S305 WEEK 4/5

Vocabulary practice flashcards covering physical transmission media, modulation schemes, multiplexing, digital versus analog signaling, and Layer 1 networking principles.

Shielded Twisted-Pair (STP) Cabling

A type of cabling distinguished by a metallic foil or braided shield wrapped around the wire pairs to provide extra protection against interference.

Bipolar Signaling

A transmission method that uses positive and negative voltages (e.g., $+5\,\text{V}$ and $-5\,\text{V}$); it is less prone to transmission errors than unipolar signaling because detecting a polarity change is easier for receivers.

Dispersion

The spreading out of light pulses in fiber-optic communications as different rays travel along different path lengths, causing signals to arrive at slightly different times.

Manchester Encoding

A digital encoding method where binary 0 is represented by a high-to-low mid-bit voltage transition and binary 1 is represented by a low-to-high mid-bit transition, providing built-in clock synchronization and reliable error detection.

Wavelength Division Multiplexing (WDM)

A multiplexing technique in fiber-optic circuits that uses different wavelengths (colors) of light generated by lasers or LEDs to separate channels.

Turnaround Time

The time required for a circuit to switch directions between sending and receiving data in half-duplex communications (also called retrain time or reclocking time).

Single-Mode Fiber-Optic Cable

A fiber-optic cable that has a much smaller core ($5\text{ to }10\,\mu\text{m}$) than multimode fiber and uses lasers to send a single direct light ray over long distances.

Microwave Communications

A line-of-sight wireless communication technology requiring elevated towers with parabolic dish antennas to provide clear, unobstructed paths between point-to-point antennas to account for the Earth's curvature.

Multiplexer (MUX)

A device whose primary function is to divide one high-speed physical communication circuit into several lower-speed logical circuits.

Data Rate Formula

$$\text{Data Rate (bps)} = \text{Symbol Rate (symbols/sec)} \times \text{Bits per Symbol}$$

Twisted-Pair (TP) Cabling

Copper cabling where wire pairs are twisted together to reduce electromagnetic interference (EMI) and crosstalk between adjacent wire pairs.

Symbol Rate

The number of symbol state changes made across an analog transmission circuit per second (also known as baud rate).

Point-to-Point Circuit

A circuit configuration that connects dedicated physical media between exactly two devices.

Bipolar RZ (Return-to-Zero)

A signaling scheme where the signal voltage always drops back to zero volts in the middle of each bit period, unlike NRZ (Non-Return-to-Zero) which maintains voltage throughout the bit period.

Inverse Multiplexing (IMUX)

The process of combining several low-speed physical circuits into a single high-speed logical circuit.

Time Division Multiplexing (TDM)

A transmission sharing technique that divides circuit capacity into dedicated, sequential time slots, allowing connected devices to take turns transmitting.

Fiber-Optic Cable (Physical Security)

The physical transmission medium that offers the highest physical security against wiretapping and signal interception.

Coaxial Cable Physical Layers

The four physical layers inside a coaxial cable: 1. Inner copper conductor core, 2. Dielectric insulator, 3. Outer metallic shielding/conductor, and 4. Outer plastic jacket.

Category 5e/6 Maximum Recommended Distance

$100\,\text{meters}$ (approximately $328\,\text{feet}$) without a repeater.

Coding Scheme

A standardized set of rules used in data communications to represent alphanumeric characters and symbols as specific groups of binary bits.

Layer 1 Physical Security

The protection of physical network infrastructure; crucial because unauthorized physical access to servers, network switches, or cabling renders software firewalls and encryption ineffective.

Quantizing Error

The difference between the original continuous analog wave amplitude and the discrete step approximation assigned during Pulse-Code Modulation (PCM) encoding.

8-Bit Coding Scheme

A coding scheme capable of encoding $2^8 = 256$ unique characters.

Wireless (Radiated) Media

The transmission media category that is most susceptible to external noise and experiences the highest error rates.

Quadrature Amplitude Modulation (QAM)

A modulation technique that combines Amplitude Modulation (AM) and Phase Modulation (PM).

Voice over IP (VoIP)

A technology allowing voice communications to run directly over existing Ethernet/IP data networks, eliminating the need to maintain a separate voice network.

Frequency Division Multiplexing (FDM)

A multiplexing method that creates separate logical channels by dividing a large frequency spectrum into multiple smaller frequency bands running concurrently.

