Network analysis and design unite_-i.ppt

UNIT – I
NETWORK ANALYSIS ARCHITECTURE
AND DESIGN
1

Network Design
• Through the Kurose text we’ve covered
– The application, transport, network, & link layers
– Wireless and multimedia technologies
– Security
– Network management
• Not bad!
• So how does all this come together to help
create a network?
INFO 331 Network Design 2

Network Design
• Ok, that’s not a small question – we’ll just
tickle the surface (not even scratch!)
• Main resources for this section are:
– McCabe, James D. (2003). Network Analysis,
Architecture & Design (2nd Ed.). San Francisco:
Morgan Kaufmann Publishers. [Chapters 1-5, 10]
– Teare, Diane. (2004). CCDA Self-Study: Designing
for Cisco Internetworking Solutions (DESGN).
Indianapolis: Cisco Press.

Network Design Objective
• Ultimately, our network design must answer
some pretty basic questions
– What stuff do we get for the network?
– How do we connect it all?
– How do we have to configure it to work right?
• Traditionally this meant mostly capacity
planning – having enough bandwidth to
keep data moving
– May be effective, but result in over engineering

Network Design Objective
• And while some uses of the network will need
a lot of bandwidth (multimedia), we may also
need to address:
– Security
• Considering both internal and external threats
– Possible wireless connectivity
– Reliability and/or availability
• Like speed for a car, how much are you willing
to afford?

Network Design Phases
• Designing a network is
typically broken into three
sections:
– Determine requirements
– Define the overall
architecture
– Choose technology and
specific devices
(McCabe, 2003)

Systems Methodology
• There’s lots of room for refining these sections
(Teare, 2004)
– Identify customer requirements
– Characterize the existing network
– Design topology
– Plan the implementation
– Build a pilot network
– Document the design
– Implement the design, and monitor its use

Two Main Principles
• For a network design to work well, we need to
balance between
– Hierarchy – how much network traffic flows
connect in tiers of organization
• Like tiers on an org chart, hierarchy provides separation
and structure for the network
– Interconnectivity – offsets hierarchy by allowing
connections between levels of the design, often
to improve performance between them

Two Main Principles
(McCabe, 2003)

SERVICE REQUESTS AND
REQUIREMENTS
• They are identified by the degree of
predictability needed from the service by the
users, applications or devices
10
Best of effort Predictable Guarenteed

Best Of Effort Service
• No control over how the network will satisfy the
service requests
• Indicates that the rest of the system will have to
adapt to the state of the network at any given time
• Services will be both un-predictable and unreliable
• Variable performance across a range of values
• No specific performance requirements

GUARANTEED SERVICE
• These services are predictable and reliable
• They imply a contract between the user and
the provider
• When the contract is broken the provider is
accountable and must account for loss of
service and compensate the user.

Predictable services
• These services fall in between best of effort and guaranteed
services
• They offer some degree of predictability and yet are not
accountable .
• Predictable and guaranteed are based on some prior
knowledge of and control over the state of the system
• These services must have clear set of service requirements
• These requirements must be configurable , measurable and
verifiable
• Ex: a bandwidth of 4-10 mbps. We should be able to
communicate this request, measure / derive the level of
resources needed and then determine whether the resources
are actually available

Ex: performance of a 100mbps FE connection.

SERVICE METRICS
• (i) Threshold values: is a value for a
performance characteristic that is a boundary
between two regions of conformance
• (ii) limit: is a boundary between conforming
and non conforming regions and is taken as
an upper or lower limit for a performance
characteristic.
• Limits are more dangerous than thresholds
and result in severe actions

Requirements
• Service
requirements could
include the QoS
(quality of service)
guarantees (ATM,
Intserv, Diffserv,
etc.)
– This connects to
network
management
monitoring of
network
performance
16

Performance Characteristics
Capacity Delay RMA

Capacity
• Is a measure of the systems ability to transfer
information
• Bandwidth, throughput and goodput are the
terms associated with it.

