Lesson 02 - This lesson explores design issues related to overall network topology. The following sections discuss the traditional issues of bandwidth, delay, and reliability; as well as the often overlooked issues of operational simplicity and scalability, particularly as they pertain to routing.

1. Lesson 02
Network Design and Management
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2. Systems Development Life Cycle
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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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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5. 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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6. 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.
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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7. 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 series of connectivity maps are network modeling tools that depict the
various locations involved over a wide and local areas and the
interconnections between those locations.
An wide area connectivity map 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.
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8. Network Modeling
To identify each connection between sites:
d = distance of the connection (usually shown in either miles or kilometers)
s = security level (high, medium, low, or none)
du = duplexity (full duplex, half duplex, or simplex)
dr = data rate desired (in bps)
l = latency, or acceptable delay time across the network (usually in milliseconds, or
ms)
QoS = Quality of Service (CBR - constant bit rate, VBR - variable bit rate, ABR -
available bit rate, UBR - unreliable bit rate, or none)
de = delivery rate (sometimes called throughput percentage)
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10. Connection from L.A. to Chicago might be:
d = 2250
s = medium
du = full
dr = 256 Kbps
l = 200 ms
QoS = ABR
de = 99.9%
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12. Network Modeling
An metropolitan area connectivity map shows the design of a
metropolitan area and its network facilities.
QoS = VBR
dr = 100 Mpbs
s = high
d = 5 km
failover = 50 ms
de = 99.9%
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14. Network Modeling
An local area overview connectivity map shows the design of a
big picture design of a local area network.
QoS = none
dr = 100 Mpbs
s = none
d = 85 m
du = full
thru = 50%
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16. Network Modeling
An local area detailed connectivity map shows the close-up
design of a local area network, including switches, routers,
hubs, and servers.
Much like the homework we did earlier showing LAN
connections.
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18. 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.
Financially feasible means the proposed system can be built given the company’s
current financial ability.
Operationally feasible means the system operates as designed and implemented.
Time feasible means the system can be constructed in an agreed upon time frame.
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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21. 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.
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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22. 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. 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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23. 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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25. 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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26. 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) is the average time a
device or system will operate before it fails.
Mean time to repair (MTTR) is the average time necessary to
repair a failure within the computer system.
Availability is the probability that a particular component or
system will be available during a fixed time period.
Availability % = (Total available time – Downtime) / Total
available time
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27. Generating Useable Statistics
Suppose we want to calculate the availability of a modem that for
one month (24 hours per day for 30 days, or 720 hours), knowing
the modem will be down for two hours during that period:
Availability % = (720 – 2) / 720
= 0.997
Reliability is defined by the equation:
R(t) = e -bt
in which: b = 1/MTBF
t = the time interval of the operation
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28. 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
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29. 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).
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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30. Network Diagnostic Tools
To assist a network support person, a number of diagnostic tools
are available:
• Electrical testers
• Cable testers
• Network testers
• Protocol analyzers
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31. Capacity Planning and Network Design In
Action: Sample Corporation
Sample Corporation complete 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 wide area connectivity map gives us a big picture of the
network interconnections.
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33. Capacity Planning and Network Design In
Action: Sample Corporation
A second linear projection can be used to determine the amount
of local area network traffic within each site.
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35. Lesson 02
Local Area Networks
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36. Why Interconnect?
To separate / connect one corporate division with another.
To connect two LANs with different protocols.
To connect a LAN to the Internet.
To break a LAN into segments to relieve traffic congestion.
To provide a security wall between two different types of users.
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37. Hubs
As seen earlier, a hub interconnects two or more workstations
into a local area network.
When a workstation transmits to a hub, the hub immediately
resends the data frame out all connecting links.
A hub can be managed or unmanaged. A managed hub
possesses enough processing power that it can be managed from
a remote location.
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38. Bridges
A bridge (or bridge-like device) can be used to connect two
similar LANs, such as two CSMA/CD LANs.
A bridge can also be used to connect two closely similar LANs,
such as a CSMA/CD LAN and a token ring LAN.
The bridge examines the destination address in a frame and
either forwards this frame onto the next LAN or does not.
The bridge examines the source address in a frame and places
this address in a routing table, to be used for future routing
decisions.
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40. Transparent Bridges
A transparent bridge does not need programming but observes
all traffic and builds routing tables from this observation.
This observation is called backward learning.
Each bridge has two connections (ports) and there is a routing
table associated with each port.
A bridge observes each frame that arrives at a port, extracts the
source address from the frame, and places that address in the
port’s routing table.
A transparent bridge is found with CSMA/CD LANs.
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43. Transparent Bridges
A transparent bridge can also convert one frame format to
another, but this does not happen too often anymore since most
networks are CSMA/CD.
Note that some people / manufacturers call a bridge such as this
a gateway or sometimes a router.
The bridge removes the headers and trailers from one frame
format and inserts (encapsulates) the headers and trailers for the
second frame format.
