Wire Media: UTP

• Unshielded Twisted Pair (UTP)

– Ordinary copper wire

– Twisted several times per inch to reduce interference

– Pair of wires needed for a complete electrical signal

– Unshielded: nothing but plastic coating• No protection from interference

Wire Media: UTP• Unshielded Twisted Pair (UTP)

– Business telephone wiring traditionally comes in 4-pair UTP wire bundles

– Used in LAN wiring to use existing building wiring technology

Wire Propagation: RJ-45

• RJ-45 connector terminates a UTP bundle

– Slightly wider than RJ-11 residential connector

– Width needed for 8 wires

Wire Media: UTP to the Desktop• UTP

– Dominant for line from desktop to first hub or switch

– Inexpensive to buy and install

– Rugged: can take punishment of office work

– Easily 100 Mbps, 1 Gbps with careful insulation

UTP

First Hub or Switch

Wire Media: Optical Fiber• Optical Fiber

– Glass core, surrounding glass cladding– Light source turned on/off for 1/0– Total internal reflection at boundary– Almost no attenuation

LightSource

Cladding

Core

Reflection

Wire Media: Optical Fiber• Limited by Distortion

– Light entering at different angles travels different distances (different number of reflections)

– Called different modes

– Light from successive bits becomes mixed over long distances

LightSource

Wire Media: Optical Fiber• Multimode Fiber

– Wide core makes easy to splice (50 or 62 microns)

– Many angles for rays (modes)

– Short propagation distance (usually 200 m to 500 m)

LightSource

Mod B

Wire Media: Optical Fiber• Single Mode Fiber

– Narrow core difficult to splice (5 or 8 microns)

– Only one angle for rays (one mode), so (almost) no distortion

– Longer propagation distance (usually up to 2 km for LAN fiber, longer for long-distance fiber)

– Narrow core makes fiber fragile and difficult to splice

Wire Media: Optical Fiber

• Optical Fiber– High speeds over long distances

• 200 m to 2 km

– Costs more than UTP, but worth it on long runs

– Good for all links between hubs and switches within and between buildings in a site network

OpticalFiber

Wire Media: UTP and Optical Fiber• The emerging pattern: UTP from first hub

or switch to desk, Fiber everywhere else on site

Wire Media: Coax

• Coaxial Cable

– Used in cable TV, VCRs

– Central wire, external concentric cylinder

– Outer conductor wrapped in PVC

Screw-On Connector

InnerWire

Outer Conductor Wrapped in PVC

Wire Media: Coaxial Cable

• Coaxial Cable

– Installed widely today in old 10 Mbps Ethernet LANs

– Not being used in new installations

• Optical fiber more cost-effective for long links

• UTP more cost-effective for desktop links