| A | B |
|---|
| ISO | International Standards Organisation |
| ITU | International Telecommunications Union |
| EIA | Electronic Industries Association |
| IEEE | Institute of Electrical and Electronic Engineers |
| Standards - Benefits to Customers | ensures product compatablity, increases competition |
| Standards - Benefits to Vendors | Cheaper Production Costs, compliance is a selling point |
| Amplitude | Peak value mesured in volts |
| Period | one complete repitition, measured in seconds |
| Frequency | rate at which signals repeat, measured in hertz |
| Phase | measure of the relative postiion in time within the period of a signal |
| Attenuation | The weakening of the amplitude of a signal transmitted over distance |
| Delay Distortion | is caused when different frequenies travel through media at different speeds. (signal travels slowest at the edge of the mediums bandwidth) |
| Thermal Noise | is cause through the operation of electronic equipment |
| Intermodulation | Causes unwanted signals in the transmission |
| Crosstalk | occurs when signals from adjacent bandwidths interfere with a signal |
| Impulse Noise | caused by power spikes or other random events. Creates a burst of noise that might corrupt bits. |
| Bandwidth | Determines the maximum data rate |
| Serial transmission | Data is transmitted one bit at a time along one channel |
| Parallel Transmission | Many bits transmitted simultaneously along multiple channels |
| Data signal | a varying signal that represents coded information |
| Carrier Signal | A continous constant-frequency signal being sent through a communicationd channel. IIt is used to suplly energy to transmit the data signal |
| Modulation | the process of using data signals to modify the carrier signal |
| Demodulation | the process of deducing the data signal from the modified carrier signal |
| Modem | Is used to modulate a data signal to be transmitted and to demodulate a received signal |
| Codec | Is used to convert an analog signal into a digital bit stream and vice versa |
| Quadrature Amplitude Modulation (QAM) | Combination of amplitude modulation and phase modulation. It can carry more bits per baud, whihc increases the data rate. |
| Manchester | Uses two voltage levels, with a transition at the mid point of each bit perios |
| AM (Amplitude Modulation) | A transmission technique that alters the amplitude of a sine wave |
| Differential Manchester | Transition at the beginneg of a bit period indicates a 0 and the absenbce of a transition indicates a 1 |
| Amplitude Shift Keying (ASK) | A technique that modulates a signal above and below a control reference amplitude |
| NRZ-L (non return to Zero - level) | 2 voltage levels are used, a negative represents 0, positive a 1 |
| FSK (Frequency Shift Keying) | A technicque that modulates a signal above and below a central refernce frequency |
| Frequency Modulation (FM) | Alters the frequency of a sine wave while the amplitude is constant. |
| Phase Shift Keying (PSK) | A technique that modulates a signal by shiftng the phase of the sine wave representing the data |
| Pulse Code Modulation (PCM) | An analog signal is sampled by taking measurements at a rate at least twice the highest frequency signal, and transmitted as binary numbers. It is used by the receiver to construct a copy. |
| Phase Modulation (PM) | A method of modulation where the amplitude of the modulated wave remains constant while varying in phase |
| Multiplexing | allows the simultaneous transmission of multiple signals across a single data link |
| Multiplexing Techniques | FDM, TDM, Stat TDM, Syn TDM, Async TDM |
| OSI | open Systems Interconnection |
| Seven Layers of the OSI Model | Physical, Data Link, Network, Transport, Session, Presentation, Application |
| Flow Control is | a technique of limiting the amount of data sent by a transmitting device |
| Channel Capacity depends on | Data Rate, bandwidth, noise, and error rate |
| The four attributes of a channel are | Bandwidth, media, data transmission speed, Direction of transmission |
| Advantages of Fibre optic over copper cable: | greater bandwidth / data rate, better data security, less susceptible to EMI (electromagnetic interference), lighter wieght and smaller size |
| Factors limiting data transmission rate | Attenuation, bandwidth, Noise |
| Free-space loss | signal disperses over distance |
| Multipath | relfection of signal from obstacles such as buildings, resulting in in copies with varying delays |
| Refraction | Caused by changes in the speed of the signal with altitude |
| Guided Media impairments | Attenuation, attenuation distortion, delay distortion, noise |
| Unguided media impairments | free-space loss, atmospheric absorption, multipath, refraction, thermal noise |
| Attenuation Distortion | attenuation at higher frequencies (mainly affects analog) |
| Delay Distortion | propagation rate different at different frequencies (mainly affects digital) |
| Asynchronous Transmission | receiver and transmitter clocks run independently during transmission |
| Synchronous Transmission | adjusting the receivers clock during transmission |
| Isochronous | use the same clock |
| What is asynchronous transmission | the transmission of one character at a time, with synchronisation occuring at every byte, independant of clock timing |
| What is Synchronous Transmission? | Blocks of data are transmitted with the send and receiver being synchornised by a clock timing device |
| Flow Control | is a technique limiting the amount of data snet by a transmitting device (Stop-and-wait flow control and Sliding-window flow control) |
| Stop-and-wait flow control | Tx must wait until it receives an ACK before sening the next frame |
| Sliding-window flow control | Rx receives multiple frames before sending an ACK, Tx maintains a sequence number (each frame has a sequence number) |
| ACK | positive acknowledgement |
| Error Control | involves Error detection, and error correction |
| Parity check | detects only a single bit error |
| Cyclic Redundancy Check (CRC) | Treats a frame as one long binary number, and divides the frame by a prime binary number. The remainder is atached to each frame transmitted |
| Forward Error Control (FEC) | Each transmitted frame contains addition (redundant) information so that the receiver can detect when and where errors are present. |
| Trellis Coding | A technique which uses forward error correction, which allows error detection and correction without the need to retransmit data. |
| Analog Tansmission of analog data | AM (Amplitude Modulation), Frequency Modulation (FM), Phase Modulation (PM) |
| Digital Transmission of analog data, | Pulse Code Modulation (PCM) |
| Digital transmission of digital data, | Manchester, Differential Manchester, NRZ-L (non return to Zero - level) |
| Analog transmission of digital data. | FSK (Frequency Shift Keying), Phase Shift Keying (PSK), Amplitude Shift Keying (ASK) |
| Four main parts of the EIA (RS) 232 standard | Mechanical description of interface circuits, Electrical signal characteristics, Functional description of interface circuits, Procedural description of Interface Circuits. |
| Where are CRC's (Cyclic Redundancy Checks) used? | LANS and WANS |
| Where is flow control used? | Satelitte Links, Live Television broadcasts |
| What are the 3 Points of Shannons Thereom | Channel capacity is directly proportional to bandwidth and signal power; channel capacity is inversly proportional to noise. |
| What is the Mechanical Sepecification of the EIA 232 responsible for? | This describes the 25-pin connector with a speicific arrangment of leads. |
| What is the purpose of the Electrical Specification of the EIA 232? | This sepcifies the signalling between the DTE and the DCE |
| What is the purpose of the Functional Specification of the EIA 232? | This specifies the funcction that is performed by each of the pins on the connector. |
| What is the prupose of the Procedural Specification of the EIA 232? | This specifies the sequence for transmitting data, based on the functional characteristics of the connector. |
