Infobalt’03 Seminaras
Sisteminis tinklų planavimo
metodas bei reikalavimų
analizės rolė
(nuo meno link inžinerijos)
Prof.DrTech. Algirdas Pakštas
London Metropolitan University
Department of Computing, Communications Technology and
Mathematics
a.pakstas@londonmet.ac.uk,
a.pakstas@ieee.org
Infobalt 2003, Vilnius,
2003m. spalio 23d.
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
1
Abstract:
Tutorial looks at the problem of network planning when network is
considered not as collection of separate components but as a
system. Tutorial consists of two parts. The first part of the Tutorial is
devoted to the general overview of the network analysis and design
processes. Network services and services-based networking are
discussed. Systems and network services are presented with more
details. Especial attention is devoted to characterizing of services
including discussion on service requests, service offerings, service
performance requirements, service metrics, as well as reservations
and deadline scheduling. The second part of the Tutorial is focusing
on the concepts of requirement analysis. Description of the
background for requirement analysis is followed by the discussions
on User Requirements, Application Requirements (types of
applications, reliability, capacity, delay, application groups), Host
Requirements (types of host and equipment, performance
characteristics, location information), and Network Requirements
(existing networks and migration, functional requirements, financial
requirements, enterprise requirements).
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
2
Biography:
Prof. Algirdas Pakstas received his M.Sc. in Radiophysics and
Electronics in 1980 from the Irkutsk State University, Ph.D. in
Systems Programming in 1987 from the Institute of Control
Sciences. Currently he is with the London Metropolitan University,
Department of Computing, Communications Technology and
Mathematics where he is doing research in the area of
Communications Software Engineering and is teaching courses
"Network Planning and Management" and "Computer Systems and
Networks". He is active in the IEEE Communications Society
Technical Committees on Enterprise Networking, Communications
Software and Multimedia Communications. He has published 3
research monographs (2 authored and 1 edited) and more than 140
other publications. He is a Senior Member of the IEEE and a
Member of the ACM and the New York Academy of Sciences. He is
currently a member of the Editorial Boards of the following journals
and magazines: IEEE Communications Magazine, Cybernetics and
Systems Analysis, Journal of Information and Organizational
Sciences.
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
3
PART 1: OUTLINE
 A Systems Approach to Network Design
 Introduction - Traditional Network Design
 The Analysis and Design Processes
 Network Services and Services-Based
Networking
 Systems and Network Services
 Systems
 Network Services
 Characterizing Services





Service Requests
Service Offerings
Service Performance Requirements
Service Metrics
Reservations and Deadline Scheduling
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
4
Introduction - Traditional Network
Design
• A kind of art
– Evaluating and choosing network technologies
– Knowing how technologies, services and
protocols work
– Experience in what works and what does not
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
5
Introduction - Traditional Network
Design
• As in other types of art
– Success greatly depends on the person(s) who
is/are doing it
– Designs are rarely reproducible
• Traditional network design is based on developing a
set of pragmatic rules e.g.
• “80/20 rule”
• “bridge when you can, route when you must”
• “throw bandwidth at the problem”
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
6
Introduction - Traditional Network
Design
• It was focusing primarily on capacity planning
• Pragmatic rules worked well with limited choice of
technologies, interconnection strategies, routing
protocols
• Times have changed
– We must adapt design process to the variety of options
– Many new types of services can be offered to the users
– Additionally to the capacity planning we need to consider
optimization of the delay in the network
– Providing reliability is more than just redundant paths in the
network or resilient routing prtocols
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
7
The Analysis and Design
Processes
• Network analysis and design is a combination of
– Design goals
– Trade-offs
• Balance between architecture and function
• Design goals could be such as
– Minimizing network costs
– Maximizing performance
• Trade-offs
– Cost vs. performance
– Simplicity vs. function
– Many ways to achieve design goals - rarely single “right” one
• There are often many wrong ways...
