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Unformatted text preview: IST 233 Exam 2 Study Guide Chapter 5: Physical Layer Propagation Propagation and Signals • Propagation: the traveling of a signal down a transmission medium • Signal: a disturbance that propagates down a transmission medium to the other side, which reads the signal • Propagation effects: changes in the signal during propagation o Attenuation – signal weakens o Distortion – shape has been changed o Interference - o If propagation effects are too large, the receiver will not be able to interpret the signal correctly • Noise – random electromagnetic energy within wires; combines with the data signal to make the data signal difficult to read • Signal-to-noise ration (SNR) – the ratio of the signal strength to average noise strength; should be high in order for the signal to be effectively received o High ratio = signal far larger than the noise floor § Noise floor – average noise level How do propagation effects differ based on the type of media used? What are the three major types of media used on today’s computer networks? Briefly explain their advantages and disadvantages of each one. Signaling • Analog – signal rises and falls smoothly in intensity o Small propagation errors are not fixed • Binary – two states per clock cycle o Small propagation effects do not create errors in reading the signal o Large propagation can render signal totally unrecognizable • Digital – more than 2 states per clock cycle o Transmits multiple bits per clock cycle o Less immunity to propagation errors than binary transmission • Today most signaling is binary 4-pair Unshielded Twisted Pair (UTP) • Inexpensive, widely available and relatively easy to install • Rugged – tough and durable • Dominates media for access links between a host and the nearest switch o Ethernet LANs typically use this wiring to connect to the nearest switches • Not all UTP cables are created equally How many twisted pair strands are required for a traditional telephone connection? For an Ethernet connection? Standards and Limitations/Connectorizing • Ethernet standards limits UTP cords to 100 meters at all speeds up to 1 Gbps o Signal still will be comfortably larger than noise floor so there are few noise errors • UTP is easy to connectorize (add more connectors) Crosstalk Interference • Mutual interference among wire pairs in a UTP cord • Always present in wire bundles • The twisting of each pair normally keeps interference to a negligible level Terminal Crosstalk Interference • Crosstalk interference at the ends of the UTP cord • Usually much larger than the rest of the crosstalk interference over the rest of the cord Minimizing Impact of Crosstalk Interference • Twisting automatically mitigates the effect • Installers must be careful not to untwist UTP wires more than 1.25 cm (1/2 inch) when adding connectors • Precaution will not completely eliminate interference, but limit to an acceptable level Serial and Parallel Transmission • Serial – Ethernet transmission over a single pair in each direction •...
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This note was uploaded on 02/07/2012 for the course IST 195 taught by Professor Staff during the Spring '08 term at Syracuse.
- Spring '08