Terminology (1) Data transmission occurs between transmitter and receiver over some transmission medium Signal: electromagnetic waves -Can propagate along the transmission medium Transmission medium -Guided medium: the signals are guided along a physical path e.g, twisted pair, coaxial cable, optical fiber -Unguided medium: wireless e.g., air, water, vacuum
6 Terminology (1) • Data transmission occurs between transmitter and receiver over some transmission medium. • Signal: electromagnetic waves —Can propagate along the transmission medium • Transmission Medium —Guided medium: the signals are guided along a physical path • e.g., twisted pair, coaxial cable, optical fiber —Unguided medium: wireless • e.g., air, water, vacuum
Terminology(2) · Direct link Refer to the transmission path between the transmitter and receiver in which signals propagate directly with no intermediate devices, other than amplifiers or repeaters used to increase signal strength Note that it can apply to both guided and unguided media A transmission medium is point-to-point if Point-to-point -Direct link Only 2 devices share the medium a transmission medium is multipoint if More than two devices share the same medium Multipoint
7 Terminology (2) • Direct link —Refer to the transmission path between the transmitter and receiver in which signals propagate directly with no intermediate devices, other than amplifiers or repeaters used to increase signal strength. —Note that it can apply to both guided and unguided media • A transmission medium is point-to-point if: —Direct link —Only 2 devices share the medium • A transmission medium is multipoint if: —More than two devices share the same medium Point-to-point Multipoint
Terminology (3) Simplex transmission -Signals are transmitted in only one direction e.g. Television · Half duplex -Signals can be transmitted in either direction, but only one way at a time e.g. police radio Full duplex -Both stations may transmit simultaneously e.g. telephone 8
8 Terminology (3) • Simplex transmission —Signals are transmitted in only one direction • e.g. Television • Half duplex —Signals can be transmitted in either direction, but only one way at a time. • e.g. police radio • Full duplex —Both stations may transmit simultaneously. • e.g. telephone
Signals: Time Domain We are concerned with electromagnetic signals used as a means to transmit data A signal is generated by the transmitter and transmitted over a medium The signal is a function of time but it can also be expressed as a function of frequency Time domain concepts: an electromagnetic signal can be either analog or gita Analog signal The signal intensity varies in a smooth fashion over time. Or, there is no breaks or discontinuities in the signal Digital signal The signal intensity maintains a constant level for some period of time and then changes to another constant level Time domain function of a signal: s(t/ pecifies the amplitude(in volts )of the signal at each instant in time 9
9 Signals: Time Domain • We are concerned with electromagnetic signals used as a means to transmit data. • A signal is generated by the transmitter and transmitted over a medium. • The signal is a function of time, but it can also be expressed as a function of frequency. • Time domain concepts: an electromagnetic signal can be either analog or digital — Analog signal • The signal intensity varies in a smooth fashion over time. Or, there is no breaks or discontinuities in the signal. — Digital signal • The signal intensity maintains a constant level for some period of time and then changes to another constant level. • Time domain function of a signal: s(t) — Specifies the amplitude (in volts) of the signal at each instant in time
Analogue Digital signals Amplitude (volts) (a)Analog Amplitude Time 10 Digital
10 Analogue & Digital Signals