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
8
The Analysis and Design
Processes
• Components of the Analysis and Design Processes
(listed consequently):
– The Systems Approach to Design
– Requirement Analysis
– Flow Analysis
– Logical Design
– Physical Design
– Addressing and Routing
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
9
Network Services and
Services-Based Networking
• There has been significant effort to define and
specify “services” in the ISO/OSI model
• It is a new approach to looking at networking
from the services prospective in the IP-world
• “Services-Based Networking is the concept of
developing network designs that take into
account network services and service support”
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
10
Network Services and
Services-Based Networking
Generations of the network services
Generation
Time Frame
Capability
First
1960s-mid-1980s Basic connectivity/
interoperability
Second
mid-1980sPerformance (IP
early/mid-1990s forwarding rates)
Third (current)
mid-to-late 1990s Network Services
(levels of network
performance and
function)
Fourth
2000-2010
Self-configuration/
administration
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
11
Systems and Network Services:
Systems
 “A network system is the set of components that work
together to support or provide connectivity,
communications, and network services to users of
the system”
 Generic components of a System
| User |
| User |
|Application|
|Application|
| Host |
! Host |
------------------|------(Network)-----|
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
12
Systems and Network Services:
Systems
 Traditional View of a System
----------------------| Host |
| Host |
----------------------|----- (Network) ---|
 Network design have focused on providing
connectivity between hosts
 Systems were described as the set
(host,network)
 and typically did not consider the users or applications
 Thus, there is a need to define more precisely the set
(user, application, host, network)
 Sometime definitions of the “host” and the “network” are not
very much obvious
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
13
Systems and Network Services:
Interfaces and Boundaries
 If the components are known then thethe boundary
condition between them can be set and therefore the
interfaces
 Example:
User
User
Application
Application
Host
Host
Display Parameters
User Interface
API, QoS, ToS
Drivers, Interfaces
Network
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
14
Systems and Network Services:
ATM in Network Backbone
 Example: The picture below is showing the ATM
as a backbone technology
| User |
|Application |
| User |
|Application |
| Host |
| Host |
------------------\-------(x)
NETWORK
(x)--------|
\--[atmX]---[atmX] --/
Here
(x)
- Router
[atmX] - ATM Switch
Here the ATM environment is isolated from the hosts,
applications and users by the routers
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
15
Systems and Network Services:
“Native” ATM Network
 Example: The picture below is showing a “native” ATM network
in which ATM is integrated into the host side
[User]
[User]
[Application]
[Application]
--------------------------------(ATM)---------------------------------
[ATM Specific API]
[ATM Specific API]
[ATM Device Driver]
[ATM Device Driver]
\ [atmX]-[atmX]-[atmX]-[atmX]/
Here
[atmX] - ATM Switch
 Here the ATM is integrated into the host and will interface
directly with the applicaions
 The system is best described as as the set
(user,application, ATM-specific API, ATM device driver, network)
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
16
Systems and Network Services:
Services
• According to the IETF and ATM Forum
– Network Services are sets of network capabilities
that can be configured and managed within the
network
– Network Services are defined
• as levels of performance and function that are
offered by the network, host, and/or application, to
the rest of the system,
• or as sets of requirements that are expected from
the network by the end user, application, or host
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
17
Systems and Network Services:
Services
• Levels of performance are described by the
performance characteristics, e.g.
– capacity
– delay
– reliability
• Functions include
–
–
–
–
–
security
accounting
billing
scheduling
management
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
18
Systems and Network Services:
Services
• Network services: groups of characteristics and
levels
Service Characteristics
Characteristic A \
Characteristic B
}-> Service Level
Characteristic C /
Level A \
…
/
Level B }-> Network Service
|
Level C / Description for Design
V
…
/
Characteristics used to configure services in network and as
service metrics to measure and verify services
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
19
Systems and Network Services:
Service Characteristics
 Service characteristics = Individual network
performance and functional parameters
 Service offering - by the network to the system
 Service request - from the network by users,
applications, or hosts
 Service requirements = characteristics
that are used to gauge the system’s need
for services
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
20
Systems and Network Services:
Service Characteristics
 Service characteristics and requirements are
useful in the network analysis and design
processes:
 In configuring services in network elements (routers,
switches, host operating systems)
 In providing input into the network design
 Need to be described and provisioned end-toend, at all components between end users,
applications and hosts
 Service may fail if some components are not capable to
support it!
