Connecting Through a Cabled Network

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• Chapter 4
• Connecting Through a Cabled Network

BUSI-138, ESB, UOP
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Communications Media Types

• OSI Layer 1 communication media and interfaces
• Five basic communication media types
• Coaxial cable based on copper wire
• Twisted-pair cable based on copper wire
• Fiber-optic cable glass or plastic cable
• Hybrid fiber/coax combines copper and fiber
• Wireless technologies radio or microwaves
• Suitability of media varies with different
  networks
• Example uses of coaxial cable
• Older LANs
• LANs in areas with signal interference strong
• Connecting wireless antenna to network device

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Communications Media Types (continued)

• Consider capabilities and limitations of media
• Factors affecting choice of LAN or WAN medium
• Data transfer speed
• Use in specific network topologies
• Distance requirements
• Cable and cable component costs
• Additional network equipment that might be
  required
• Flexibility and ease of installation
• Immunity to interference from outside sources
• Upgrade options
• Security

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Coaxial Cable

• Two types of coaxial cable (coax)
• Thick used in early networks, typically as
  backbone
• Backbone cabling between network equipment
  rooms, floors, and buildings
• Thin used to connect desktops to LANs
• Has much smaller diameter than thick coax
• Use of both thick and thin coaxial cables
  declining

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Thick Coax Cable

• Thick coax cable (thickwire, thicknet, RG-8)
• Has relatively large .4-inch diameter
• Copper or copper-clad aluminum conductor at core
• Conductor surrounded by insulation
• Aluminum sleeve wrapped around insulation
• PVC or Teflon jacket covers aluminum sleeve
• Connect device at minimum of 2.5 m of cable length

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Thick Coax Cable (continued)

• Two transmission types
• Baseband one node controls entire channel
  capacity
• Broadband multiple nodes on multiple channels
• Bandwidth capacity of a channel to transmit
• 10Base5 IEEE spec for maximum segment length
• 10 indicates transmission rate of 10 Mbps
• 5 indicates 500 meters for longest cable run
• Conditions for optimal performance of thick coax
• Carrying data on bus networks
• Using baseband transmission up to 10 Mbps

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Thin Coax Cable

• Ethernet specifications for thin coax cable
• 50 ohms of impedance (RG-58A/U or Radio Grade 58)
• Meets criteria in 10Base2 designation
• Maximum theoretical speed of 10Mbps
• Wire runs up to 185 meters (formerly 200)
• Used for baseband (Base) data transmission
• Thin coax like thick coax with smaller diameter
  (.2")
• Implementing thin coax cable
• Attached to bayonet connector (BNC)
• BNC connected to T-connector
• Middle of T-connector attached to NIC
• Terminator may be attached to one end of
  T-connector

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Thin Coax Cable (continued)

• Advantages of thin coax cable
• Easier and cheaper to install than thick coax
• More resistant to EMI and RFI (interferences)
  than twisted pair

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Twisted Pair Cable

• Twisted-pair cable
• Contains pairs of insulated copper wires
• Outer insulating jacket covers wires
• Communication specific properties
• Copper wires twisted to reduce EMI and RFI
• Length up to 100 meters
• Transmission speed up to 10 Gbps
• RJ-45 plug-in connector attaches cable to device
• Less expensive and more flexible than
  T-connectors
• Two kinds of twisted pair cable shielded and
  unshielded (preferred)

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Shielded Twisted Pair Cable

• Shielded Twisted Pair Cable (STP)
• Surrounded by braided or corrugated shielding
• Shielding reduces interference due to EMI and RFI
• Further reducing impact of EMI and RFI
• Interval of twists (lay length) in each pair
  should differ
• Connectors and wall outlets should be shielded
• Have proper grounding
• Shielded cable and associated equipment expensive

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Unshielded Twisted-Pair Cable

• Unshielded Twisted-Pair Cable (UTP)
• Consists of wire pairs within insulated outer
  covering
• Has no shielding between wires and encasement
• UTP is most frequently used network cable
• Reducing EMI and RFI
• Twist interior strands (like STP)
• Build media filter into network equipment,
  workstation, and file connection servers
• UTP cables used in 10BaseT networks
• Category 3 transmission rates up to 16 Mbps
• Category 4 transmission rates up to 20 Mbps

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Unshielded Twisted-Pair Cable (continued)

• Category 5 UTP has 100 Mbps transmission rate
• Category 5e (enhanced) UTP vs. Category 5 UTP
• 1 Gbps transmission rate
• Uses better-quality copper
• Has higher twist ratio for better EMI/RFI
  protection
• Category 6 UTP
• Wire pairs wrapped within insulating foil
• Has fire resistant plastic sheath
• 1 Gbps transmission rate
• Category 7 UTP enhances protective foiling

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Unshielded Twisted-Pair Cable (continued)

