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Networking > Rate limiting and traffic shaping > Flashcards

Rate limiting and traffic shaping Flashcards

1
Q

data classification (traffic)

A

Bursty, Periodic, regular

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2
Q

audio classification (traffic

A

continuous, periodic

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3
Q

video classification (traffic)

A

continuous, periodic, bursty

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4
Q

Two rate classes

A

CBR and VBR

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5
Q

CBR

A

Constant Bit Rate source (audio)

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6
Q

VBR

A

Variable Bit Rate source (video, audio)

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7
Q

How is CBR shaped

A

Peak Rate

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8
Q

How is VBR shaped

A

Average and peak rate

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9
Q

leaky bucket shaper

A

you have a buffer Beta that can be thought of as having a leaky whole. Rho is the drain rate that acts as a regulator.

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10
Q

(R, T) packet shaping

A

Traffic is divided into T-bit frames

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

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11
Q

What to do when a flow exceeds rate? (leaky bucket)

A

Packets are given a lower priority or in the worse case dropped

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12
Q

What is used to shape bursty traffic?

A

Token Bucket

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13
Q

What is a token bucket

A

we have a rate rho at which tokens are placed in the bucket. Lambda(peak) = peak rate. Lambda(avg) = average rate.

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14
Q

What happens when the token bucket is full?

A

If we are sending a packet of size b: if bucket is full, packet is sent, b tokens removed.

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15
Q

What happens when the token bucket is empty

A

Empty pack must wait until b tokens arrive.

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16
Q

What happens when the token bucket is partially full?

A

If number of tokens exceeds b send otherwise wait

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17
Q

Token Bucket main points

A

Permits burst but bounds it. If any T, rate < Beta + T * rho, longterm < rho, no discard or priority, difficult to policy

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18
Q

Leaky Bucket main points

A

Forces to be smooth, Priority policy

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19
Q

How does Policing with token buckets work?

A

Link a token bucket with a leaky bucket. When the traffic leaves the token bucket it is added to a leaky bucket.

20
Q

Power Boost

A

Allows for subscribers to send at a higher rate for some period of time. Spare capacity for users who do not put sustained load on the network.

21
Q

Calculating Powerboast Rates

A

Sending rage r > Rsustained. d is how long the sender can exceed the sustained rate. We can then computer the area Beta by taking the product of d and the difference of r and Rsustained.

22
Q

What did project Bismark discover

A

Powerboost may introduce long delays since the rapid increase in traffic might be a faster rate then the network can handle causing buffers to fill up.

23
Q

How could the issue with Powerboost be corrected?

A

They could run a packet shaper to avoid latency issues

24
Q

Buffer Bloat

A

Buffers can only drain at Rsustained. Delay = (Data in buffer / Rsustained)

25
Q

How can a traffic shaper help correct Buffer Bloat

A

Make sure that the traffic entering the cable modem doesn’t exceed the buffer drain rate (uplink to isp)

26
Q

Two types of network measurement

A

Passive and Active

27
Q

Passive Measurement

A

Collection of packets flow stats that are already on the network

28
Q

Active Measurement

A

inject additional traffic to measure various charateristics

29
Q

Why measure network traffic

A

Billing, Security

30
Q

CIR

A

Committed Information Rate

31
Q

What are somethings security monitoring checks for

A

Compromised Host, Botnets, Denial of Service (dos)

32
Q

SNMP

A

Simple Network Management Protocol

33
Q

MIB

A

Management Information Base

34
Q

What is MIB used for

A

Periodically poll the interface to determine the number of bytes or packets being sent to determine the rate

35
Q

What is the advantage of SNMP?

A

Ubiquitous supported on majority of devices Number of tools available to analysis the data

36
Q

Down side to SNMP

A

Hard to query. Coarse since just getting the count

37
Q

List 3 passive monitoring types

A

Packet, flow, snmp

38
Q

Packet Monitoring

A

Can see full packet content (for packet header)

39
Q

What are some Packet Monitoring tools

A

tcpdump, ethereal, wireshark, hardware cards

40
Q

Flow monitoring

A

monitors record statistics per flow

41
Q

What is a flow in flow monitoring

A

source and destination IP, Source and Destination Part, Protocol type, tos byte, interface, next hop id, source destination AS and prefix, Close together in time

42
Q

Pro Cons Flow vs Packet monitoring

A

Pro: Less Overhead, Con: more coarse, no packet/payloads

43
Q

Technique to reduce flow level monitoring overhead?

A

Sampling: builds flow stats y only taking samples of the packets

44
Q

Timing information: Packet, Flow or Both

A

Packet

45
Q

Packet Headers: Packet, Flow or Both

A

Packet

46
Q

Number of bytes in each flow: Packet, Flow or Both

A

Both

Networking (8 decks)

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