DELAY
• Is the time difference in the transmission of
information across the system.
• Sources of delay (i) propagation delay (ii)
transmission delay (iii) queuing and
processing delay
• Measures of delay( i) end-end delay (ii) RTT
(iii) latency (iv) Delay Variation

RMA Reliability
• Is a statistical indicator of the frequency of
failures of the network and its components
• Reliability also requires some degree of
predictability. The delivery of information
must occur within well known time
boundaries.
• When delivery time varies greatly , the
confidence in the network is lost and hence is
considered less reliable

Maintainability
• Is a statistical measure of the time to restore the
system to fully operational mode after it has
experienced a fault
• Generally expressed as
(i) MTTR (mean time to repair) : total time taken for
detection, isolation of the failure to a component
that can be replcaed, Delivery of necessary partsnto
the location of the failed component (logistic
time),replca the component, test it and restore full
service

Availability
• Is a relationship between the frequency of
mission critical failures and the time to restore
service
• A= MTBF/ (MTBF +MTTR)
• MTBF = mean time between failures
• MTTR = mean time to repair
• A= availability

Performance envelope
• Is a combination of two or more performance
requirements, with thresholds and upper and
lower limits for each

Network supportability
• The 80/20 rule applies here
– 80% of the cost of a network is its operation
and support
– Only 20% is the cost of designing and
implementing it
• So plan for easy operation, maintenance, and
upgrade of the network

Post Implementation of the network
life cycle
• Phase 1: operation: The network and the systems are
properly operated and managed and required
maintenance are identified
• Phase 2 : Maintenance: Preventive and corrective
maintenance and the parts, tools plans and
procedures for accomplishing this task
• Phase 3: Human knowledge : Documentation,
training and skilled person required to operate and
maintain the system

Key characteristics that Affect post
implementation cost
• Network and system Reliability
• Network and system Maintainability
• Training of the operators to stay within
operational constraints
• Quality of the staff required for maintenance
actions

Requirements? Booooring!
• Yes, determining the requirements for a
network probably isn’t as much fun as
shopping for really expensive hardware
– And that may be why many networks are poorly
designed – no one bothered to think through
their requirements!
– Many people will jump to a specific technology or
hardware solution, without fully considering other
options – the obvious solution may not be the
best one

Requirements
• We need to develop the low level design and
the higher level architecture, and understand
the environment in which they operate
• We also need to prove that the design we’ve
chosen is ‘just right’ (Southey, 1837)
– Is that $2 million network backbone really enough
to meet our needs?
– How do we know $500,000 wouldn’t have been
good enough?

Requirements
• Part of this process is managing the
customer’s expectations
– They may expect a much simpler or more
expensive solution than is really needed
– Showing analysis of different design options,
technologies, or architectures can help prove
you have the best solution

Requirements
• We need to use a systems approach for
understanding the network
– The system goes far beyond the network
hardware, software, etc.
– Also includes understanding the users,
applications or services, and external environment
• How do these need to interact?
• What does the rest of the organization
expect from the network?

Requirements
• Consider how devices communicate
Images from (McCabe, 2003)
unless noted otherwise

Requirements
• What services are expected from the
network?
– Typical performance levels might include capacity,
delay time, reliability
• Providing 1.5 Mb/s peak capacity to a remote user
• Guaranteeing a maximum round-trip delay of 100 ms to
servers in a server farm
– Functions include security, accounting, scheduling,
management
• Defining a security or privacy level for a group of users
or an organization

Requirements
• Capacity refers to the ability to transfer data
– Bandwidth is the theoretical capacity of some part
of the network
– Throughput is the actual capacity, which is less
than the bandwidth, due to protocol overhead,
network delays, etc.
• Kind of like hard drive actual capacity is always less
than advertised, due to formatting

Requirements Analysis
• Given these concepts, how do we describe
requirements for a network?
• Need a process to filter or classify
requirements
– Network requirements (often have high, medium,
low priorities)
– Future requirements (planned upgrades)
– Rejected requirements (remember for future ref.)
– Informational requirements (ideas, not required)

Requirements Analysis
• Requirements can come from many aspects of
the network system
– User Requirements
– Application Requirements
– Device Requirements
– Network Requirements
– Other Requirements

User Requirements
• User requirements are
often qualitative and
very high level
– What is ‘fast enough’
for download? System
response (RTT)?
– How good does video
need to be?
– What’s my budget?

Application Requirements
• What types of apps are we using?
– Mission-critical
– Rate-critical
– Real-time and/or interactive
• How sensitive are apps to RMA (reliability,
maintainability, availability)?
• What capacity is needed?
• What delay time is acceptable?

• What groups of apps are being used?
– Telemetry/command and control - remote devices
– Visualization and simulation
– Distributed computing
– Web development, access, and use
– Bulk data transport – FTP
– Teleservice – VOIP, teleconference
– Operations, admin, maintenance, and provisioning
(OAM&P) – DNS, SMTP, SNMP
– Client-server – ERP, SCM, CRM

• Where are the
apps located?
• Are some only
used in certain
locations?

Device Requirements
• What kinds of devices are on your network?
– Generic computing devices include normal PCs,
Macs, laptops, handheld computers, workstations
– Servers include all flavors of server – file, print,
app/computation, and backup
– Specialized devices include extreme servers
(supercomputers, massively parallel servers), data
collection systems (POS terminals), industry-
specific devices, networked devices (cameras,
tools), stoplights, ATMs, etc.

