K. Salah 1

Module 1.1: Introduction (cont.)

• Business Goals and Constraints

• Analyzing Technical Goals

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Understanding the Customer

• A good network design must recognize the customer’s requirements - need to make sure your design meets THEIR needs and not just YOURS!

• The “Customer” may be your own firm, the “who” you are designing the network for

• Need an overview of a customer’s requirements

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Business Goals

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• Scalability

• Availability

• Network Performance– Utilization, Throughput, Accuracy, Efficiency, Delay, and Response

Time

• Security

• Manageability

• Usability

• Adaptability

• Affordability

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Scalability

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

Token Ring w LLC

Ethernet w LLC

802.2 – Logical Link Control header used with Ethernet and Token Ring

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Efficiency and Routing Protocol Overheads

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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 $