Transcript module_1.1 - Faculty Personal Homepage

Module 1.1: Introduction (cont.)
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Business Goals and Constraints
Analyzing Technical Goals
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Understanding the Customer
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A good network design must recognize the customer’s
requirements - need to make sure your design meets THEIR
needs and not just YOURS!
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The “Customer” may be your own firm, the “who” you are
designing the network for
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Need an overview of a customer’s requirements
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Business Goals
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Before we look at the technical details, we first start at the
business goals
Start with researching your client’s business
– what industry are they in
– their market
– their suppliers
– their products
– their services
– the competition they face
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Business Goals - Continued
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Need to understand the organizational structure of the client
– their separate departments
– lines of business
– vendors
– partners
– remote offices
This will help characterize traffic flow and determine user
communities
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Business Goals - Continued
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When you understand the corporate structure, you also identify
who the key decision makers are, who will have final say on your
design proposal when you are finished
You want to understand what are the overall goal of the network
design project
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Questions to Ask
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Why are they doing the network design analysis?
What will the network be used for?
How does the customer think the new network will improve their
business practices?
What is the criteria to be used to judge the network?
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Success Criteria
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What makes the network design a success?
– May be defined differently by the different “stakeholders”
– company executives
– managers
– end users
– network administrators
– system programmers
– any other person or group who has a stake in the network
design project
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Failure Consequences
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What happens if the project does not meet the design objectives?
How visible is the project to upper management?
To what extent could unforeseen behavior of the new network
disrupt business operations?
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The Internet Impact
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The growth of the Internet has made interconnection with it
almost a business priority for network design
Vast amounts of information is now being shared within the
organization using the internet as a design example, normally
called Intranets.
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Typical Business Goals
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Increase revenue and profit
Improve corporate communications
Shorten product development cycles
Build partnerships with other companies
Expand into other markets
Modernize out-dated technologies
Reduce network costs
Make more data available to more people
Improve network security and reliability
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Business Constraints
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Politics and Policies
– Are there people who would like to see you fail?
– What are the companies policy on suppliers
Budget and Staffing Constraints
– Your design must fit the budget
– Staff abilities may determine some of your design
Scheduling
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Analyzing Technical Goals
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Analyzing Technical Goals
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Now that we have discussed Business Goals, lets examine the
Technical Goals that we need to understand and should reflect in
the design of a network
You need to match your network design to fit the customers
technical needs
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Technical Goals & Constraints
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Scalability
Availability
Network Performance
– Utilization, Throughput, Accuracy, Efficiency, Delay, and Response
Time
Security
Manageability
Usability
Adaptability
Affordability
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Scalability
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Scalability - how much growth a network design must support
Need to examine the network needs out a few years - 3 years as a
minimum
Key points to understand
– How many more sites will be added?
– How extensive will the networks be at each site?
– How many more users will be added?
– How many more servers will be added?
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Availability
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Availability is the amount of time a network is available to users
Can be expressed as percent uptime
– 165 hours in 168 hours/week = 98.21%
Redundancy is used to increase a networks availability
Availability is also tied to disaster recovery
99.70 - 30 minutes outage every week
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Network Performance
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There are several measures to look at
– Utilization
– Throughput
– Accuracy
– Efficiency – A key measure
 Protocol Frame Size, Protocol Overhead, and Routing
Protocol Overhead
– Delay
– Response Time
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Network Performance - Utilization
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Is the percent of total available capacity (bandwidth) in use
Bandwidth is measured over a time interval to determine the
amount in use
There are several numbers used to describe when your network
shows delays that impact the usability of the network - will will
examine these later.
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Network Performance - Throughput
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Throughput is defined as the quantity of error-free data
successfully transferred between nodes per unit of time
Depends on network access method, the load on the network
and the error rate
Throughput can be expressed in Packets per Second (PPS) than
can be sent by a device with dropping any packets
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Network Performance -Accuracy
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Accuracy is a measure to ensure that the data received at the
destination must be the same as the data sent by the source
Data errors are caused by power surges, or spikes, poor physical
connections, failing devices and electrical noise
Accuracy can be expressed in Bit Error Rate (BER), typically 1 in
105
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Network Performance -Efficiency
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We measure how effective an operation is
How much “overhead” is needed to send traffic across the
network - the traffic has our data in it
Overhead is due to several factors lets look at some of them:
– Network Protocol Frame Size
– Network Protocol Overhead
– Routing Protocol Overheads
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Efficiency and
Network Protocol Frame Sizes
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Since application data is sent over frames and each frame can
hold some data. Key is how many frames do I need to sent my
data? (each frame has some overhead in it)
– Novell IPX 1,500 byte Frame Size
– Telnet is only 60 bytes
– HTTP (Web) is 1,500 bytes
– Token Ring uses 4,096 bytes
– ATM used 53 byte cells
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Efficiency and
Network Protocol Frame Sizes
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Efficiency and
Network Protocol Overhead
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Remember data is packaged in protocol frames that contain
overhead data, some have more overhead than others
– Ethernet - 38 bytes per frame
– IP - 20 bytes per frame
– TCP - 20 bytes per frame
– IPX - 30 bytes per frame
– ATM - 5 bytes per cell
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Efficiency and
Network Protocol Overhead
802.2 –
Logical Link
Control
header used
with Ethernet
and Token
Ring
Ethernet w LLC
Token Ring w LLC
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Efficiency and
Routing Protocol Overheads
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Remember each routing protocol also use up network bandwidth
– IP RIP - every 30 seconds sends 532 byte packages
– IP IGRP - every 90 seconds sends 1,488 byte packages
– IPX SAP - every 60 seconds sends a 480 byte package
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Efficiency and
Routing Protocol Overheads
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Network Performance -Efficiency Summary
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You want to use a protocol that has a large frame size, and one
that also needs only small header information in each frame
You want an efficient Routing Protocol
This allows us to transfer more data at a higher efficiency across
our network!
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Network Performance - Delay
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Interactive applications demand minimal delay when receiving a
data stream
Delay must be constant for voice and video applications other
wise you will get jitter causing disruptions in voice quality and
jumpiness in video streams
Delay can be caused by physics, and by network devices that
move the data within a network (use buffers to minimize effect)
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Network Performance - Queuing Delay
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Queuing delay is the number of packets in a queue on a packet
switching device
As utilization increases, more packets must wait in the queue
before being put on the wire
Queue depth = utilization/(1-utilization)
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Network Performance - Response Time
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Response time is a network performance goal that users care
about most
Users recognize the amount of time to receive a response from
the network system
Users begin to get frustrated when response time is 100ms (.1
seconds) or so
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Security
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Security design is getting to be one of the most important aspects
of network design
Network design must ensure against loss of business data or
disruption of business activity
Need to understand the risk of data loss
Need to understand ways to get to the data
Need to understand who wants the data
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Manageability
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There are different ways to manage a network and the different
things to manage
– Performance management
– Fault management
– Configuration management
– Security management
– Accounting management
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Usability
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Usability refers to the ease-of-use with which network users can
access the network and services
Focus is on making the network users’ job easier
example is using host naming servers and easy to use
configuration devices such as a DHCP server
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Adaptability
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You want to ensure the network can implement new technologies
in the future
You want it to be able to adapt and change with technology
A flexible network can also adapt to changing network patterns
and quality of service (QoS) requirements
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Affordability
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Affordability is sometimes called cost-effectiveness
Want to carry the maximum amount of traffic for a given financial
cost
Financial costs include non-recurring equipment costs and
recurring network operating costs
WAN costs are an area where a good design can save $
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