2 Located below the physical layer Controlled by the physical layer Figure Transmission medium and physical layerTransmission medium(channel): the physical path between the transmitter and the receiver.Located below the physical layerControlled by the physical layer
5 A wire pair acts as a single communication link Figure Twisted-pair cableA twisted pair consists of: two insulated copper wires in a regular spiral patternA wire pair acts as a single communication linkTwisted to reduce electrical interference from similar pairs close by (more twists means better quality)Used in:Telephone network Between house and local exchange (subscriber loop)LAN
6 Twist length of 7.5 cm to 10 cmTwist length 0.6 cm to 0.85 cm
9 Unshielded Twisted Pair (UTP) Used for telephone wireCheapest type of cableEasiest type to be installedSuffers from external Electromagnetic (EM) interferenceShielded Twisted Pair (STP)Metal braid or covering that reduces interferenceMore expensiveHarder to handle (thick, heavy)
10 Table 7.1 Categories of unshielded twisted-pair cables
13 The RJ-45 Connector TD+ : Transmit Data Positive value White/OrangeOrangeWhite/GreenGreenBrown23The RJ-45 Connector18TD+ : Transmit Data Positive valueTD- : Transmit Data Negative valueRD+ : Receive Data Positive valueRD- : Receive Data Negative value
14 TD+ : Transmit Data Positive value TD- : Transmit Data Negative value RD+ : Receive Data Positive valueRD- : Receive Data Negative valueWhite/OrangeOrangeWhite/GreenGreenBrown
15 Ethernet Cabling Crossover Cabling Straight-Through Cabling PC to PC Hub to HubSwitch to SwitchHub to SwitchRouter to PCPC to Switch/HubRouter to Switch/Hub
20 Optical Fiber consists of three concentric sections glass or plastic coverplastic jacketFiber core and cladingCore: consists of one or more very thin strands or fibers made of glass or plasticEach fiber is surrounded by its own cladding, a glass or plastic coating that has optical properties different from the coreJacket: a plastic or other material acts as a layer to protect against moisture, crushing, and other environmental dangers.
21 Fiber Optic CableA fiber optic cable consists of two strands. Each strand has a glass or plastic core surrounded by more glass called cladding. The center strand provides the wave path while the cladding is composed of reflective glass that refracts light back to the core. Each strand is covered in a jacket composed of a group of Kevlar fibers for strength, and a reinforcing layer of plastic..Since, each glass strand only passes signals in one direction, a cable has two strands in separate jackets. Special connectors make up an optically pure connection to the glass fiber and provide a window for laser transmitters and optical receivers.Fiber optic cable is not impacted by outside electric currents because the signals it carries are pulses of light conducted over threads of glass. Because they are free from interference and the light pulses travel for miles without losing appreciable strength, fiber optic cables can carry data at high signaling speeds over long distances. Speeds easily exceed 100 Mbps and distances range approximately 2 Km.Two Types of Fiber Cable follow:Single-Allows only one mode of light to propagate through the fiber, capable of higher bandwidth and greater distances than multimode. Often used for campus backbones. Uses lasers as the light generating method. About the diameter of human hair (8 microns thick).Multi-mode-Allows multiple modes of light to propagate through the fiber. Often use for workgroup applications. Uses light-emitting diodes (LEDs) as light generating device.Fiber optic cables are far more costly than UTP.
23 Optical Fiber - Advantages Greater capacityData rates of hundreds of GbpsSmaller size & weightLower attenuation (signal loss)Greater repeater spacing10s of km at leastNo crosstalk (no light leaking)Electromagnetic isolationhighly secure (no light leaking)
24 Optical Fiber - Disadvantages Not easy to install and maintainUnidirectional, two fibers are needed for bidirectionalCost: more expensive interfaces than electrical interfaces used with other types (twisted, coaxial)
33 Radio waves30MHz to 1GHzOmnidirectional (signal propagates in all directions)Easily interfere with other signals sent at the same frequency rangeCan penetrate walls and can be received in the buildingDoes not require dish-shaped antennasBroadcast radio (AM,FM) ,TV, cordless phone, Paging, cellular phones
34 NoteRadio waves are used for multicast communications, such as radio and television, and paging systems.
35 Microwaves2GHz to 300GHzHighly directional (line-of-sight propagation = straight lines)Requires dish-shaped antennasPoint to point (sending and receiving antennas need to be aligned)Very high frequency microwaves, usually, cannot penetrate walls (disadv. if receivers are inside buildings)Used in long distance telephone communicationsUsed for short point-to-point transmission between buildings to connect their LANsUsed in Wireless networks, satellite communication
36 NoteMicrowaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.
37 Infrared300GHz to 400THzHave a very large bandwidth that is not yet completely utilizedLocal- short distance communicationLine-of-sight propagation (directional)Used in local point-to-point Transmission or Multipoint within a very limited area (single room)Used in Remote control, IrDA (Infrared Data Association) port (wireless keyboard, mouse)Cannot be used under the sun because of the interference with the sun infrared raysIrDA operates at 75kbps up to 8 meters, and 1.15Mbps – 4Mbps over a distance of 1 meter
38 NoteInfrared signals can be used for short-range communication in a closed area using line-of-sight propagation.