Network Design and Management

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Data Communications and Computer Networks A
Business Users 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.
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• 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.
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X means a special site
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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 companys current
financial ability. We can afford
it. Operationally feasible means the system
operates as designed and implemented. Itll 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).

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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 Plan
ned 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.
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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 networks 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 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
  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

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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/(ab) b/(ab) x e-(ab)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).
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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 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, lets
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.