Networks rely on multiplexing to increase the amount of data that can be transmitted in a given time span over a given bandwidth - Time division multiplexing (TDM) o Divides channel into multiple time intervals • Statistical multiplexing – Transmitter assigns slots to nodes
• According to priority, need – More efficient than TDM • Frequency division multiplexing (FDM) – Unique frequency band for each communications subchannel – Cellular telephone transmission – DSL Internet access • Wavelength division multiplexing (WDM) – One fiber-optic connection – Carries multiple light signals simultaneously • Dense wavelength division multiplexing (DWDM) – Used on most modern fiber-optic networks – Extraordinary capacity Networking Media - Match networking needs with media characteristics when selecting transmission media • Physical media characteristics: Throughput, Cost, Noise immunity, Size and scalability, Connectors and media converters Throughput: • Most significant factor in choosing transmission method • Causes of throughput limitations – Laws of physics – Signaling and multiplexing techniques – Noise – Devices connected to transmission medium • Fiber-optic cables allow faster throughput – Compared to copper or wireless connections
Cost: • Precise costs difficult to pinpoint • Media cost dependencies – Existing hardware, network size, labor costs • Variables influencing final cost – Installation cost – New infrastructure cost versus reuse – Maintenance and support costs – Cost of lower transmission rate affecting productivity – Cost of downtime – Cost of obsolescence Noise Immunity: • Noise distorts data signals – Distortion rate dependent upon transmission media • Fiber-optic: least susceptible to noise • Limit noise impact on network – Cable installation • Far away from powerful electromagnetic forces – Select media protecting signal from noise Size and Scalability: • Three specifications – Maximum nodes per segment – Maximum segment length – Maximum network length • Maximum nodes per segment dependency – Attenuation and latency • Maximum segment length dependency – Attenuation and latency plus segment type • Segment types – Populated: contains end nodes – Unpopulated: no end nodes • Also called link segment • Segment length limitation – After certain distance, signal loses strength • Cannot be accurately interpreted Connectors and Media Converters: • Connectors – Hardware connecting wire to network device – Specific to particular media type – Affect costs • Installing and maintaining network • Ease of adding new segments or nodes • Technical expertise required to maintain network • Media converter – Hardware enabling networks or segments running on different media to interconnect and exchange signals Cabling Coaxial Cable: • Central metal core (often copper) surrounded by: – Insulator – Braided metal shielding (braiding or shield) –
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- Fall '12
- Twisted pair, Coaxial cable