Serial Transmission Mode

A data transmission mode in which bits are transferred sequentially, one bit at a time, over a single physical wire or path.

Multipoint Circuit Configuration

A shared circuit configuration where multiple computers or devices connect to the same physical circuit and take turns transmitting.

Full-Duplex Data Transmission

A communication mode where data flows simultaneously in both directions over the circuit without turnaround delays.

Guard Bands

Unused frequency ranges placed between channels in Frequency Division Multiplexing (FDM) to prevent adjacent channel interference.

Wave Amplitude

The height or power level of a sound or signal wave, measured in decibels ($\text{dB}$).

Statistical Time Division Multiplexing (STDM)

A variation of TDM that allocates time slots dynamically based on actual usage demand rather than reserving fixed, equal slots for idle devices.

Frequency Shift Keying (FSK)

A modulation technique where different frequencies (number of waves per second) represent binary 0 and binary 1 while amplitude and phase remain constant.

Physical Circuit vs. Logical Circuit

A physical circuit refers to the actual transmission medium (e.g., copper wire, fiber-optic cable) connecting devices, whereas a logical circuit refers to the transmission capacity or channel created over that physical medium.

Amplitude Shift Keying (ASK)

A modulation technique where different wave amplitude levels (heights) represent binary 0 and binary 1 while frequency and phase remain constant.

Modulation Bit-Rate Trade-off

The compromise where increasing the number of bits encoded per symbol increases the data rate, but reduces the signal difference between symbol states, making decoding more prone to errors.

Modem (Modulator/Demodulator)

A device that converts digital computer data into analog signals for transmission over voice telephone circuits.

Wave Frequency

The number of complete wave cycles that pass a point per second, measured in Hertz ($\text{Hz}$).

Pulse-Code Modulation (PCM) Steps

The three-step process for converting analog to digital: 1. Sampling the analog wave at regular time intervals, 2. Measuring pulse amplitude (PAM), and 3. Quantizing amplitude into binary digital values.

256-QAM

A modulation scheme that transmits $8\,\text{bits per symbol}$ corresponding to $2^8 = 256\,\text{states}$.

Parallel Transmission Mode

A transmission mode where multiple bits (e.g., an entire 8-bit character) are sent simultaneously across multiple parallel physical wires; rarely used for long distances due to signal degradation and timing skew.

Quantizing Error Minimization

The two adjustments made to PCM encoding to reduce quantizing error: 1. Increase the sampling frequency (sample more often), and 2. Increase the number of amplitude quantization levels (use more bits per sample).

Layer 1 (The Physical Layer)

The layer of the Internet model responsible for transmitting raw bits across physical media.

Wave Phase

The direction in which a wave begins or its starting point cycle position, measured in degrees ($^\circ$).

Standard North American PCM Bit Rate

The standard required circuit bit rate for telephone networks, calculated as $8,000\,\text{samples/sec} \times 8\,\text{bits/sample} = 64,000\,\text{bps}\ (64\,\text{kbps})$.

Adaptive Differential Pulse Code Modulation (ADPCM)

An encoding technique that reduces bandwidth requirements to $32\,\text{kbps}$ by transmitting only the 4-bit difference between consecutive sample values instead of sending full 8-bit amplitude levels.

Simplex Transmission

A data transmission mode that allows data flow in only one fixed direction, unlike half-duplex which allows transmission in both directions but only one direction at a time.

Phase Shift Keying (PSK)

A modulation method where shifts in the wave's starting direction (e.g., $0^\circ$ versus $180^\circ$) represent binary 0 and binary 1.

Geosynchronous Satellite Communications

A long-distance wireless communication medium whose primary operational disadvantage is significant propagation delay caused by the extreme distance signals must travel into space and back.

Codec (Coder/Decoder)

A device that converts analog voice signals into digital bitstreams for digital transmission.

Unipolar Signaling

A signaling technique where voltage is either zero or positive (e.g., $0\,\text{V} = 0$, $+5\,\text{V} = 1$).

Digital Transmission

The transmission of discrete binary electrical or light pulses representing 0s and 1s, offering lower error rates, higher speeds, greater efficiency, easier encryption, and seamless data integration.

Multipoint Circuit Economic Advantage

The cost benefit of multipoint configurations over point-to-point configurations due to requiring significantly less total cabling, thereby lowering installation and hardware costs.