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
21
Systems and Network Services:
Service Levels
 Service requirements or characteristics are
grouped together to describe service levels
 Easier to configure, measure and verify service level
instead of a number of individual service characteristics
 Helpful in service accounting and billing
 Service levels can be described with the help of
 Committed Information Rates (CIRs)
 Classes of Services (CoSs)
 Types of Services (ToSs)
 Qualities of Services (QoSs)
 Custom service levels based on groups of individual
service characteristics depending on technology,
protocol, etc.
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
22
Characterizing Services





Service Requests
Service Offerings
Service Performance Requirements
Service Metrics
Reservations and Deadline
Scheduling
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
23
Characterizing Services
Service Requests
 Can be distinguished by the degree of
predictability:
 Best-effort (e.g. best-effort delivery)
 Specified, i.e. deterministic and
guaranteed
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
24
Characterizing Services
Service Requests
 Best-effort:
 No control over how network will satisfy the
service request
 No guarantees are presented
 Network is not obligated to do more than try
 Indicates that the rest of the system
(user, application, host) will need to
adapt to the state of the network at any
given time
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
25
Characterizing Services
Service Requests
 Best-effort:
 Expected service for such requests is
unpredictable and variable
 Such service requests
 Either have no performance requirements
for the network
 Or the requirements are nonspecific
 Consequently service requests are not tuned to
any specific user or application (i.e. very much
universal, generally oriented)
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
26
Characterizing Services
Service Requests
 Specified service requests
 Are based on some knowledge of or control
over the state of the system
 Have more stringent service requirements (i.e.
deterministic and guaranteed) than best-effort
 To support a deterministic service request
by the network the service requirements of
the request must be measurable and
verifiable
 Need for the service metrics
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
27
Characterizing Services
Service Requests
 Specified service requests
 EXAMPLE:
 If service request is made for capacity to be 4-10
Mb/s
 Then there must be
 Way to translate these service requirements into a
service offering from the network
 Way to measure and/or to derive these capacity
characteristics from the network
 Statistical method to control the information flow and
the network to keep this service between the targeted
4-10 Mb/s
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
28
Characterizing Services
Service Requests
 Specified service requests
 Service performance requirements are usually
grouped into service levels
 Service levels can be the same as specified
service requests
 And also can be closely related to well-known
service offerings from the network such as
 ATM QoS
 SMDS CoS
 ...
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
29
Characterizing Services
Service Requests
Specified service requests
 Mapping Service Levels to Service Offerings:
Service Request
Service Performance Requirements
Service Levels (Groups of Requirements)
|
|
|
Service Metrics -------------------------------------------------|
|
|
SMDS CoS
ATM QoS Frame Relay CIR
Service Performance Characteristics
Service Offering
SMDS CoS - Switched Multimegabit Data Service Classes of Service
ATM QoS - Asynchronous Transfer Mode Quality of Service
CIR
- Committed Information Rates
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
30
Characterizing Services
Service Offerings
 Similarly to the Service Requests the
Service Offerings are also grouped as:
 Best-effort
 Specified
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
31
Characterizing Services
Service Offerings
 Best-effort
 Internet is a good example
 Best-effort service offering is compatible with the
best-effort service request
 EXAMPLE:
 File transfer (via FTP) occurs over IP
 FTP uses TCP which via sliding window flow
control mechanism adapts to the current state of
the network it is operating over
 Service requirement from FTP over TCP is best-effort
 Service offering from the Internet is best effort
 During the FTP session the performance characteristics of
the IP network and transport method (TCP) are constantly
adapted
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
32
Characterizing Services
Service Offerings
 Specified (deterministic and guaranteed)
service offerings are:
 Predictable, bounded, or guaranteed
 Specified refers to the network’s ability to
offer a measurable and verifiable service
 Can be low- or high-performance
 Specified service does not imply high performance
 Similarly, ISO 900x quality assurance standards
can not guarantee you a GOOD THING but just a
SPECIFIED QUALITY whatever they mean by it!!!
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
33
Characterizing Services
Service Offerings
 EXAMPLE of Specified Service :
 Network to support real-time telemetry data
 Design goal would be the ability to specify endto-end delay and have the network to satisfy
this delay request
 For example, a service request may be for an end-toend delay of 25ms, with a delay variation of 400s
 This would form the request and the service level (i.e.
