network design and analysis-----wang wenjie introduction: 1 © graduate university, chinese academy...
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Network Design and Analysis-----Wang Wenjie Introduction: 1
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Network Design and
Performance Analysis
Wang Wenjie
Network Design and Analysis-----Wang Wenjie Introduction: 2
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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
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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
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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 Introduction: 5
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Course Agenda
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 Introduction: 6
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Course Information
• Who is the course for?
– Graduate Students
• Grading
– Homework:• Assignments • Programming
– Final Exam :
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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 0-387-95037-0).
Network Design and Analysis-----Wang Wenjie Introduction: 8
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Introduction
Network Design and Analysis-----Wang Wenjie Introduction: 9
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Outlines
• Network Models
• Methods for Performance Evaluation
• Quality of Service(QoS)
• Traffic Definitions
Network Design and Analysis-----Wang Wenjie Introduction: 10
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Outlines
• Network Models
• Methods for Performance Evaluation
• Quality of Service(QoS)
• Traffic Definitions
Network Design and Analysis-----Wang Wenjie Introduction: 11
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Network Models
• What are we modeling?
• Networks (broadly defined) generally fall into one of three categories
– Resource sharing networks– Process networks– Switching networks
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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 Introduction: 14
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Process networks(1)
Network Design and Analysis-----Wang Wenjie Introduction: 15
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Process networks(2)
Network Design and Analysis-----Wang Wenjie Introduction: 16
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Switching networks(1)
Network Design and Analysis-----Wang Wenjie Introduction: 17
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Switching networks(2)
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Outlines
• Network Models
• Methods for Performance Evaluation
• Quality of Service(QoS)
• Traffic Definitions
Network Design and Analysis-----Wang Wenjie Introduction: 19
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Life Cycle
Performance Evaluation/Analysis
Network Design
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
Network Design and Analysis-----Wang Wenjie Introduction: 21
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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
Network Design and Analysis-----Wang Wenjie Introduction: 22
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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
Network Design and Analysis-----Wang Wenjie Introduction: 23
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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
Network Design and Analysis-----Wang Wenjie Introduction: 24
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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
Network Design and Analysis-----Wang Wenjie Introduction: 25
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Example: ISP(1)
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Example: ISP(2)
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Example: ISP(3)
Network Design and Analysis-----Wang Wenjie Introduction: 28
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Example: ISP(4)
Network Design and Analysis-----Wang Wenjie Introduction: 29
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Example: ISP(5)
Network Design and Analysis-----Wang Wenjie Introduction: 30
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Example: ISP(6)
Network Design and Analysis-----Wang Wenjie Introduction: 31
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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 Introduction: 32
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Outlines
• Network Models
• Methods for Performance Evaluation
• Quality of Service(QoS)
• Traffic Definitions
Network Design and Analysis-----Wang Wenjie Introduction: 33
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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
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Quality of Service(2)
Important Performance ParametersSystem BlockingDelay in the messagingJitterBuffer OverflowPacket LossSystem ReliabilityEnd-to-end delay in media packetsResponse DelaySystem Recovery TimeAdmission Control AlgorithmResource Scheduling algorithmsSystem CapacitySystem Engineering Rules
Simulation &Queuing Theory
Capacity
Game Theory
Network Design and Analysis-----Wang Wenjie Introduction: 35
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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 Introduction: 36
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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 Introduction: 37
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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 Introduction: 39
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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: 40
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Outlines
• Network Models
• Methods for Performance Evaluation
• Quality of Service(QoS)
• Traffic Definitions
Network Design and Analysis-----Wang Wenjie Introduction: 41
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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 Introduction: 42
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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: 43
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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
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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 Introduction: 45
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Example of traffic system ( 2 )
Morning(M) Afternoon(A) Evening(E)
AB 5 11 8
AC 6 13 6
BC 10 2 7
A C
B
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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:
Network topologyCapacity links and switchesRouting
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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?
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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: 49
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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
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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
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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: 52
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Traffic Definition(4)
peak rate
average rateburst size
Time
bps
Network Design and Analysis-----Wang Wenjie Introduction: 53
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Traffic Definition(5)
• All patterns have the same average rate (10 Kbps), but different peak rate and burst size
time
100 Kbps
50 Kbps
10 Kbps
Network Design and Analysis-----Wang Wenjie Introduction: 54
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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: 55
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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