networked computers

					        Data Communications and
        Computer Networks: A
        Business User’s Approach


Chapter 14
Network Design and Management



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Introduction
Properly designing a computer network is a difficult task. It
requires planning and analysis, feasibility studies, capacity
planning, and baseline creation skills.
Performing network management is difficult too. A network
manager must possess computer and people skills, management
skills, financial skills, and be able to keep up with changing
technology.


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Systems Development Life Cycle (SDLC)
Every business has a number of goals.
System planners and management personnel within a company
try to generate a set of questions, or problems, to help the
company achieve those goals.
To properly understand a problem, analyze all possible
solutions, select the best solution, and implement and maintain
the solution, you need to follow a well-defined plan.
SDLC is a methodology, or plan, for a structured approach to
the development of a business system.                             3
Systems Development Life Cycle
SDLC involves several phases. These phases are often:
• Planning
• Analysis
• Design
• Implementation
• Maintenance
These phases are cyclical and usually never ending.




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               Cycle of the phases
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Systems Development Life Cycle
A systems analyst is typically responsible for managing a project
and following the SDLC phases.
Anyone, however, may be called upon to assist a systems
analyst.
Or anyone may have to assume some of the duties of a systems
analyst.
Individuals that are called upon to support a computer network
should understand the basic phases of SDLC.
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Systems Development Life Cycle
Planning Phase - Identify problems, opportunities, and
objectives.
Analysis Phase - Determine information requirements.
Information requirements can be gathered by sampling and
collecting hard data, interviewing, questionnaires, observing
environments, and prototyping.
Design Phase - Design the system that was recommended and
approved at the end of the analysis phase.
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Systems Development Life Cycle
Implementation Phase - The system is installed and preparations
are made to move from the old system to the new.
Maintenance Phase - The longest phase, involves the ongoing
maintenance of the project.
Maintenance may require personnel to return to an earlier phase
to perform an update.


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Network Modeling
When updating or creating a new computer system, the analyst
will create a set of models for both the existing system (if there
is one) and the proposed system.
Network models can either demonstrate the current state of the
network or can model the desired computer network.
A location connectivity diagram is a network modeling tool that
depicts the various locations involved in a a network and the
interconnections between those locations.
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Network Modeling
An overview location connectivity diagram shows the big
picture of geographic locations of network facilities.
External users and mobile users can be identified, as well as the
locations primary to a business.
A detailed location connectivity diagram is a close-up model of
a single location and the networks that reside at the location.
Working groups and the distances between those groups can be
identified with a detailed diagram.                         11
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  X means a special site                      12
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Feasibility Studies
There are a number of ways to determine if a proposed system is
going to be feasible.
Technically feasible means the proposed system can be created
and implemented using currently existing technology.
   It can be done.

Financially feasible means the proposed system can be built
given the company’s current financial ability.
   We can afford it.

Operationally feasible means the system operates as designed
and implemented.
   It’ll work after we build it and it will be used.
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Feasibility Studies
Time feasible means the system can be constructed in an agreed
upon time frame.
Payback analysis ascertains costs and benefits of proposed
system usually on an annual basis.
Payback analysis is a good technique to use to determine
financial feasibility.
To calculate payback analysis, you must know all the expenses
that will be incurred to create and maintain the system, as well
as all possible income derived from the system.
You must also be aware of the time value of money (a dollar
today is worth more than one dollar promised a year from now
because the dollar can be invested).                         15
System Costs:
One time costs:
    Personal costs
    Computer usage costs for analysis
    Hardware and software
    Training, support and management
    Supplies, furniture, space
Recurring costs:
    Lease payments
    Licenses
    Salaries of support personal
    Ongoing supplies
    Maintenance
    Planned replacement
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Note profit
at 6th year




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Capacity Planning
Capacity planning involves trying to determine the amount of
network bandwidth necessary to support an application or a set
of applications.
A number of techniques exist for performing capacity planning,
including linear projection, computer simulation, benchmarking,
and analytical modeling.
Linear projection involves predicting one or more network
capacities based on the current network parameters and
multiplying by some constant.                                19
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Capacity Planning
A computer simulation involves modeling an existing system or
proposed system using a computer-based simulation tool.
Benchmarking involves generating system statistics under a
controlled environment and then comparing those statistics
against known measurements.
Analytical modeling involves the creation of mathematical
equations to calculate various network values.

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Creating a Baseline
Involves the measurement and recording of a network’s state of
operation over a given period of time.
A baseline can be used to determine current network
performance and to help determine future network needs.
Baseline studies should be ongoing projects, and not something
started and stopped every so many years.


