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CSE 6250 CP > 7 - Rate Limiting and Traffic Shaping > Flashcards

7 - Rate Limiting and Traffic Shaping Flashcards

1
Q

Data Traffic Classifications

A

Bursty, periodic, and regular

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2
Q

Audio Traffic Classifications

A

Continuous, and Periodic

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3
Q

Video Traffic Classifications

A

Continuous, bursty, and periodic

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4
Q

Two kinds of traffic

A

Constant Bit Rate Source (CBR) Variable Bit Rate Source (VBR)

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5
Q

CBR

A

Constant Bit Rate Source - Examples are Audio - Shaped according to a peak rate

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6
Q

VBR

A

Variable Bit Rate source - Examples are Video and Data - Shaped according to average and peak rate where average rate is small fraction of peak rate

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7
Q
A

VBR

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8
Q
A

CBR

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9
Q

Leaky Bucket

A

Each flow has own bucket

Beta = size of bucket

Rho = drain rate of bucket (“regulator”)

Accomodates different burst rates by ensuing the packets are always delivered at a constant rate Rho.

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10
Q

(r, t) Traffic Shaping

A

Traffic divided into T-bit frames.

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

If a sender wants to send more than r bits, it needs to wait until next T-bit frame

Known as (r,t) smooth traffic shaping

Limited to fixed rate flows

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11
Q

(r, t) Traffic Shaping compared to Leaky Bucket

A

(r, t) Traffic shaping is slightly relaxed compared to Leaky Bucket. In (r,t) rather than sending a packet every time unit like Leaky BUcket, a sender can send a certain number of bits every time unit.

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12
Q

What happens if a flow exceeds a rate?

A

Excess packets in flow are given lower priority or preferentially dropped

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13
Q

Where are packet priorities set?

A

Sender or Network

Sender - App may mark own packets as it knows which are most important

Network - Marks some packets lower priority called “policing”

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14
Q

Token Bucket

A

For shaping bursty traffic but still ensure flow does not exceed average rate

Rho - Rate tokens arrive in bucket

Beta - Capacity of bucket

Traffic can arrive at rates lambda avg or lambda peak

Need to wait until there are b tokens in the bucket before sending

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15
Q

Token Bucket vs Leaky Bucket

A

Leaky bucket:
Parameters: rate
1. Smooth 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.

Token bucket:
Params: rate, burstiness.
1. Token bucket smooths traffic too but permits burstiness - which is equivalent to the number of tokens accumulated in the bucket.
2. Discards tokens when bucket is full, but never discards packets (infinite queue).
3. Application: Network traffic shaping or rate limiting.

  1. Difficult to police traffic flow. Need to limit how long a sender can monopolize network
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16
Q

Composite Shaper

A

Used to apply policing to token bucket

Combines token and leaky bucket

Confirming that flow data rate does not exceed rate allowed by smoothed leaky bucket

More complex, requies 2 timers and 1 counter for each bucket

17
Q

Token Buffer Shaper

Beta = 100KB

Rho = 10 packets/sec

T interval =1 sec

Packet Size = 1KB

(Flow <= B + T * r data in any interval)

Max Rate in Kb?

A

B + (T * r)

Max Rate = 100KB + 10KB/s(1 sec) = 100KB + 10KB = 110KB = 880 kbs

18
Q

Power Boost

A

First Deployed June 2006 Comcast

Allows subscriber to send at higher rate for brief period of time

Targets spare capacity for those that don’t put sustained load on network

Can be capped or uncapped

19
Q

Calculating Powerboost Rates

R(sustained) = 10Mbps

r(boost) 15Mbps

B = 1 Mbyte

How long can sender send at r (solve for d)?

A

d = B /(r - Rsus)

d = 1Mbyte/(15Mbps-10Mbs) =8Mbits/5Mbs=1.6 seconds

20
Q

Power Boost and Latency

A

Users may experience high latency and loss due to power boost

Reason is access link may not be able to support higher rate

Buffers will fill up and introduce delays because difference in rate between boost and access link rate

21
Q

How to solve Power Boost Latency

A

Send should limit sending rate to that of the access link (sustained rate)

22
Q

Buffer Bloat

A

Example is latency effect of power boost

Issue is buffer is filled up by temporary boost rate.

This increases latency due to waiting for buffer to drain at slower rate

23
Q

Buffer Bloat Solutions

A
  1. Smaller Buffers
  2. Shaping Traffic in router to match uplink rate
24
Q

Two Types of Network Measurment

A

Passive Measurement: Measuring packets and flows already on network

Active Measurment: Inject additional traffic and measure characteristics (ping or trace route)

25
Q

Ping

A

Used to measure network delay to a server

26
Q

Trace Route

A

Used to measure network level or IP level path between two hosts

27
Q

Why measure the network?

A

Billing (95 Percentile rate)

Security (compromised hosts, botnets, DoS)

28
Q

How to measure passively?

A

SNMP(Simple Network Management Protocol) provides packet and byte counters

  • Many network devices provide a (MIB) Management Information Base can be polled.
  • Poll interface on packets sent over intervals.

Packet Monitoring

Flow Monitoring

29
Q

SNMP Pros and cons

A

Simple Network Management Protocol

+ Ubiquitous on most network devices

  • Course cannot expess complex queries on data. Only polling byte and packet counts, can’t ask questions such as how much traffic per host or flow
30
Q

Packet Monitoring

A

Full packet contents or headers

tcpdump, ethereal, wireshark

Also hardware can perform packet monitoring in routers

Advantage: Lots of detail

Disadvantage: Lots of overhead, may need special hardware

31
Q
  • Flow Monitoring
A

Monitors statistics per flow

A flow consists of packets that share commone src dest ip/port/protocol type/tos byte/interface

Groups packets by above features.

Also can group by next-hop IP or src/dest AS & prefix

+ less overhead

  • more course, no packet payload level detail
  • must appear close together in time

Can sample randomly

32
Q

Timing Information can be provided by packet or flow monitoring?

A

Packet only

33
Q

Packet Header information can be proviced by packet or flow monitoring?

A

Packet

34
Q

Number of bytes per flow can be provided by packet or flow monitoring?

A

Both

CSE 6250 CP (1 decks)

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