Device Requirements
• Specialized
devices are
often location-
specific

Device Requirements
• We want an understanding of the device’s
performance – its ability to process data from
the network
– Device I/O rates
– Delay time for performing a given app function

Device Requirements
• Performance results from many factors
– Storage performance, that is, flash, disk drive,
or tape performance
– Processor (CPU) performance
– Memory performance (access times)
– Bus performance (bus capacity and arbitration
efficiency)
– OS performance (effectiveness of the protocol
stack and APIs)
– Device driver performance

Device Requirements
• The device locations
are also critical
– Often generic
devices can be
grouped by their
quantity
– Servers and
specialized stuff are
shown individually

Network Requirements
• Network requirements (sounds kinda
redundant) are the requirements for
interacting with the existing network(s) and
network management concerns
• Most networks have to integrate into an
existing network, and plan for the future
evolution of the network

• Issues with network integration include
– Scaling dependencies – how will the size of the
existing network affect the new one?
• Will the existing network change structure, or just add
on a new wing?
– Location dependencies – interaction between old
and new networks could change the location of
key components
– Performance constraints – existing network could
limit performance of the new one

– Network, system, and support service
dependencies
• Addressing, security, routing protocols and network
management can all be affected by the existing
network
– Interoperability dependencies
• Changes in technology or media at the interfaces
between networks need to be accounted for, as well as
QoS guarantees, if any
– Network obsolescence – do protocols or
technologies become obsolete during transition?

• Network management and security issues
need to be addressed throughout
development
– How will the network be monitored for events?
– Monitoring for network performance?
• What is the hierarchy for management data flow?
– Network configuration?
– Troubleshoot support?

• Security
analysis can
include the
severity
(effect) of an
attack, and
its
probability of
occurrence
Effect/ Probability User Devices Servers Network Software Services Data
Unauthorized Access B/A B/B C/B A/B B/C A/B
Unauthorized Disclosure B/C B/B C/C A/B B/C A/B
Denial of Service B/B B/B B/B B/B B/B D/D
Theft A/D B/D B/D A/B C/C A/B
Corruption A/C B/C C/C A/B D/D A/B
Viruses B/B B/B B/B B/B B/C D/D
Physical Damage A/D B/C C/C D/D D/D D/D
Effect: Probability:
A: Destructive C: Disruptive A: Certain C: Likely
B: Disabling D: No Impact B: Unlikely D: Impossible

Other Requirements
• Requirements can come from other outside
sources – your customer, legal requirements,
larger scale organization (enterprise)
requirements, etc.
• Additional requirements can include
– Operational suitability – how well can the
customer configure and monitor the system?
– Supportability – how well can the customer
maintain the system?

Other Requirements
– Confidence – what is the data loss rate when the
system is running at its required throughput?
• Financial requirements can include not only
the initial system cost, but also ongoing
maintenance costs
– System architecture may be altered to remain
within cost constraints
• This is a good reason to present the customer with
design choices, so they see the impact of cost
versus performance

Other Requirements
• Enterprise requirements typically include
integration of your network with existing
standards for voice, data, or other protocols

Requirements Spec and Map
• A requirements specification is a document
which summarizes the requirements for (here)
a network
– Often it becomes a contractual obligation, so
assumptions, estimates, etc. should be carefully
spelled out
• Requirements are classified by Status, as
noted earlier (core/current, future, rejected,
or informational requirement)

Requirements of an Company
• 1building must .150 users (60 engineers, 15 HR, and finance, 30 manufacturing 10
management, 30 sales/marketing, 5 others)
• Each area in building the support fast ethernet connection to the backbone
• Database ,visualisation Manufacturing, and payroll applications are considered
mission critical
• Inventory applications are not determined at this time
• Database applications require a min. of 150kbps
• Engineering users have a workstation with gigaE NICs
• Visualisation applications for finance require 40Mbps capacity and 100ms round
trip delay
• Payroll apps require 100% up time
• Company must be secure from internet attack
• Company requires a min. of T! access to internet

Requirements Specification
ID/Name Date Type Description Gathered/Derived Locations Status Priority
 Priority can provide additional numeric
distinction within a given Status (typically
on a 1-3 or 1-5 scale)
 Sources for Gathering requirements can be
identified, or give basis for Deriving it
 Type is user, app, device, network or other

• Requirements
Mapping can
show graphically
where stuff is,
what kind of
apps are used,
and existing
connectivity

Network analysis and design unite_-i.ppt

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