QoS level) that needs to be supported by the network
 The network would then be designed to provide a
specified service offering at a QoS level of 25ms endto-end delay and 400s delay variation
 The delay and delay variation would then be measured
and verified with service metrics (using tools such as
ping or tcpdump, or with custom one)
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
34
Characterizing Services
Service Offerings
 Service Requests and Offerings
Service Request
|
|
Best-Effort
Deterministic/Guaranteed
|
|
| Service Performance Characteristics/Levels
|
| | |
Service Metrics -------------------------------------------------------|
| | |
| Service Performance Characteristics/Levels
|
|
Best-effort Deterministic/Guaranteed
|
|
Service Offering
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
35
Characterizing Services
Service Performance Requirements
 Service Performance Requirements
 Reliability, Capacity and Delay
 are related to each other
 Reliability:
 Definition by the J.D.McCabe:
 “Reliability is a measure of the system’s ability to
provide deterministic and accurate delivery of
information...”
– IT CAN BE ARGUED THAT RELIABILITY IS ONLY THE
GUARANTEE OF ACCURACY WITH NO TIME CONSTRAINTS
– DIFFERENT DEFINITION OF RELIABLITY MAY LEAD TO
BUILDING DIFFERENT CONCEPTS WHICH BETTER
REFLECT A REAL WORLD VIEW TO THE SYSTEM’S DESIGN
©2003 Algirdas Pakštas
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36
Characterizing Services
Service Performance Requirements
 Capacity
 “It is a measure of the system’s ability to transfer
information”
 This term is often used intechangeably with
bandwidth, throughput and goodput
 Bandwidth is sometime described as theoretical
capacity what is not strictly correct (remember
Nyquist’s and Shannon’s equations?)
 Throughput is the realizable capacity of the system or
its components or elements
 SONET OC-3c circuit is designed to achieve data rate
155.52 Mb/s = 3x51.84 Mb/s (i.e. 3xOC-1 circuits)
 Practically achievable throughput is ~80-128 Mb/s
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
37
Characterizing Services
Service Performance Requirements
 Delay
 “It is a measure of the time which is taken for the
transmission of the single unit of information (bit,
byte, cell, frame, packet) across the system”
 Often used are propagation, transmission, queueing,
and processing delays
 End-to-end and round-trip delays are useful
measurements
 Delay represents microscopic view of network
behaviour
 Latency can be defined as an overall delay caused by
the application processing and task completion times
 Latency represents macroscopic view of network behaviour
©2003 Algirdas Pakštas
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38
Characterizing Services
Service Performance Requirements
 Performance Envelops
 Useful for visualizing the regions of
performance in which the network will be
expected to operate
 Service performance requirements can be
mapped from the applications onto such
environments in order to show relative
performance of each application
 EXAMPLES:
 2-D Service Performance Envelop describing Capacity,
Data Size and End-to-end Delay
 3-D Service Performance Envelop including Reliability
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
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Characterizing Services
Service Performance Requirements
2-D Service Performance Envelop describing
Capacity, Data Size and End-to-end Delay
©2003 Algirdas Pakštas
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Characterizing Services
Service Performance Requirements
3-D Service Performance Envelop including Reliability
 Note low-performance and high-performance regions!
