CIS 460 - Network Analysis and Design - PowerPoint PPT Presentation

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CIS 460 - Network Analysis and Design

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Title: CIS 175 - Introduction to Networking Author: David A. Reid Last modified by: Anvari Created Date: 3/27/1999 3:19:24 PM Document presentation format – PowerPoint PPT presentation

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Title: CIS 460 - Network Analysis and Design


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  • The 80/20 rule is no longer valid (80 stays in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

5
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

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 (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

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 (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

10
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

11
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

12
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

13
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

14
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

15
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

16
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

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 (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

22
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.
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