Download Network Design and Analysis

© Graduate University , Chinese academy of Sciences.
Network Design and
Performance Analysis
Wang Wenjie
[email protected]
Network Design and Analysis-----Wang Wenjie
Introduction: 1
© Graduate University , Chinese academy of Sciences.
What the Course is about
• 随着计算机通信、电信网络等系统的发展，统计性能评价方
法变得越来越重要。统计性能评价是关于复杂的网络或软件
等系统的行为预测的问题，它是使用数学方法以及计算机等
工具进行分析的方法。
• This course is about computer communications
network planning , design and analysis
Network Design and Analysis-----Wang Wenjie
Introduction: 2
© Graduate University , Chinese academy of Sciences.
Learning Objectives(1)
• Upon successful completion of this course, you will
be able to …
– Apply analytical models to evaluate the relative
performance of single and multiple queue systems used to
model networks and protocols
– Describe traffic models used for packet switched traffic and
discuss the concept of self-similarity and its applicability to
network modeling
– Design simulation experiments, develop traffic models,
develop network models, and analyze results for evaluating
the performance of queues, local area networks,
internetworks, and protocols
Network Design and Analysis-----Wang Wenjie
Introduction: 3
© Graduate University , Chinese academy of Sciences.
Learning Objectives(2)
• Upon successful completion of this course, you will
be able to (continued) …
– Apply modeling and network design techniques to design
data networks based on performance objectives and design
constraints
– Explain the use of network management tools and network
monitors to determine network performance and
operational problems
Network Design and Analysis-----Wang Wenjie
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Course Agenda
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绪论
随机变量和随机过程简介
排队论
自相似过程
Petri网络介绍
多路访问协议
拥塞控制
路由选择
Network Design and Analysis-----Wang Wenjie
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© Graduate University , Chinese academy of Sciences.
Course Information
• Who is the course for?
– Graduate Students
• Grading
– Homework:
• Assignments
• Programming
– Final Exam :
Network Design and Analysis-----Wang Wenjie
Introduction: 6
© Graduate University , Chinese academy of Sciences.
Reading list
• Bertsekas D. & Gallager R., Data Networks – Second
Edition, Prentice-Hall, 1992
（中文：数据网络，人民邮电出版社）
• Stallings W., High-Speed Networks: TCP/IP and ATM
Design Principles, Second edition, Prentice Hall, 2002
（中文：高速网络与互联网，电子工业出版社）
• Thomas G. Robertazzi, Computer Networks and
Systems: Queueing Theory and Performance
Evaluation, 3rd edition, Springer-Verlag, 2000 (ISBN 0387-95037-0).
Network Design and Analysis-----Wang Wenjie
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Introduction
Network Design and Analysis-----Wang Wenjie
Introduction: 8
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Outlines
• Network Models
• Methods for Performance Evaluation
• Quality of Service(QoS)
• Traffic Definitions
Network Design and Analysis-----Wang Wenjie
Introduction: 9
© Graduate University , Chinese academy of Sciences.
Outlines
• Network Models
• Methods for Performance Evaluation
• Quality of Service(QoS)
• Traffic Definitions
Network Design and Analysis-----Wang Wenjie
Introduction: 10
© Graduate University , Chinese academy of Sciences.
Network Models
• What are we modeling?
• Networks (broadly defined) generally fall into
one of three categories
– Resource sharing networks
– Process networks
– Switching networks
Network Design and Analysis-----Wang Wenjie
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Resource sharing networks(1)
• Time-shared computer (Programs : CPU/Disk/IO)
• Statistical multiplexer/concentrator
• Packet-based (Packets : Links)
• Channel-based (Calls : Channels)
• Multiple-Access and random access networks (Packets :
Shared Medium)
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Resource sharing networks(2)
• Performance measures
– Waiting time
– Blocking probability
• Questions
– What is the relationship between the number of
users, the pattern of usage, the amount of
resources, and the performance?
– Are resources utilized fairly (or appropriately) by
the users?
Network Design and Analysis-----Wang Wenjie
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Process networks(1)
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Process networks(2)
Network Design and Analysis-----Wang Wenjie
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Switching networks(1)
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Switching networks(2)
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Outlines
• Network Models
• Methods for Performance
Evaluation
• Quality of Service(QoS)
• Traffic Definitions
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Life Cycle
Performance
Evaluation/Analysis
Network
Design
Network Design and Analysis-----Wang Wenjie
Network
Management
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Design
• A Network Design is a blueprint for building a
network. The Designer has to create the
structure of the network [and] decide how to
allocate resources and spend money
( R. Cahn)
• Tools: Capacity Assignment techniques ,
graph theory, computer projects
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Management
• “(…) our only real option is to use the
network to manage the network. This means
we need a protocol that allows us to read,
and possibly write, various pieces of state
information on different nodes.”