©2003 Algirdas Pakštas
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41
Characterizing Services
Service Metrics
 Service metrics are intended to be
measurable
 Can be used to establish reference levels
(a combination of service metrics for
reliability, capacity and delay) for service
performance
 3 types of reference levels:
 Service thresholds
 Service boundaries
 Service guarantees
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
42
Characterizing Services
Service Metrics
 Service thresholds - discriminators used on
applications to distinguish between highperformance and low-performance service
 Service boundaries - combinations of lowand/or high-performance levels used to
predict a service level for an application
 Service guarantees - strict performance
levels. If they are not met it may cause some
type of action from the system (such as
policing)
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
43
Characterizing Services
Service Metrics
 Reference levels are described in terms of
service metrics for the system
 EXAMPLE: System using SNMP has MIB
variables for each network element
 We may choose:
 A reference level of the amount of the capacity
being utilized
 A service metric of the number of bytes in or out of
each interface of the network elements
 MIB variables of ifInOctets and ifOutOctets
©2003 Algirdas Pakštas
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44
Characterizing Services
Service Metrics
Example of Reference Levels-Service Thresholds
Threshold
|
App3 App6
|
App5
App2
App1
|
App4
--------------------|--------------->
Service
Low Capacity
|
High Capacity
Threshold
Expected/Predicted Application Capacities
©2003 Algirdas Pakštas
Sisteminis tinklų planavimo metodas bei reikalavimų analizės rolė (nuo meno link inžinerijos)
45
Characterizing Services
Service Metrics
Example of Reference Levels Boundaries and Guarantees
©2003 Algirdas Pakštas
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46
Characterizing Services
Reservations and Deadline
Scheduling
 Some applications may be operating in
real-time
 Session may be not active until time T
 Resources for this application are not
required until time T and can be used for
something else
 Application may have a deadline when all
tasks must be completed
 May need prioritizing of the use of network
resources for this application
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Conclusions for PART 1
 It is very important to take a system’s
approach to network design
 System = (user, application, host, network)
 System is offering services to the end
users/customers
 In order to implement services and and
achieve their characteristics we need to
quantify requirements
 Requirements Analysis is the next step
in the network analysis process:
 To gather, analyze, and understand the
requirements from the system
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PART 2: OUTLINE
 Requirements Analysis: Concepts
 Background for Requirement Analysis
 User Requirements
 Application Requirements





Types of Applications
Reliability
Capacity
Delay
Application Groups
 Host Requirements
 Types of Host and Equipment
 Performance Characteristics
 Location Information
 Network Requirements




Existing Networks and Migration
Functional Requirements
Financial Requirements
Enterprise Requirements
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Background for Requirement
Analysis
 Requirement Analysis helps to understand
design environment
 Consists of
 Identifying, gathering, and understanding system
requirements and their characteristics
 Developing thresholds for performance to
distinguish between low- and high-performance
services
 Determining specified services for the network
 Requirement Analysis is fundamental to the
network design process but is often
overlooked or ignored
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Background for Requirement
Analysis
 Gathering requirements means talking to
users and network personnel and
interpreting the results
 Each user has its own set of requirements
 Network personnel are often distanced from the
users and do not have clear idea of what users
want or need
 Thus it is a difficult part of the design process
 Not doing it may lead to the solutions which
are not those which the users and
applications may need
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Background for Requirement
Analysis
EXAMPLES:
 Design is based on a particular technology,
typically on the most comfortable for the
designer
 Design is based on a particular vendor…
 This happens due to the budget constraints and
deadlines which are forcing to use familiar, easy
to apply technologies
 Problem is that such designs are not objective
 Familiar technologies, protocols or vendors may
be poor choices for that particular environment
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Background for Requirement
Analysis
 The results of the Requirement Analysis are
 Requirements Specification
 Application Map
 Requirements Specification is a series of
worksheets that list the requirements
gathered for the design
 Application Map shows the location
dependencies between applications
 Will be used for Flow Analysis
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User Requirements
 The user component of the generic system
and the interface:
[ User ]
[ User ] /Timeliness
---------------------------------------< Interactivity
[Application]
[Application] \Reliability
[ Host ]
[ Host ]
------------------\----(Network)-----/
Quality
Adaptability
Security
Affordability
User Numbers
User Locations
Expected Growth
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User Requirements
Timeliness
 “Timeliness is a requirement that the user is
able to access, transfer, or modify
information within a tolerable time frame”
 What is “tolerable” depends on the user’s
perception of the delay in the system
 EXAMPLES-delays that network will need to
provide:
 User wants to download files from a server and
complete each transfer in 10 minutes
 User wants to receive video frames every 30ms
 End-to-end or round-trip delay is important
measurement
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User Requirements
Interactivity
 Similar to “timeliness” but focuses on a
response time from the system or network
 Interactivity is to be looked as an indication
of the response time which are on the order
of the human response times
 “Interactivity is a measure of the response
time of the system when it is required to
actively interact with a human”
 The round-trip delay is a measure of the
interactivity
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User Requirements
Reliability
 From the user prospective it is a requirement
for constantly available service
 Possibility to have access to system resources a
very high percentage of time
 Consistent level of service to the user in terms of
network performance
 Thus, reliability as requirement is closely related
to the performance characteristic reliability where
delay and capacity are also important
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User Requirements
Quality
 Refers to the quality of the presentation to
the user
 Perception of audio, video and/or data displays
 EXAMPLE: Providing videoconferencing,
videofeeds and telephony
 It is possible to do it on the Internet!
