Physical Media 1 Physical Media physical link what

Physical Media 1

Physical Media • physical link: what lies between transmitter & receiver • guided media: – signals propagate in solid media: copper, coax, fiber • unguided media: – signals propagate freely, e. g. , radio signals 2

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

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 link layer 4

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

Twisted Pair • Common connectors for Twisted Pair – RJ 11 (6 pairs) – RJ 45 (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) 6

UTP • Unshielded Twisted Pair – Limited amount of protection from interference – Commonly used for voice and Ethernet • Voice: multipair 100 -ohm UTP 7

STP • Shielded Twisted Pair – UTP susceptible to radio and electrical interference – To reduce this interference, extra shielding material added to obtain STP – Cables heavier, bulkier, and more $$ – Often used in token ring topologies • 150 ohm STP two pair (IEEE 802. 5 Token Ring) – Not as common as UTP 8

Coaxial cable • Single copper conductor at center • Plastic insulation layer • Highly resistant to interference – Braided metal shield – Support longer connectivity distances over UTP 9

Coaxial cable • Thick (10 Base 5) – Large diameter 50 -ohm cable – N connectors • Thin (10 Base 2) cables – Small diameter 50 -ohm cable – BNC, RJ-58 connector • Video cable – 75 -ohm cable – BNC, RJ-59 connector – Not compatible with RJ-58 10

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 11

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 12

PL: Fiber connectors • ESCON • Duplex SC • ST • MT-RJ (multimode) • Duplex LC 13

Wireless • Entire spectrum of transmission frequency ranges – – – – Radio Infrared Lasers Cellular telephone Microwave Satellite Acoustic (see ESE sensors) Ultra-wide band • http: //www. ntia. doc. gov/osmhome/allochrt. html 14

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What runs on them? Protocol Summary Protocol Cable Speed Topology Ethernet Twisted Pair, Coaxial, Fiber 10 Mbps Linear Bus, Star, Tree Fast Ethernet Twisted Pair, Fiber 100 Mbps Star Local. Talk Twisted Pair . 23 Mbps Linear Bus or Star Token Ring Twisted Pair 4 Mbps - 16 Mbps Star-Wired Ring FDDI Fiber 100 Mbps Dual ring ATM Twisted Pair, Fiber 155 -2488 Mbps Linear Bus, Star, Tree 16

Summary • When connecting 2 nodes, you have 2 choices: • Use wires to connect the nodes: – What cable to use to connect the transmitter and receiver? • Twisted Pair • Coax • Fiber • Wireless transmission 17