CE521042 Network Computer Systems

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CE52104-2Network Computer Systems

• Network Cable Standards

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Overview

• What are/is media?
• What categories or types of media exist?
• What happens to signals sent?
• What are the common media technologies?
• How do they compare?
• Costs
• Performance including speed
• Reliability and fitness for purpose
• Scalability

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Media is a layer 1 device
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Physical Layer Signaling and Encoding

• Terminology
• Bandwidth
• Throughput
• Goodput

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Basic Physics

• Electrons are negatively charged
• Neutrons are neutral
• Protons are positively charged

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Alternating Current - ac

• We refer to circuits as being of one of two types
• The first type is an AC (alternating current)
  circuit
• This refers to the current flow alternating about
  a zero point
• It is of a constantly changing value
• Normally represented as a sinusoidal waveform (a)

• A Amplitude
• T Period (time to complete one cycle)
• f frequency 1/T normally expressed in Hertz,
  where T is measured in seconds

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Direct Current - dc

• The second ciruit type being DC (direct current)
• It is of a constant value
• Normally dc has one or two values
• Typically a logic 1 5V
• Typically a logic 0 0V or Gnd.

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Signalling on the medium
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Signalling on different media
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Problems with dc

• DC signal grow weaker the further they travel
  attenuation.
• Higher frequency attenuate faster
• Male v Female voice
• Signals travel at differing speeds leading to
  different arrival times
• 100 metre race
• Susceptible to noise induced signals
• This can be from large motors,
• fluorescent lighting,
• 3-phase power cables
• Other cables close by carrying signals
  crosstalk
• Not all bad phones connected

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Media types

• Common media include copper cables, optical
  fibres and the air
• Guided media
• twisted pair (UTP/STP),
• coaxial cable (coax),
• optical fibre
• Unguided media
• radio,
• infrared,
• microwave
• Point to point, where two devices share the
  medium
• Multipoint or broadcast where more than two
  devices share the medium

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Twisted pair (UTP STP)

• Insulated copper wires twisted together
• Wires acts as a single communication link
• Often used in telephone networks
• Usually used within buildings
• Comparatively cheap and easy to work with
• Twists help to avoid cross-talk noise effects
• Connected by RJ45 connections
• Two Types
• UTP Unshielded Twisted Pair
• Cheapest media for networks
• STP Shielded Twisted Pair
• More expensive
• Harder to work with

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UTP Cable
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STP Cable
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Cable Categories

• EIA-568-A standard defines these-
• Cat-1 was for telephones and ISDN
• Cat-2 was used by IBM for 4Mbps Token-Ring
• Category 3 UTP capable of 16MHz
• usually run at 10Mbps
• Only good for cable segments to workstations or
  printers.
• Category 4 UTP capable of 20 MHz
• Category 5 UTP capable of 100MHz
• usually run at 100Mbps
• Cat-5e is used for 100Mbps Fast Ethernet and ATM
  at 155Mbps
• Cat-6 is for high speed networks using
  200MHz-250MHz signalling
• Good as a backbone or for general use.

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Classes of balanced cabling

• Class A specified up to 100kHz
• Class B specified up to 1MHz
• Class C specified up to 16MHz
• Class D specified up to 100MHz
• Class E specified up to 250MHz
• Class F specified up to 600MHz

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Coaxial cable

• Single copper wire surrounded by shielding
• Better frequency characteristics,
• higher data rates,
• more immune to interference than twisted pair
• Uses for
• Television distribution,
• Long distance telephone transmission,
• Short run computer I/O channels,
• LANs

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Coaxial Cable
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Fiber Optic Cabling

• Data rates of 2Gbps or more
• Single runs over tens of kilometres
• Low attenuation
• Not susceptible to electromagnetic interference
  or cross-talk
• Used for long haul, metropolitan and rural trunk
  lines, LANs
• See IEEE 802.8 standards for more

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Fiber Optic Cabling
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Fiber Optic Cabling
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Cabling - Range and Speed
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Non Cable Media

• Satellite Microwave provides
• point to point or
• point to multi-point connectivity
• Common for
• TV broadcasting
• Long distance telephone transmission
• Public and private business networks

• Radio
• Omnidirectional broadcasts all around
• Simple antenna, not like satellite microwave
• Antenna alignment allowed to be imprecise
• Good for data networks where some or all stations
  may be mobile

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Summary