 But other technologies can provide much better
presentation quality
 It is often not sufficient to provide just a capability
over a network
 Measures of quality should include all the
performance characteristics
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User Requirements
Adaptability
 “It is ability of the system to adapt to the
user’s changing needs”
 EXAMPLES:
 Distance-independence
 Relying on the network
 Coupling to the logical servers and decoupling from
the physical - it does not matter where the servers
are as long as users can get services
 As a result user may lose a part of his rights - the
ability to know where the job was executed
 Mobility
 Mobile computing, access to the services and
resources from any location via portable computers
and ad-hoc access to the network
 Adaptability must be reflected in the system
design
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User Requirements
Security
 It is a requirement to guarantee
 Integrity (accuracy and authenticity) of the user’s
information and physical resources
 Access to the user’s and system resources
 Security is probably closest to the
performance characteristic reliability
 It impacts capacity and delay
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User Requirements
Affordability
 It is the last general user requirement
 “We would like to have it but how much does it
cost?”
 Not technical but will impact the network design!
 We have to look at the user/customer
budget
 Are design costs too expensive to implement?
 How cost and funding are tied to users or groups
of users?
 Funding should be discussed as a system-wide
requirement from the overall budget perspective
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Application Requirements
 We will look at
 Types of Applications




Reliability
Capacity
Delay
Application Groups
[ User ]
[ User ]
[Application]
[Application]
[ Host ]
[ Host ]
------------------\----(Network)-----/
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Application Requirements
Types of Applications
 Service and service performance
requirements of the applications can be
characterized as:
 Mission-critical applications
 Deterministic and/or guaranteed reliability
 Controlled-rate applications
 Specified capacity
 Real-time/interactive applications
 Specified delay
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Application Requirements
Types of Applications
User Service and Performance Requirements
Timeliness \_________________ / DELAY
Interactivity /
\
Reliability \
/
Quality
\__________________/ RELIABILITY
Adaptability /
\
Security
/
\
Affordability
\
/
User Numbers
\_____________/ CAPACITY
User Locations
/
\
Expected Growth /
\
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Application Requirements
Reliability
 Reliability can be subjective but some
applications must maintain high reliability in
order to function
 Loss of reliability can result in
 Loss of revenue or customers
 Typical application: transaction/money dependant,
investment banking or airline reservation system
 Unrecoverable information or situation
 Telemetry processing and teleconferencing applications
 Loss of sensitive data
 Customer ID/billing and intelligence-gathering
applications
 Loss of life
 Transportation or health-care monitoring applications
 QUESTION: Can the Best-Effort System be at all suitable
for the mission-critical applications?
