Network Design Issues

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Network Design Issues

• Design and Documentation
• Semester 1, Ch. 8

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Content

• Network design and documentation.
• Planning structured cabling.
• Design practices.
• Electricity and grounding.
• Network power supply.

3
General design process

• Develop a Layer 1 LAN topology
• The type of cable (fiber, coaxial, CAT 5 ).
• The physical (wiring) topology.
• Types of Ethernet topologies.
• Hub, repeater, closet, patch panel ...
• Develop a Layer 2 LAN topology
• To add Layer 2 devices to your topology to
  improve its capabilities.
• Develop a Layer 3 LAN topology
• Build scalable inter-networks.
• Link to WANs.

4
Network Design Issues

• Gather information about the organization
• Make a detailed analysis and assessment of the
  current and projected requirements of those
  people who will be using the network.
• Identify the resources and constraints of the
  organization.
• Financial
• Human Resources
• Skill level of users
• Attitudes of users towards technology
• Documentation for cost estimates, budgeting

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Problem-solving matrices
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Documentation needed as you design a network

• engineering journal
• logical topology
• physical topology
• cut sheets
• problem-solving matrices
• labeled outlets
• labeled cable runs
• summary of outlets and cable runs
• summary of devices, MAC addresses, and IP
  addresses

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Wiring Closets (TIA/EIA 568-A)

• Main Distribution Facility (MDF)
• Intermediate Distribution Facility (IDF)
• Horizontal cabling runs must be attached to a
  central point in star topology (the wiring
  closet, where the patch panels, hubs, etc. are
  installed)

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Wiring Closets (TIA/EIA 569)

• Each floor must have at least one (1) wiring
  closet and additional wiring should be provided
  when the floor area exceeds 1000 square meters.

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Wiring Closet Specifications
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Wiring Closet SpecificationEnvironmental
Specification

• Any room, or closet that you choose to serve as a
  wiring closet should adhere to guidelines
  governing such items as the following 
• materials for walls, floors, and ceilings
• temperature and humidity
• locations and types of lighting
• power outlets
• room and equipment access
• cable access and support

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Walls, Floors Ceilings

• Any openings for conduits or sleeved cores must
  be sealed with smoke and flame retardant
  materials
• All cable leaving the room to IDFs, etc. should
  be via a 10.2cm sleeved core or conduit.

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Walls floors and ceilings

• Rooms must not have a dropped, or false, ceiling.
• If MDF POP may be located inside the room. The
  interior wall of the POP site, behind the PBX,
  should be covered from floor to ceiling with 20mm
  plywood, with minimum of 4.6 m of wall space
• Fire-prevention materials should be used during
  construction.
• NO false or dropped ceiling

 20mm A-C plywood that is at least 2.4m high.
30.5 cm

• MDF 100 lb/ft2
• IDF 50 lb/ft2
• If possible, should be Raised tiled floor or some
  other type of finished surface. (to control dust
  and minimize ESD)

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Temperature and Humidity

• Temperature should be maintained at 21C when all
  equipment is in operation
• Humidity should be maintained between 30-50.
• no water or steam pipes running through or above
  the room, with the exception of a sprinkler
  system.
• Failure to maintain these standards could result
  in UTP wiring corrosion.

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Lighting fixtures/power outlets

• If the closet serves as the MDF - minimum of two
  dedicated, non-switched AC duplex electrical
  outlet receptacles, each on separate circuits.
• It should also have at least one duplex power
  outlet positioned every 1.8 m along each wall of
  the room, and should be positioned 150 mm above
  the floor.
• A wall switch, that controls the rooms main
  lighting, should be placed immediately inside the
  door.
• Lighting requirements for a telecommunications
  closet specify a minimum of 500 lx (brightness of
  light equal to 50 foot candles), and that light
  fixtures be mounted a minimum of 2.6 m above the
  floor.
• Fluorescent lighting may be used if installed
  properly but they are not preferred.

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Room and equipment access

• The door of a wiring closet should be at least .9
  m wide, and should swing open out of the room.
• A wiring hub and patch panel may be mounted to a
  wall with a hinged wall bracket, or with a
  distribution rack
• Hinged wall bracket - 48 cm for the panel to
  swing out from the wall.
• Distribution rack - minimum 15.2 cm of wall
  clearance for the equipment, plus another
  30.5-45.5 cm for physical access by workmen and
  repairmen. A 55.9 cm floor plate, used to mount
  the distribution rack, will provide stability,
• If the patch panel, hub and other equipment are
  mounted in a full equipment cabinet, they require
  at least 76.2 cm of clearance in front, in order
  for the door to swing open. Typically, such
  equipment cabinets are 1.8 m high x .74 m wide x
  .66 m deep.