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Creating a Baseline
To perform a baseline study, you should:
• Collect information on number and type of system nodes,
including workstations, routers, bridges, switches, hubs, and
servers.
• Create an up-to-date roadmap of all nodes along with model
numbers, serial numbers and any address information such as IP
or Ethernet addresses.
• Collect information on operational protocols used throughout
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the system.
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Creating a Baseline
To perform a baseline study, you should:
• List all network applications, including the number, type and
utilization level.
• Create a fairly extensive list of statistics to help meet your
goals. These statistics can include average network utilization,
peak network utilization, average frame size, peak frame size,
average frames per second, peak frames per second, total
network collisions, network collisions per second, total runts,
total jabbers, total CRC errors, and nodes with highest          23
percentage of utilization.
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Network Manager Skills
A good network manager will possess many skills:
• Computer skills
• People skills
• Management skills
• Financial planning skills
• Knowledge of statistics
• Speaking and writing skills                          25
Generating Useable Statistics
Statistics, properly generated, can be an invaluable aid to
demonstrating current system demands and predicting future
needs.
Mean time between failures (MTBF)
Mean time to repair (MTTR)
Availability is the probability that a particular component or
system will be available during a fixed time period
Reliability is the probability that over a period of time the
particular component or device will be available
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Generating Useable Statistics
Mean time between failures (MTBF) is the average time a device
or system will operate before it fails.
   (from the manufacturer!)
   Large or small?

Mean time to repair (MTTR) is the average time necessary to
repair a failure within the computer system.
   Includes swap time, time to bring the system back up, replacement time,
   etc.
   Large or small?


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Generating Useable Statistics
Availability is the probability that a particular component or
system will be available during a fixed time period.


       A(t) = a/(a+b) + b/(a+b) x e-(a+b)t
       A = 1 means the system is nearly always operational

in which:      a = 1/MTTR
               b = 1/MTBF
               e = natural log function
               t = the time interval


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Generating Useable Statistics
Suppose we want to calculate the availability of a modem that has a
MTBF of 3000 hours and a MTTR of 1 hour. The availability of this
modem for an 8-hour period is:

a = 1/1
b = 1/3000 = 0.00033
A(8 hours) =1/(1 + 0.00033) + 0.00033/(1 + 0.00033) x e-(1 + 0.00033)8
              =       0.9997 + 0.00033 x 0.000335
              =       0.9997

Not available 3 out of 10,000 times you want it.



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Generating Useable Statistics
Reliability is the probability that over a period of time the
particular component or device will be available (not fail):

                       R(t) = e –bt
                       R(0) = e –0 = 1

in which:      b = 1/MTBF
               t = the time interval of the operation
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Generating Useable Statistics
What is the reliability of a modem if the MTBF is 3000 hours
and a transaction takes 20 minutes, or 1/3 of an hour (0.333
hours):

R(0.333 hours) = e -(1/3000)(0.333) = e -0.000111 = 0.99989
Not reliable for .011 percent of the time.

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Generating Useable Statistics
So what do you want?

Availability and reliability between 0.9999 and 0.99999 is
desired!

What is this in number of hours between failure for a year of
service?

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Managing Operations
There are many services and functions available to assist an
individual in managing computer network operations.
One of the more useful is Simple Network Management
Protocol (SNMP).
SNMP is an industry standard designed to manage network
components from a remote location.
Currently in version 3, SNMP supports agents, managers, and
the Management Information Base (MIB).                      33
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Managing Operations
A managed element has management software, called an agent,
running in it.
A second object, the SNMP manager, controls the operations of
a managed element and maintains a database of information
about all managed elements.
A manager can query an agent to return current operating
values, or can instruct an agent to perform a particular action.
The Management Information Base (MIB) is a collection of
information that is organized hierarchically and describes the     34
operating parameters of all managed agents.
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Managing Operations
SNMP operates on a network between the application layer and
the UDP/IP layer (not TCP/IP) – the transport layer.




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Network Diagnostic Tools
To assist a network support person, a number of diagnostic tools
are available:
• Electrical testers (voltage, etc.)
• Cable testers (open circuits, etc.)
• Network testers (view the entire network0
• Protocol analyzers (monitors packets)

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Capacity Planning and Network Design In
Action: BringBring Corporation
Returning to BringBring Corporation from an earlier chapter,
let’s complete our design, including e-mail and Internet access
for each of the four sites.
A linear projection can be used to estimate the amount of
Internet traffic at each site.
An overview location connectivity diagram gives us a big
picture of the network interconnections.
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Capacity Planning and Network Design In
Action: BringBring Corporation
A second linear projection can be used to determine the amount
of local area network traffic within each site.




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