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Application Requirements
Capacity
 Could be required by the applications having
well understood amount of capacity
 EXAMPLE: Controlled-rate applications
 Voice, non-buffered video, some teleservice
applications
 May require to define:





Thresholds
Bounds
Guarantees on minimum capacity
Peak capacity
Sustained capacity
 Can be tied to the end-to-end delay of the
network
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Application Requirements
Delay
 Optimizing the total (end-to-end and roundtrip) delay is the most important for the
application service
 Need for “better than the best-effort”
services
 Applications with delay requirements are
migrating to the Internet or IP intranets
 Applications previously dedicated to a single
user/host are used via Internet/intranet
 Term “real-time” describes the need for strict
delay tolerance
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Application Requirements
Delay
Real-time applications
 Have the most strict timing relationship
between source and destination
 Timers are set for the receipt of information
 If information is received after the timers expire it is
considered worthless and is dropped
 Does not mean that information has to be
transferred within predefined time, rather
 Delay boundaries (and, hopefully, consequences)
are understood by source and destination
 Destination does not wait beyond this boundary
 EXAMPLE: Video playback - delay beyond the
playback timer can cause blank parts in frames
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Application Requirements
Delay
Non-real-time applications
 Various end-to-end delay requirements
 Destination will wait until the information is
received (defined by the timers in
applications and hosts)
 Majority of the applications are non-real-time
 Can be
 Interactive
 Asynchronous
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Application Requirements
Delay
Interactive applications
 Assume timing relationship between source
and destination
 Typical applications: telnet, FTP, Web
Asynchronous applications
 Intensive to time
 Assumes no timing relationship
 EXAMPLE: E-mail
 Can be
 Burst
 Bulk
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Application Requirements
Delay
Application Delay Types
Real Time|
Non-Real-Time
|
/
\
|Interactive |Asynchronous
|
/ \
|
|Burst | Bulk |Time-Intensive
-------------------------------------Telemetry|Telnet| FTP |E-mail
Processing
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Application Requirements
Application Groups
 It is useful to group together the
applications with similar performance
characteristics
 Helps in mapping performance characteristics
 Helps in gathering requirements
 Groups may have some overlap…
 EXAMPLES of the groups are discussed
below
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Application Requirements
Application Groups
 Command and control/telemetry applications
 Information is transmitted between remote objects
 Characterized as having high-performance delay and
reliability
 Possibly mission-critical and/or real-time applications
 Visualization applications
 Viewing and manipulation of 2-D, 3-D and VR objects
 Characterized as having high-performance capacity and
delay
 Possibly real-time and/or controlled-rate applications
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Application Requirements
Application Groups
 Distributed computing applications
 Different variants of the processor coupling
 Share the same local bus
 Co-located at the same LAN (computing cluster)
 Distributed across LAN, MAN, and WAN boundaries
 Degree of distribution/parallelism is also
determined by the granularity of the task
 Characterized as having high performance delay
 Possibly being interactive applications
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Application Requirements
Application Groups
 Applications for Web access, development and
use
 Involves accessing remote host and
downloading/uploading information
 Web-sessions are
 Interactive
 Amounts of information are small
 Characterized as being delay-sensitive but NOT highperformance
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Application Requirements
Application Groups
 Bulk data transport
 Typically file transfer (FTP)
 Optimization of the data transfer rate at the
expense of interactivity
 Characterized as being not high-performance
 Tele-service applications
 Teleconferencing, telemedicine, teleseminars,…
 Simultaneous delivering of mixture of the data, voice,
and video to the groups of people at various locations
 EXAMPLE: Multicast backbone (mbone) on the Internet
 Characterized as having high-performance
capacity, delay, and/or reliability, depending on
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Application Requirements
Application Groups
 Operations, administration, and maintenance
(OAM) applications
 Needed for proper functioning and operation of
the network







Domain name service (DNS)
Mail service/SMTP
News services/NNTP
Address resolution service (ARP)
Network monitoring and management
Network security
Systems accounting
 Generally requires high reliability
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Application Requirements
Application Groups
Application Component Interface to System
[ User ]
[ User ]
/Application
|
|
/ Group
[Application] [Application] / Application
-----------------------------------------< Type
[ Host ]
[ Host ]
| Application
------------------| Performance
\----(Network)-----/
| Characteristics
|Application
| Locations
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Host Requirements
Host Component of the Generic System
[ User ]
[ User ]
|
|
[Application]
[Application]
|
|
[ Host ]
[ Host ]
------------------\----(Network)-----/
 We will look at
 Types of Host and Equipment
 Performance Characteristics
 Location Information
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Host Requirements
Types of Host and Equipment
 Generic computing devices
 Dos-, Windows-based PCs, Macs, Unix workstations,
etc.
 Form access points into the network for [single] user
 Important from end-to-end perspective
 Tend to be overlooked
 Creates “last foot” problem in systems performance
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Host Requirements
Types of Host and Equipment
 Servers
 More powerful
 Computing servers, storage servers, application
servers, etc.
 Also have requirements for “last foot” performance
 Requirements specific to the server’s role
 Specialized Equipment
 Supercomputers, mainframes, parallel or
distributed computing systems, sensors, data
acquisition devices, etc.