(L. Peterson & B. Davie)
• Tools: SNMP, experiments
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Performance Evaluation
• We will predict the behavior of networks
“using pencil, paper, the poetry of
mathematics and the number-crunching
ability of computers.”
(T. Robertazzi)
• Tools: Queuing theory, traffic models,
simulation
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Need for Performance Evaluation
• The most important concern with a network
system is that it correctly perform its intended
functions
• The second concern is that it has “adequate”
performance at a “reasonable” cost
– “adequate performance” / “reasonable cost” may be
explicitly or implicitly given, and usually determined
largely by the intended functions
– In general, performance and cost are given little
consideration
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© Graduate University , Chinese academy of Sciences.
Methods for Performance Evaluation
There are three main methods used in the design of
performance studies
• Experimental approaches
– measurement and use of a real system
• Analytic approaches
– the use of mathematics, queueing theory, Petri Nets, abstract
models, etc
• Simulation approaches
– design and use of computer simulations and simplified models
to assess performance
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Example: ISP(1)
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Example: ISP(2)
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Example: ISP(3)
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Example: ISP(4)
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Example: ISP(5)
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Example: ISP(6)
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Example: ISP(7)
• Verification
(usually easy to do)
• Is the model properly constructed?
• Analytical model: “Is the math right?”
• Simulation model: “Is the model properly coded?”
• Validation (often hard to do)
• Does the model accurately represent the behavior
of the system of interest?
• Analytical model: “Is the model ‘correct’?”
• Simulation model: “Is this an accurate simulation
for the questions of interest?”
Network Design and Analysis-----Wang Wenjie
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© Graduate University , Chinese academy of Sciences.
Outlines
• Network Models
• Methods for Performance Evaluation
• Quality of Service(QoS)
• Traffic Definitions
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Quality of Service(1)
•
Variety of definitions exist in literature
•
ATM definition- “Quality of Service is the performance observed by an end
user”
•
Internet definition - Still evolving :-)
•
QoS is also usually expressed as the combination of network-imposed
delay, jitter, bandwidth, loss and reliability----------refers to providing a
level of service “acceptable” to network users, e.g.,
– Blocking rate:
Percent of calls blocked that user can accept
– Delay:
Delay time should be less than y milliseconds
– Jitter:
Cell delay variation
Network Design and Analysis-----Wang Wenjie
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© Graduate University , Chinese academy of Sciences.
Quality of Service(2)
Important Performance Parameters
System Blocking
Delay in the messaging
Jitter
Simulation &
Buffer Overflow
Queuing
Packet Loss
Theory
System Reliability
End-to-end delay in media packets
Response Delay
System Recovery Time
Admission Control Algorithm
Game Theory
Resource Scheduling algorithms
System Capacity
Capacity
System Engineering Rules Introduction:
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© Graduate University , Chinese academy of Sciences.
Attributes of QoS(1)
• QoS defines a set of attributes related to the
performance of connection.
– User-related attributes: the attributes that define
how fast the user wants to send data.
– Network-related attributes: the attributes are those
that define characteristics of the network
• QoS parameters need to be mapped between layers
• Application layer QoS Frame rate, size of video
• Network layer QoS bandwidth, Delay
Network Design and Analysis-----Wang Wenjie
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© Graduate University , Chinese academy of Sciences.
Attributes of QoS(2)
• Peceptual Parameter
System QoS
• Picture detail
Pixel resolution
• Picture color accuracy
Maps to color information per pixel
• Video Rate
Maps to frame rate
• Video smoothness
Maps to frame rate jitter
• Audio Quality
Audio Sampling rate and number of bits
• Video/audio synchronisation Video and audio stream synchronised
•
for example lip-sync.
Network Design and Analysis-----Wang Wenjie
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Why needs QoS?(1)
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Why needs QoS?(2)
• The level of service is one of the key
parameters to determine how much resources
should be put in the network
• Equipment utilization:
– This is an associated issue with QoS/GoS , it
is about proper utilization of resources
Network Design and Analysis-----Wang Wenjie
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© Graduate University , Chinese academy of Sciences.
What need for QoS?(3)
• With the notion of QoS for a certain service, we
also need:
– Minimally, have some information on the
amount of demand (which typically refers to
as offered traffic in the context of computer
communication networks)
– Have a way to character the estimate of
traffic
Network Design and Analysis-----Wang Wenjie
Introduction: 39
© Graduate University , Chinese academy of Sciences.
Outlines
• Network Models
• Methods for Performance Evaluation
• Quality of Service(QoS)
• Traffic Definitions
Network Design and Analysis-----Wang Wenjie
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© Graduate University , Chinese academy of Sciences.
