Learning Objectives
Network Design and Management ITT550
Chapter 2: Business & User Requirements
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List the most important business requirements to gather. Explain the difference information providers and decision makers. Describe some of the business costs of a network failure. List three methods of gathering user requirements. Describe ways to derive technical requirements from non-technical user comments.

[Credit to Shapina and Pricislla for their materials.]

Requirements from the Business Perspective
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Business Requirements
These include:
Key Players Major Milestones Funding Levels Types of Business Activity Estimated growth Reliability and Availability Security Web site and Internet connectivity Remote Access

Must understand the nature of the business that will use it. If you design a network for your company it is easier for you to match network requirements with business strategy. If not, you need to conduct interview with management and key personnel.

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Business Requirements: Key Players
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Business Requirements: Major Milestones
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Know who to ask. Identify key players & key groups from organization chart. 2 types of key players: Information sources – explain business strategies, long-term plans, business requirements. Decision makers – approve overall network design or establish funding levels. Normally information sources & decision makers are from the same person. However, it can be from different person.

Key factor - Timing. Time constraint – Completion deadline. Require project plan for tracking project activities, key players & required dates.

Business Requirements: Funding Levels
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Funding Considerations

Major constraint. Management issue. Top management must get involved. Must consider recurring & nonrecurring costs.

Cost Factor Networking Hardware Networking Software UPS RAID Virus Protection Applications Networking Utilities Diagnostic Equipment Telecom Line Charges Personnel Maintenance Training

Nonrecurring Costs √ √ √ √ √ √ √ √ √

Recurring Cost

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Business Requirements: Type of business Activity
Must understand how the network can help users to perform their task. Example: 50 clerical workers using word processors will strain network much less than 50 architects using CAD systems.

Business Requirements: Estimated Growth
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Good network can be expanded as company grows (Scalable). Estimate how much the company plans to grow. Method: Estimate new employees Estimate network traffic Also need to know where the growth is expected.

Business Requirements: Reliability and Availability
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Business Requirements: Security

Need to determine what will happen to the company if the network goes down. For certain company it will be a minor problem. But, for certain company it will cause serious problem such as: Lost productivity. Lost revenue.

Vary from organization to organization. Main objective: Protect customer information or financial records. Some organizations require high security (Government, Financial Institution). Some organizations may have high security requirements for certain types of information, while other information is considered public domain. Network designer should take note security requirements of each type of application & data.

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Business Requirements: Website & Internet Connectivity
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Business Requirements: Remote Access
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Becoming a mainstay of business. Most companies are finding new ways to use Web to enhance and promote their business. Corporate website or Intranet adds another business requirement in network design. Need to understand the details of an organization’s Internet business strategy.

User need to work anywhere and at anytime. Need a secure & reliable remote LAN access. Remote access allows users to work from distant location.

Business Requirements Output: Business Requirements List
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Business Requirements Output: Business Requirements List
Security Web Site and Internet Connectivity Remote Access Key Players Goals or Desires for the Network Encourage management to express their general desires. Tactical versus Strategic Information List specific functions

Most business requirements documents should address the items we have discussed in this lesson:
Key Players Milestones Initial Funding Level Type of Business Activity Estimated Company Growth Reliability and Availability

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User Requirements: The User’s Perspective
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User Requirements: Common Users Concerns

Find out what network services or functions are important to users. Some services need network (Web Server, E-Commerce) but some don’t. Normally users do not state their requirements in technical terms. You have to become “middle man” between user & technical requirements.

Timely delivery of information. Predictable response times. Reliability & availability. Adaptability. Scalability. Security. Affordable

Scalability
Scalability refers to the ability to grow Some technologies are more scalable
Flat network designs, for example, don’t scale well

Availability

Availability can be expressed as a percent uptime per year, month, week, day, or hour, compared to the total time in that period
For example:
24/7 operation Network is up for 165 hours in the 168-hour week Availability is 98.21%

Try to learn
Number of sites to be added What will be needed at each of these sites How many users will be added How many more servers will be added

Different applications may require different levels Some enterprises may want 99.999% or “Five Nines” availability

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Availability Downtime in Minutes
Per Hour Per Day Per Week Per Year
99.999% 99.98% 99.95% 99.90% 99.70% .0006 .012 .03 .06 .18 .01 .29 .72 1.44 4.32 .10 2 5 10 30 5 105 263

99.999% Availability May Require Triple Redundancy
ISP 1 ISP 2 ISP 3

Enterprise

526 1577

Can the customer afford this?

Availability

Network Performance

Availability can also be expressed as a mean time between failure (MTBF) and mean time to repair (MTTR) Availability = MTBF/(MTBF + MTTR)
For example:
The network should not fail more than once every 4,000 hours (166 days) and it should be fixed within one hour 4,000/4,001 = 99.98% availability

Common performance factors include
Bandwidth Throughput Bandwidth utilization Offered load Accuracy Efficiency Delay (latency) and delay variation Response time

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Bandwidth Vs. Throughput
Bandwidth and throughput are not the same thing Bandwidth is the data carrying capacity of a circuit
Usually specified in bits per second

Other Factors that Affect Throughput
The size of packets Inter-frame gaps between packets Packets-per-second ratings of devices that forward packets Client speed (CPU, memory, and HD access speeds) Server speed (CPU, memory, and HD access speeds) Network design Protocols Distance Errors Time of day, etc., etc., etc.

Throughput is the quantity of error free data transmitted per unit of time
Measured in bps, Bps, or packets per second (pps)

Throughput vs. Goodput vs.

