Physical Layer

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Physical Layer
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Acknowledgments for the slides

• Special thanks to the following people who
  created these Networking slides
• Wuchang Feng
• Srini Seshan
• Jim Kurose
• Ion Stoica
• Kang Li

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Physical Layer

• Plethora of physical media
• Fiber, copper, air
• Specifies the characteristics of transmission
  media
• Too many to cover in detail, not the focus of the
  course

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PL Common Cabling

• Copper
• Twisted Pair
• Unshielded (UTP)
• CAT-1, CAT-2, CAT-3, CAT-4, CAT-5, CAT-5e
• Shielded (STP)
• Coaxial Cable
• Fiber
• Single-mode
• Multi-mode

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PL Twisted Pair

• Most common LAN interconnection
• Multiple pairs of twisted wires
• Twisting to eliminate interference
• More twisting Higher bandwidth, cost
• Standards specify twisting, resistance, and
  maximum cable length for use with particular
  data-link layer

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PL Twisted pair

• 5 categories
• Category 1
• Voice only (telephone wire)
• Category 2
• Data to 4Mbs (LocalTalk)
• Category 3
• Data to 10Mbs (Ethernet)
• Category 4
• Data to 20Mbs (16Mbs Token Ring)
• Category 5 (100 MHz)
• Data to 100Mbs (Fast Ethernet)
• Category 5e (350 MHz)
• Data to 1000Mbs (Gigabit Ethernet)

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PL Twisted Pair

• Common connectors for Twisted Pair
• RJ11 (6 pairs)
• RJ45 (8 pairs)
• Allows both data and phone connections
• (1,2) and (3,6) for data, (4,5) for voice
• Crossover cables for NIC-NIC, Hub-Hub connection
  (Data pairs swapped)

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PL UTP

• Unshielded Twisted Pair
• Limited amount of protection from interference
• Commonly used for voice and ethernet
• Voice multipair 100-ohm UTP

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PL STP

• Shielded Twisted Pair
• Not as common at UTP
• UTP susceptible to radio and electrical
  interference
• Extra shielding material added
• Cables heavier, bulkier, and more costly
• Often used in token ring topologies
• 150 ohm STP two pair (IEEE 802.5 Token Ring)

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PL Coaxial cable

• Single copper conductor at center
• Plastic insulation layer
• Highly resistant to interference
• Braided metal shield
• Support longer connectivity distances over UTP

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PL Coaxial cable

• Thick (10Base5)
• Large diameter 50-ohm cable
• N connectors
• Thin (10Base2) cables
• Small diameter 50-ohm cable
• BNC, RJ-58 connector
• Video cable
• 75-ohm cable
• BNC, RJ-59 connector
• Not compatible with RJ-58

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PL Fiber

• Center core made of glass or plastic fiber
• Transmit light versus electronic signals
• Protects from electronic interference, moisture
• Plastic coating to cushion core
• Kevlar fiber for strength
• Teflon or PVC outer insulating jacket

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PL Fiber

• Single-mode fiber
• Smaller diameter (12.5 microns)
• One mode only
• Preserves signal better over longer distances
• Typically used for SONET or SDH
• Lasers used to signal
• More expensive
• Multi-mode fiber
• Larger diameter (62.5 microns)
• Multiple modes
• LEDs used to signal
• WDM and DWDM
• Photodiodes at receivers

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PL Fiber connectors

• ESCON
• Duplex SC
• ST
• MT-RJ (multimode)
• Duplex LC

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PL Wireless

• Entire spectrum of transmission frequency ranges
• Radio
• Infrared
• Lasers
• Cellular telephone
• Microwave
• Satellite
• Acoustic
• Ultra-wide band
• http//www.ntia.doc.gov/osmhome/allochrt.html

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Wireless Equipment

• PCMCIA Cards
• Lucent (best performance but NDAs)
• Intersil Prism 2 (most used chipset)

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Interference Obstructions

• Multi-path (Diversity Antennas)

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PL What runs on them?
Protocol Summary
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PL Bandwidth lingo

• Specifies capacities over physical media
• Electronic
• T1/DS11.54 Mbps
• T3/DS345Mbps
• Optical (OCoptical carrier)
• OC152 Mbps
• OC3/STM1156 Mbps
• OC12622 Mbps
• OC482488 Mbps
• OC19210 Gbps
• OC76840 Gbps