucket.

Question 17

Buffer Bloat: explained

Answer 17

1. Even if a sender can burst at high speed, the buffer can only be drained at a rate Rsus.

Question 18

Buffer bloat delay calculation

Answer 18

delay = data in buffer / Rsus

Question 19

Buffer Bloat: solutions

Answer 19

1. Smaller buffers

2. Traffic shaping (of your home router)

Question 20

Passive measurement: definition

Answer 20

Collect traffic that is already being sent on the network

a. packets
b. flow statistics
c. application logs

Question 21

Active measurement: definition

Answer 21

inject extra traffic into the network

a. ping
b. traceroute

Question 22

Passive Measurement: SNMP

Answer 22

Simple Network Management Protocol

1. Poll the Management information base (MIB) for particular information

Question 23

Passive Measurement: packet monitoring

Answer 23

Wireshark (basically)

Question 24

Passive Measurement: flow monitoring

Answer 24

1. A flow is basically all packets/traffic from one particular source
2. Less precise than packet monitoring (since you aren’t capturing all packets)