Performance (continued)
Efficiency
How much overhead is required to deliver an amount of data? How large can packets be?
Larger better for efficiency (and goodput) But too large means too much data is lost if a packet is damaged How many packets can be sent in one bunch without an acknowledgment?

You need to decide what you mean by throughput Are you referring to bytes per second, regardless of whether the bytes are user data bytes or packet header bytes Or are you concerned with application-layer throughput of user bytes, sometimes called “goodput” In that case, you have to consider that bandwidth is being “wasted” by the headers in every packet

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Delay from the User’s Point of View
Response Time
A function of the application and the equipment the application is running on, not just the network Most users expect to see something on the screen in 100 to 200 milliseconds

Delay from the Engineer’s Point of View
Propagation delay
A signal travels in a cable at about 2/3 the speed of light in a vacuum

Transmission delay (also known as serialization delay)
Time to put digital data onto a transmission line
For example, it takes about 5 ms to output a 1,024 byte packet on a 1.544 Mbps T1 line

Packet-switching delay Queuing delay

Delay: Example
A packet switch has 5 users, each offering packets at a rate of 10 packets per second The average length of the packets is 1,024 bits The packet switch needs to transmit this data over a 56-Kbps WAN circuit
Load = 5 x 10 x 1,024 = 51,200 bps Utilization = 51,200/56,000 = 91.4% Average number of packets in queue =
(0.914)/(1-0.914) = 10.63 packets

Delay Variation
The amount of time average delay varies
Also known as jitter

Voice, video, and audio are intolerant of delay variation So forget everything we said about maximizing packet sizes
There are always tradeoffs Efficiency for high-volume applications versus low and non-varying delay for multimedia

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Security
Focus on requirements first Detailed security planning later (Chapter 8) Identify network assets
Including their value and the expected cost associated with losing them due to a security problem

Network Assets
Hardware Software Applications Data Intellectual property Trade secrets Company’s reputation

Analyze security risks

Security Risks
Hacked network devices
Data can be intercepted, analyzed, altered, or deleted User passwords can be compromised Device configurations can be changed

Manageability

Reconnaissance attacks Denial-of-service attacks

Fault management Configuration management Accounting management Performance management Security management

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Usability

Adaptability

Usability: the ease of use with which network users can access the network and services Networks should make users’ jobs easier Some design decisions will have a negative affect on usability:
Strict security, for example

Avoid incorporating any design elements that would make it hard to implement new technologies in the future Change can come in the form of new protocols, new business practices, new fiscal goals, new legislation A flexible design can adapt to changing traffic patterns and Quality of Service (QoS) requirements

Affordability
A network should carry the maximum amount of traffic possible for a given financial cost Affordability is especially important in campus network designs WANs are expected to cost more, but costs can be reduced with the proper use of technology
Quiet routing protocols, for example

Network Applications Technical Requirements

Name of Cost of Application Downtime

Acceptable MTBF

Acceptable MTTR

Throughput Goal

Delay Must be Delay Less Than: Variation Must be Less Than:

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Summary
Continue to use a systematic, top-down approach Don’t select products until you understand goals for scalability, availability, performance, security, manageability, usability, adaptability, and affordability Tradeoffs are almost always necessary

Review Questions
What are some typical technical goals for organizations today? How do bandwidth and throughput differ? How can one improve network efficiency? What tradeoffs may be necessary in order to improve network efficiency?

Additional info..
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User Requirements

User Requirements (Continue…) Common Users Concerns
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Timeliness and predictability
Describe the ability to access, transfer, or modify information quickly. Transaction-based systems (point-of-sale, banking, airline, & insurance) need predictable response times & timely information retrieval. Users' perception of system speed is very subjective. For some users, 5 minutes for downloading a file is acceptable but some it is not.

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User Requirements (Continue…) Common Users Concerns
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User Requirements (Continue…) Common Users Concerns
Adaptability
Ability of the system to support users' changing needs. Example, user mobility, or network access from multiple locations, Question to ask: How many users work remotely? What type of applications do they use? Do they work over cellular phone links or plug into hotel telephone jacks? Do file transfers involve confidential information?

Reliability & availability
Reliability - system resources are available to users for a very high percentage of the time. Availability - The amount of time that information stored on a computer system or network is accessible . Example, mainframe-based systems may be available 99.95 percent of the time. Reliability also means that the level of service to the user (in terms of system or network performance) is consistent. Question to ask: Is any network downtime acceptable? If so, how much and when? How much of a response delay is too long?

User Requirements (Continue…) Common Users Concerns
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User Requirements (Continue…) Common Users Concerns
Security
Requirement to guarantee the integrity of the information & physical resources. Computer Security - Measures and controls that ensure confidentiality, integrity, and availability of the information processed and stored by a computer. Example: Backup & data restoration Network Security - Protection of networks and their services from unauthorized modification, destruction, or disclosure.

Scalability
The ability to expand the number of users or increase the capabilities of a network without making major changes to the systems or application software. Example, a user complaints that the network has really been slow since the last software upgrade. Question to ask: Peak traffic times Hiring patterns, Physical network expansion.

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User Requirements (Continue…) Common Users Concerns
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User Requirements (Continue…) Output: User Services Matrix
One method of gathering & documenting user requirements. Provide guideline for discussions with management & users of the network.

Affordable Whether user can afford it or not.

User Requirements (Continue…) Output: User Services Matrix
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ITT550 - Network Design & Management

ITT550 - Network Design & Management

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