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44. Remote Bridges
A remote bridge is capable of passing a data frame from one
local area network to another when the two LANs are separated
by a long distance and there is a wide area network connecting
the two LANs.
A remote bridge takes the frame before it leaves the first LAN
and encapsulates the WAN headers and trailers.
When the packet arrives at the destination remote bridge, that
bridge removes the WAN headers and trailers leaving the
original frame.
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46. Spanning Tree Algorithm
What happens if you have many LANs interconnected with
multiple bridges, such as shown in the next slide?
Data that leaves one workstation could travel to a bridge, across
the next network, into the next bridge, and back onto the first
network.
A packet may continue to cycle like this forever!
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49. Spanning Tree Algorithm
How do we stop this from happening?
Disconnect one of the bridges? Maybe we want bridge
redundancy in case one bridge fails.
How about applying the spanning tree algorithm.
How is the algorithm applied?
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50. Spanning Tree Algorithm
Step 1: Designate a Root Bridge
Step 2: Mark one port of each bridge as the Root Port. The root port is the
port with the least-cost path from that bridge to the root bridge. The root ports
are denoted with an asterisk.
Step 3: The next step is to select a designated bridge for each LAN. A
designated bridge has the least-cost path between that LAN and the root
bridge. Mark the corresponding port that connects that LAN to its designated
bridge with two asterisks.
Step 4: If a port has no asterisks, that port is redundant and can be “removed”.
Keep all ports with one or two asterisks. The resulting configuration is shown
in Figure 8-7c.
Note there is now only one way to get to any LAN or bridge from any other
LAN or bridge.
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52. Switches
A switch is a combination of a hub and a bridge.
It can interconnect two or more workstations, but like a bridge, it observes traffic flow
and learns.
When a frame arrives at a switch, the switch examines the destination address and
forwards the frame out the one necessary connection.
Workstations that connect to a hub are on a shared segment.
Workstations that connect to a switch are on a switched segment.
The backplane of a switch is fast enough to support multiple data transfers at one time.
A switch that employs cut-through architecture is passing on the frame before the
entire frame has arrived at the switch.
Multiple workstations connected to a switch use dedicated segments. This is a very
efficient way to isolate heavy users from the network.
A switch can allow simultaneous access to multiple servers, or multiple simultaneous
connections to a single server.
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55. Virtual LANs
A virtual LAN, or VLAN, is a logical subgroup within a local area network
that is created via switches and software rather than by manually moving
wiring from one network device to another
Even though the employees and their actual computer workstations may be
scattered throughout the building, LAN switches and VLAN software can be
used to create a “network within a network.”
A relatively new standard, IEEE 802.1Q, was designed to allow multiple
devices to intercommunicate and work together to create a virtual LAN
Instead of sending a technician to a wiring closet to move a workstation cable
from one switch to another, an 802.1Q-compliant switch can be remotely
configured by a network administrator
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56. Isolating Traffic Patterns with Switches
Whether shared or dedicated segments are involved, the primary
goal of a switch is to isolate a particular pattern of traffic from
other patterns of traffic or from the remainder of the network
Switches, because of their backplane, can also allow multiple
paths of communications to simultaneously occur
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59. Isolating Traffic Patterns with Switches
Using a pair of routers, it is possible to interconnect to switched
segments, essentially creating one large local area network
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61. Full Duplex Switches
A full duplex switch allows for simultaneous transmission and
reception of data to and from a workstation.
This full duplex connection helps to eliminate collisions.
To support a full duplex connection to a switch, at least two pairs
of wires are necessary - one for the receive operation and one for
the transmit operation. Most people install four pairs today, so
wiring is not the problem.
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63. Network Servers
Network servers provide the storage necessary for LAN
software.
They are usually the focal point for the network operating
system.
Increasingly, network servers are functioning as bridges,
switches, and routers. By adding the appropriate card, a server
can assume multiple functions.
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64. Routers
The device that connects a LAN to a WAN or a WAN to a WAN.
A router accepts an outgoing packet, removes any LAN headers and trailers, and
encapsulates the necessary WAN headers and trailers.
Because a router has to make wide area network routing decisions, the router has to
dig down into the network layer of the packet to retrieve the network destination
address.
Thus, routers are often called “layer 3 devices”. They operate at the third layer, or OSI
network layer, of the packet.
Routers often incorporate firewall functions.
An example of a router’s operation is shown on the next slide.
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66. A Small Office Sample
A small office with 20 workstations in one room and 15
workstations in another room were connected to a server via
100BaseTX.
One hub was kept in a closet near the 20 workstations while a
second hub was near the server.
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67. Small Office Solution Sample
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68. A Small Office Sample
Now the owner wants to connect the LAN to the Internet.
He adds a router next to the server and connects it to the hub.
He connects the router to a high-speed telephone line such as a
T-1 service.
He will also have to program the router to perform IP addressing
and firewall functions.
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69. Small Office Solution Sample
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70. A Small Office Sample
Now network usage is so high that he must consider segmenting
the network.
He decides to install a database server near the original server
and replace both hubs with switches.
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71. Small Office Solution Sample
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