 Tends to be location-dependent
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Host Requirements
Types of Host and Equipment
Specialized Equipment Tends to be Location-Dependent
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Host Requirements
Performance Characteristics
 Performance of the components impacts the
overall performance of the server/host
Operating
System
Processing
Memory
System Bus
Network
Interface
Disk Drive
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Other
Peripherals
83
Host Requirements
Performance Characteristics
 Performance of the components end-to-end in
the host is important
 Storage performance
 Disk-drive seek time
 Tape performance
 Processor (CPU) performance
 Memory performance
 Access time
 System bus performance
 Capacity and arbitration mechanisms
 Effectiveness of Software
 Driver
 OS (effectiveness of the protocol stack)
 Number of memory copies in the protocol stack
 Cost of execution of a given OS
 API
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Host Requirements
Location Information
 Helps to determine
 Relationships between components
 Flow characteristics
 Particularly important
 In the outsourcing of system components or
functions
 In the consolidation of organizations,
components or functions
 In the relocation of system components or
functions within an organization
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Host Requirements
System Components can have Location Dependencies
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Host Requirements
Summary of the Host/Network
Interface
Host Component Interface to System
[ User ]
[ User ]
/Types of
|
|
/ Hosts and
[Application]
[Application] / Equipment
|
|
/
[ Host ]
[ Host ] / Location
------------------- / Information
---------|----------------------|------<
\----(Network)----/
\ Host/Equipment
\
\
Performance
Characteristics
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Network Requirements
 Existing Networks and Migration
 Functional Requirements
 Financial Requirements
 Enterprise Requirements
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Network Requirements
Existing Networks and Migration
Network Component Interface to System
[ User ]
[ User ]
/-Scaling
|
|
/
[Application]
[Application] / -Interoperability
|
|
/
[ Host ]
[ Host ]
/ -Location Information
------------------/
|
|
/
-Network Services
(
Network
)--<
:…....(<Existing Network> )...: \
-Support Services
:
/
: \
:...<Existing Network>…....:
\ -Network Performance
\ Characteristics
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Network Requirements
Functional Requirements
 Requirements for Network Management and
Security
 Categories of network management tasks
 Monitoring (automatic?)
 For event notification (frequent snapshot of the system)
 For metrics and planning (large archives)
 Actions (manual?)
 Network configuration
 Troubleshooting
 Monitoring:
 Obtaining values for network management parameters
from network elements
 Processing the data
 Visualization
 Archiving the data
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Network Requirements
Functional Requirements
 General Network Management Requirements
 Monitoring methods
 Instrumentation methods








Protocols (SNMP, SNMPv2/v3, CMIP, RMON)
Parameter lists (MIBs)
Monitoring tools
Direct access
The characteristics sets for monitoring
In-band vs. out-of-band monitoring
Centralized vs. distributed monitoring
Performance requirements
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Network Requirements
Functional Requirements
 Developing a security plan for the network:
 User requirements
 Security policies
 Risk analysis
 User Requirements for Security
 Government specified requirements: MoD/DoD/DoE...
 Organization-specified security requirements
 End-user-specified security requirements
 May be applied to
 Users/User groups
 Projects
 Specific types of data (also how data are generated,
transferred, processed and stored)
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Network Requirements
Financial Requirements
 Level of funding for implementing network
design is system-wide requirement
 Funding is associated with
 Overall cost limit
 Recurring components
 Expected to occur or be replaced/upgraded periodically
 Operations, administrations and maintenance, costs
from service providers, provisions for network
modification
 Non-recurring components - building of the
network




Network design
Network deployment
Hardware/Software components
Initial installation or establishment of any services from
service providers
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Network Requirements
Enterprise Requirements
 Enterprises need transfer of
 Phone/voice
 FAX
 Video
 Enterprise environment presumes integration
of such services into a common transmission
infrastructure
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Requirement Analysis
Conclusions
The Process Model for Requirement Analysis
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Bibliography
• James D. McCabe: “Practical Computer
Network Analysis and Design”, Morgan
Kaufmann Publishers, San Francisco, USA,
1998. ISBN 1-55860-498-7
• Algirdas Pakštas: Raspredelennye
programmnye konfiguracii: Analiz i razrabotka
(“Distributed Software Configurations: Analysis
and Development”), Mokslas, Vilnius, 1989.
ISBN 5-420-00637-5
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