CIS 460 - Network Analysis and Design

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CIS 460 - Network Analysis and Design

• Chapter 2
• Analyzing Technical Goals and Constraints

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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

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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

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Scalability (Contd)

• 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• The 80/20 rule is no longer valid (80 stays in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

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Scalability (Contd)

• 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

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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

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Availability (Contd)

• 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

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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

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Network Performance (Contd)

• 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

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Network Performance (Contd)

• 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

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Network Performance (Contd)

• 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

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Network Performance (Contd)

• 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

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Network Performance (Contd)

• 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

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Network Performance (Contd)

• 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

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Security

• Overall goal is that security problems should not
  disrupt the companys 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

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Security (Contd)

• 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

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Manageability

• Includes the following network management
  functions
• performance management
• fault management
• configuration management
• security management
• accounting management

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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

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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

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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

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Affordability (Contd)

• 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

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Technical Goals Checklist

• You should use a technical goals checklist and
  Table 2-3 to determine if all the clients
  technical objectives and concerns are addressed.