Traffic and Traffic Demand
• A network provider has control over design and
management for the network that is under its own
administrative domain; thus, in order to do that , an
important need for each provider would be to
determine traffic demand in its own network
• Traffic in the Internet
• Traffic in the Telephone Network
Network Design and Analysis-----Wang Wenjie
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Traffic in the Internet
• Applications: emails, ftp, web, …
• We do not know ahead of time when and where to
access, use or whether to request a web page ?
--- The Internet data traffic has a statistical property
• Measurement systems need to capture statistics so
that traffic arrival distribution and traffic volume can be
estimated.
--- M/M/1,…
Network Design and Analysis-----Wang Wenjie
Introduction: 42
© Graduate University , Chinese academy of Sciences.
Traffic in the Telephone Network
• The voice circuit is dedicated for one user.
---- Average call arrival rate
---- Average duration of a call
•
offered load or offered traffic is telephony
product of the two factors
• Other notions: Erlang-B loss, carried load or traffic
Network Design and Analysis-----Wang Wenjie
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Example of traffic system（1）
• There are three nodes
• Suppose:
1) Traffic
given in the number of connected is
deterministic
2) Each connection requires one unit of
capacity for a direct link, two units of
capacity through a third node
3) Demand units for a link is direction-less
Network Design and Analysis-----Wang Wenjie
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Example of traffic system（2）
Morning(M) Afternoon(A)
Evening(E)
AB
5
11
8
AC
BC
6
10
13
2
6
7
B
A
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C
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Example Analysis
• If we know how to design the network with
capacity and routing rule in place, and
If it is properly utilized,
then the demand can be met
• Network planning involves determination:
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Network topology
Capacity links and switches
Routing
Network Design and Analysis-----Wang Wenjie
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© Graduate University , Chinese academy of Sciences.
Second problem
• Suppose that we have determined the capacity
and put them in place , and now the traffic
changed slightly, the question is what is the
maximum number of connections that can
accommodated given the capacity?
Network Design and Analysis-----Wang Wenjie
Introduction: 47
© Graduate University , Chinese academy of Sciences.
Third problem
• Consider arrival of two packets streams to a
network node. If we have some kind of flow
control activated for one stream, how is the
system behavior for these traffic streams?
Network Design and Analysis-----Wang Wenjie
Introduction: 48
© Graduate University , Chinese academy of Sciences.
Traffic Definition(1)
QoS Framework
• Static Functions
–
–
–
–
Traffic and QoS specifications (traffic types/parameters)
QoS negotiation and signalling
Admission control
Resource reservation
• Dynamic Functions
– Traffic shaping and policing
– Queuing and scheduling
– Congestion control
Network Design and Analysis-----Wang Wenjie
Introduction: 49
© Graduate University , Chinese academy of Sciences.
Traffic Definition(2)
Traffic Source Types
• CBR (Constant Bit Rate) : transmits traffic at a fixed
rate, such as 64 Kbps voice
• VBR (Variable Bit Rate) : traffic rate is not fixed;
sometimes high, sometimes low, such as MPEG coded
video
Network Design and Analysis-----Wang Wenjie
Introduction: 50
© Graduate University , Chinese academy of Sciences.
Traffic Definition(3)
Traffic Parameters
• Different flows have different traffic patterns
• A given traffic pattern can be described using several
traffic parameters
• Peak rate : maximum rate in any time interval
• Average rate : long term average
• Burst size : duration of peaks
Network Design and Analysis-----Wang Wenjie
Introduction: 51
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Traffic Definition(4)
peak rate
bps
burst
size
average rate
Time
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Introduction: 52
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Traffic Definition(5)
• All patterns have the same average rate (10 Kbps), but
different peak rate and burst size
10 Kbps
time
50 Kbps
100 Kbps
Network Design and Analysis-----Wang Wenjie
Introduction: 53
© Graduate University , Chinese academy of Sciences.
Traffic Definition(6)
• In before example:
Traffic is the number of connections
• In general , the traffic offered to a group of devices
(lines, circuits, links , trunks, or traffic paths) can be
specified by two parameters:
– The average arrival rate 
– The average service time , the reciprocal of  is
referred to as the service rate .
Network Design and Analysis-----Wang Wenjie
Introduction: 54
© Graduate University , Chinese academy of Sciences.
Traffic Definition(7)
• For data networks:
Offered traffic=avg number of packets/time
• For voice(telephone) networks:
Offered load =
(Number of call attempts/hour)*avg call holding time
• This unit is Erlang
One erlang represents a circuit occupied for one hour
• Carried traffic = Offered traffic – lost traffic
Network Design and Analysis-----Wang Wenjie
Introduction: 55