• Reasons for preferring UTP over STP
• Fewer points of failure
• Has no shield that can tear (up through Category
  5e)
• Connectors and wall outlets do not need shielding
• Proper grounding not as critical to purity of
  signal
• Horizontal cabling (defined by EIA/TIA-568
  standard)
• Cabling connecting workstations/servers in work
  area
• Implemented with Categories 5e, 6, and 6e UTPs
• Categories facilitate future equipment upgrades

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Fiber-Optic Cable

• Fiber-optic cable
• One or more glass or plastic fiber cores encased
  in glass tube (cladding)
• Fiber cores and cladding are surrounded by PVC
  cover
• Signal transmissions consist light (usually
  infrared)
• Three commonly used fiber-optic cable sizes
• 50/125 micron
• Micron (µm) millionth of a meter
• 50 represents core diameter
• 125 represents cladding diameter
• 62.5/125 micron
• 100/140 micron

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Fiber-Optic Cable (continued)

• Advantages of fiber-optic cables
• Each cable type has multimode transmission
  capacity
• Transmission speeds from 100 Mbps to over 100
  Gbps
• No EMI or RFI problems, data travels by light
  pulse
• Low attenuation (signal loss during travel)
• Secure from unauthorized taps
• Disadvantages of fiber-optic cables
• Fragile
• Expensive
• Requires specialized training to install
• Cannot be used for analog communications

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Fiber-Optic Cable (continued)

• Uses of fiber-optic cables
• Cable-plant backbones
• Fat pipe high bandwidth backbone between floors
• Connect different buildings in campus environment
• Joining spread-out LANs into a WAN
• Basic characteristics of light transmission
• Infrared light in range of 700 -1600 nanometers
  (nm)
• Three ideal wavelengths (windows) 850 nm, 1300
  nm, 1550 nm

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Fiber-Optic Cable (continued)

• Fiber-optic cable comes in two modes
• Single-mode used for long-distance communication
• 8-10/125 micron cable transmits one wave at a
  time
• Communications signal is laser light
• Multimode supports multiple waves (broadband)
• Comes in two varieties step index and graded
  index
• Cable diameter between 50 and 115 microns
• Source for multimode cable is light-emitting
  diode (LED)

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Hybrid Fiber/Coax Cables

• Hybrid fiber/coax (HFC) cable
• Single sheath containing fibers and copper cables
  
• Different combinations for different
  implementations
• How HFC cables improve cable networks
• Increase upstream bandwidth and reduce noise
• HFC drawbacks expensive and not fully installed
• Services possible using HFC cables
• Plain old telephone service (POTS)
• Up to 37 analog and 188 TV channels
• Up to 464 digital point channels
• High-speed, two-way digital data link for PCs

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High-speed Technologies For Twisted-Pair And
Fiber-Optic Cable

• High-speed threshold 10 Mbps
• Three technologies enhancing cables for
  high-speed
• Fast Ethernet
• Gigabit Ethernet
• 10 Gigabit Ethernet

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Fast Ethernet

• Fast Ethernet 100 Mbps data transfer over
  twisted-pair cable
• Two Fast Ethernet technologies
• 100BaseVG or 100VG-AnyLAN
• 100BaseX

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The IEEE 802.3u Standard

• IEEE 802.3u (100BaseX) Fast Ethernet
• Versions of 100BaseX 100BaseT, 100BaseTX,
  100BaseT4, 100BaseT2, 100BaseFX
• Common properties of standards (except 100BaseT2)
  
• All use CSMA/CD media access methods
• All propagate signal in more than one direction
• Signal transmitted with twisted-pair or
  fiber-optic cable
• Limitations and restrictions
• Segment limitation for twisted-pair same as
  10BaseT
• Use only one Class I repeater or two Class II
  repeaters

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The IEEE 802.12 Standard

• IEEE 802.12 (100BaseVG/100VG-AnyLAN)
• Abandons CSMA/CD for demand priority
• Demand priority
• Ensures signal travels in one direction
• Used in star networks based on central hub
• Grants requests one by one
• Benefits of demand priority
• Enables packet travel up to 100 Mbps
• Security packet visible only to receiving node
• Prioritizes multimedia and time sensitive
  transmissions

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Gigabit Ethernet

• Gigabit Ethernet (1000BaseX)
• Provides data transfer of up to 1 Gbps
• Uses CSMA/CD access methods
• Upgrade path for 100BaseX Ethernet networks
• Uses of Gigabit Ethernet
• Alternative for backbone LAN congestion
• Attract token ring users with star-based
  topologies
• Gigabit Ethernet target
• Installations using Layer 3 routed communications
• Separate standards for fiber-optic and
  twisted-pair cables

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10 Gigabit Ethernet

• IEEE 802.3ae (10 Gigabit Ethernet or 10GBaseX)
• High-speed networking protocol
• Competes with other high-speed MANs and WANs
• Provides fast backbone networking in LANs
• True Ethernet with some differences
• Operates at full duplex (transmission in two
  directions)
• Does not need to employ CSMA/CD
• No packet collisions by design
• How to distinguish various standards
• By interfaces and transmission characteristics

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