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Cable access and support
Within 15.2 cm of the wall
10.2 cm
Any wall/ceiling openings that provide access for
the conduit, or sleeved core, must be sealed with
smoke and flame-retardant materials that meet all
applicable codes
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Identifying Potential Wiring Closets

• Draw a floor plan of the building to scale, and
  identify all of the devices that will be
  connected to the network. See pg. 290 (MUST DO
  THIS FIRST!)
• Identify secure locations that are close to the
  POP, that can serve as either the sole wiring
  closet, or as the MDF
• If IDFs are required. The POP is where
  telecommunications services, provided by the
  telephone company, connect to the building's
  communication facilities.
• Determining number of wiring closets
• Use your compass to draw circles that represent a
  radius of 50 m. from each of the potential hub
  locations.
• Are there any potential hub locations whose
  catchment areas substantially overlap? If so, you
  could probably eliminate one of the hub
  locations.
• Are there any potential hub locations whose
  catchment areas can contain all of the devices
  that are to be connected to the network? If so,
  then one of them could probably serve as the
  wiring closet for the entire building
• If you will need more than one hub in order to
  provide adequate coverage for all of the devices
  that will be connected to the network, check to
  see if one of them is closer to the POP than the
  other(s)? If so, you will probably want to select
  it to serve as the MDF.

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Wiring closet Floor plan
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Wiring closet Potential Locations
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Wiring Closets

• If there are any potential wiring closet whose
  catchment areas substantially overlap, you could
  probably eliminate one of the wiring closet.
• If there are any potential wiring closet whose
  catchment areas can contain all of the devices
  that are to be connected to the network, then one
  of them could serve as the wiring closet for the
  entire network.

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Wiring closet Practice

• Do any of the circles overlap?
• Can any of the Potential locations be
  eliminated?
• Do any of the circles provide coverage for all of
  the devices that will be connected to the
  network?
• Which of the Potential locations seems to be the
  best?
• Are there any circles where only a few of the
  devices fall outside the catchment area?
• Which Potential location is closest to the POP?
• Based on your findings, list the three best
  possible locations for wiring closets.
• Based on your findings, how many wiring closets
  do you believe will be required for this network?
  
• What are the advantages and disadvantages of each
  of the Potential locations?

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Wiring closet Practice (cont.)
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Backbone cabling consists of the following

• backbone cabling runs
• intermediate and main cross-connects
• mechanical terminations
• patch cords used for backbone-to-backbone
  cross-connections
• vertical networking media between wiring closets
  on different floors
• networking media between the MDF and the POP
• networking media used between buildings in a
  multi-building campus

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Networking Media for Backbone Cabling

• 100 W UTP (four-pair)
• Be careful, copper can act as a conductor and
  provide a path for lightening of used outside of
  the building
• 150 W STP-A (two-pair)
• 62.5/125 µ optical fiber
• Optical fiber is preferred because its made of
  glass which is an insulator, not a conductor
• Single-mode optical fiber

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Locating an MDF in a Multi-Story Building
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Locating an MDF in a Multi-Building Campus
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Backbone TIA/EIA-568-A

• Each IDF can be connected directly to the main
  distribution facility.
• IDF horizontal cross-connect (HCC).
• MDF main cross-connect (MCC).
• 1st IDF interconnected to a 2nd IDF. The 2nd IDF
  is then connected to the MDF.
• 2nd IDF intermediate cross-connect (ICC).
• No more than one ICC can be passed through to
  reach the MCC.

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Horizontal and Backbone Cabling (Type A)
MDF
IDF
3000m
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Horizontal and Backbone Cabling (Type B)
2500m
500m
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Horizontal and Backbone Cabling
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(No Transcript)
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ELECTRICITY AND GROUNDING
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AC vs. DC

• AC
• Alternating Current
• Can present significant problems for a network
• Adds unwanted voltage to desired signals
• Inconsistent voltage flow (rises and falls)
• DC
• Has constant voltage flow

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Electrostatic discharge (ESD)

• Static electricity.
• The most damaging and uncontrollable form of
  electricity.
• ESD must be dealt with in order to protect
  sensitive electronic equipment.
• ESDs can destroy semiconductors and data
• A solution that can help solve problems that
  arise from ESD is good grounding.

