1. CIS 460 - Network Analysis and Design
Chapter 2
Analyzing Technical Goals and Constraints

2. Analyzing Technical Goals and Constraints
Goals include:
scalability
availability
performance
security
manageability
usability
adaptability
affordability
Tradeoffs associated with these goals
Provides terminology to discuss technical goals with customer

3. Scalability How much growth a network design must support
maybe a prime goal for some
Proposed design should be able to adapt to increase in usage/scope
Planning for Expansion
How many sites to add
How extensive the networks for each new site
How many more users to access the corporate network
How many more servers or hosts to add to the internetwork

4. Scalability (Cont’d) Expanding the Data Available to Users
Empowered employees make strategic decisions that require access to sales, marketing, engineering and financial data
The 80/20 rule is no longer valid (80 % stays in local LANs, 20% destine for other places)
Increasing access to WWW servers
Increasing intranet usage
Strategic alliances with suppliers/customers

5. Scalability (Cont’d)
Technical goals for scaling/upgrading enterprise networks:
Connect separate department LANs in corporate internetworks
Solve LAN/WAN bottleneck problems
Provide centralized servers that reside on server farms
Merge an independent SNA network w/enterprise IP network
Add new sites to support field offices & telecommuters
Add new sites to support communication with customers, suppliers, resellers, and other business partners
Constraints
There are impediments to scalability due to incorrect technology

6. Availability
Refers to the amount of time a network is available to users and is often a critical goal
Can be expressed as a percent uptime per year, month, week, day, or hour
Also lined to reliability but has a more specific meaning (percent uptime) than reliability. Reliability refers to a variety of issues, including accuracy, error rates, stability and TBF.
Also associated with resiliency - how much stress a network can handle and how quickly a network can rebound from problem.
Disaster recovery. Disaster recovery plan

7. Availability (Cont’d)
Specifying Availability Requirements
Specify with precision (% uptime), timeframe(day or night downtime), time unit (day, week, etc.)
Cost of Downtime
For critical applications document how much lost per hour
Also helps to determine whether in-service upgrades must be supported
MTBF/MTR
Define as mean time between failures and mean time to repair
They can be used to calculate availability goals
4000 hours MTBF is a common goal
Good idea to identify for specific applications in addition to network as a whole
Can usually use data supplied by manufacturer for equipment

8. Network Performance Criteria for accepting network performance
throughput, accuracy, efficiency, delay, and response time
Tightly tied to analyzing the existing network to determine what changes need to be made to meet performance goals.
Also tightly linked to scalability goals
Definitions
capacity (bandwidth), utilization, optimum utilization, throughput, offered load, accuracy, efficiency, delay (latency), delay variation, response time

9. Network Performance (Cont’d)
Optimum Network Utilization
measure of how much bandwidth is used during a specific time period. Commonly specified as a percentage of capacity
Various tools 7used to measure usage and averaging the usage over elapsed time.
Customer may have a network design goal for the maximum average network utilization allowed on shared segments.
For shared Ethernet should not exceed 37 percent else collision rate becomes excessive
Toke Ring/FDDI typical goal is 70 percent
For WANs optimum is also about 70 percent

10. Network Performance (Cont’d)
Throughput
the quantity of error -free data that is transmitted per unit of time
Ideally should be the same as capacity, however nout usually
Capacity depends on the physical-layer technologies in use
Depends on the access method
Throughput of Internetworking Devices
Some specify goals as Number of packets per second
The maximum rate the device can forward packets without dropping

11. Network Performance (Cont’d)
Application layer throughput
a measure of good and relevant application-layer data transmitted per unit of time (also called goodput)
Can increase throughput not goodput because extra data transmitted is overhead data
Usually measure in kilobytes or megabytes per second
Constraints
end-to-end error rates
protocol functions such as handshaking, windows, & acknowledgments protocol parameters such as frame size
protocol parameters such as frame size and retransmission timers
PPS or CPS rate of internetworking devices
Lost packets or cells at internetworking devices
Workstation and server performance factors

12. Network Performance (Cont’d)
Accuracy
goal is that data received at the destination must be the same as the data sent by the source. Typical causes include power surges or spikes, failing devices, noise, impedance mismatch, poor physical connection
Accuracy goals can be specified as a bit error rate (BER)
On shared Ethernet errors are often result of collisions
Collision that happens beyond the first 64 bits of a frame is a late collision which are illegal and should never happen
In token rings accuracy goals sometimes include goals for minimizing media-access control error reports

13. Network Performance (Cont’d)
Efficiency
measurement of how effective an 0operation is in comparison to the cost in effort, energy, time, or money
Provides a useful way to talk about network performance
Large frame headers are an obvious cause for inefficiency
Goal is to minimize the amount of bandwidth used by headers
Delay and Delay Variation
Users of interactive applications expect minimal delay in receiving feedback
Multimedia applications require a minimal variation in the amount of delay that packets experience
Telnet protocol applications are also sensitive to delay because of echo feedback

14. Network Performance (Cont’d)
Causes of Delay
delay is relevant to all data transmission technologies, but particularly satellite links and long terrest4rial cables. Also time required to put digital data on a transmission line. Packet switching delay, router delay, queuing delay
Delay Variation
Digital voice and video applications are effected with jitter, or disrupted communications. Can be minimized using a buffer to minimize jitter
Response Time
the network performance goal that users care about most. They recognize small changes in the expected response time. If less than 100 ms most users do not notice

15. Security
Overall goal is that security problems should not disrupt the company’s ability to conduct business.
Have protection so that business data and other resources are not lost or damaged
First task is planning which involves analyzing risks and developing requirements.
Hackers, financial costs, sensitive of customer data

16. Security (Cont’d) Security Requirements
protect resources from being incapacitated, stolen, altered, or harmed.
Let outsiders access data on public web but not internal data
authorize/authenticate branch-office users, mobile users & telecommuters
detect intruders
physically secure hosts and internetworking devices
protect applications and data from viruses
train network users and network managers on security risks

17. Manageability Includes the following network management functions
performance management
fault management
configuration management
security management
accounting management

18. Usability
Refers to the ease-of-use with which network users can access the network and services
some network design components can have a negative effect on usability

19. Adaptability
A good network can adapt to new technologies and changes
New protocols, new business practices, new fiscal goals, new legislation or other possibilities
Effects it availability
A flexible design as enables a network to adapt to changing traffic patterns

20. Affordability Sometimes called cost-effectiveness
Primary goal is to carry the maximum amount of traffic for a given financial cost
In a campus network low cost of often the primary goal
For enterprise networks availability is usually more important than low cost
Minimizing hiring, training, and maintaining personnel to operate and manage the network is also an important goal

21. Affordability (Cont’d)
Making Network Design Tradeoffs
Need to know how important affordability is to other goals
Availability often requires Redundant components which raises costs
To implement affordability might mean availability must suffer
Your customer should identify a single driving network design goal
Sometimes making tradeoffs is more complex than what has been described because goals can differ for various parts of an internetwork

22. Technical Goals Checklist
You should use a technical goals checklist and Table 2-3 to determine if all the client’s technical objectives and concerns are addressed.