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Safety grounding

• Third connector (round) in power socket is called
  the safety ground connection.
• The safety ground wire is connected to any
  exposed metal part of equipments.
• The motherboards and computing circuits in
  computing equipment are electrically connected to
  the chassis, this also connects them to the
  safety grounding wire.

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Purpose of safety grounding

• Prevent such metal parts from becoming energized
  with a hazardous voltage resulting from a wiring
  fault inside the device.
• Be used to dissipate static electricity.
• Whenever an electrical current is passed through
  this path into the ground, it causes protective
  devices such as circuit breakers to activate.

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Safety Ground Connections

• Large buildings frequently require more than one
  earth ground.
• Separate earth grounds for each building are
  required in multi-building campuses.
• When ground wires in separate locations have
  slightly different potential (voltage), to the
  common and hot wires, they can present a serious
  problem.
• This errant potential voltage would have the
  ability to severely damage delicate computer
  memory chips.

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Network devices on separate building
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Dangerous circuit

• Due to the ground wires for the devices in one
  location having a slightly different potential to
  both the common and hotwires than the ground
  wires for the devices in the second location.
• Anyone touching the chassis of a device on the
  network would receive a nasty shock.
• A good way to avoid having current pass through
  the body, and through the heart, is to use the
  one hand rule.

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Avoiding dangerous circuit

• TIA/EIA-568-A specifications for backbone cabling
  permit the use of fiber optic cable, as well as
  UTP cable.
• UTP could provide a path for potentially fatal
  voltages.
• When multiple buildings are to be networked, it
  is highly desirable to use fiber-optic cable as
  the backbone.
• Whenever copper is used for backbone cabling, it
  can provide a pathway for lighting strikes to
  enter a building.

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NETWORK POWER SUPPLY
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Normal mode vs common mode

• Normal mode problems
• exist between the hot and neutral wires
• do not, ordinarily, pose a hazard to you or to
  your computer. usually intercepted by a
  computer's power supply, an uninterruptible power
  supply, or an AC power line filter.
• Common mode problems
• exist between hot or neutral and the ground
  wires,
• can go directly to a computer's chassis without
  an intervening filter.
• do more damage to data signals than normal mode
  problems.
• harder to detect.

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Power problem
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Typical Power Problems

• Surge
• Voltage increase gt 110
• Hubs are especially vulnerable
• Caused by lightening strikes, the power company,
  or equipment that cycles (AC, elevators, etc.)
• Responsible for nearly ALL hardware damage
• Sag/Brownout
• Sag is a brownout that lasts less than 1 second
• Voltage falls below 80
• Account for large portion of power problems

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Typical Power Problems

• Spike
• Overload of voltage
• Lasts between .5 and 100 microseconds
• Power line has been struck with a hit of at least
  240V (100 increase)
• Caused by lightening, power company, equipment
  that cycles (AC, elevators, etc.)
• Oscillations/Noise (Harmonics)
• Caused by an excessively long wiring run where
  the wire acts as an antenna.

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Surge protector pg. 327-328

• To protect the system equipment from surges
  introduced between the building entrance and the
  system equipment, install the inline surge
  protector between those two points and as close
  as possible to the equipment being protected.
• To protect the system equipment from surges
  introduced between the system equipment and the
  work area, install the inline surge protector
  between those two points and as close as possible
  to the equipment being protected.
• To protect the work area equipment that is
  connected to the Local Exchange Carrier (LEC),
  Campus Backbone Cabling or System Equipment. If
  the work area equipment operates over more than
  one-pair, install the inline surge protector as
  close as possible to the equipment being
  protected.

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Surge suppressor

• Prevent surges and spikes from damaging the
  networking device.
• A device called a metal oxide varistor (MOV) is
  most often used as this type of surge suppressor.
  
• Can hold up to 330 V
• Protects the networking devices by redirecting
  excess voltages, that occur during spikes and
  surges, to a ground.
• Has a limited lifetime.
• Would not be the best choice for your network.

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Uninterruptible Power Supply

• An uninterruptible power source is designed to
  handle only short-duration power outages.
• Best handles sags and brownouts
• If a LAN requires uninterrupted power, even
  during power outages that could last several
  hours, then a generator would be needed to
  supplement the backup provided by a UPS.

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UPS Components
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UPS Types