Data Communications Notes
Transmission Media
• Transmission medium – Physical path between transmitter and receiver – May be guided (wired) or unguided (wireless) – Communication achieved by using em waves • Characteristics and quality of data transmission – Dependent on characteristics of medium and signal – Guided medium ∗ Medium is more important in setting transmission parameters – Unguided medium ∗ Bandwidth of the signal produced by transmitting antenna is important in setting transmission parameters ∗ Signal directionality · Lower frequency signals are omnidirectional · Higher frequency signals can be focused in a directional beam • Design of data transmission system – Concerned with data rate and distance – Bandwidth ∗ Higher bandwidth implies higher data rate – Transmission impairments ∗ Attenuation ∗ Twisted pair has more attenuation than coaxial cable which in turn is not as good as optical fiber – Interference ∗ Can be minimized by proper shielding in guided media – Number of receivers ∗ In a shared link, each attachment introduces attenuation and distortion on the line
Guided transmission media • Transmission capacity (bandwidth and data rate) depends on distance and type of network (point-to-point or multipoint) • Twisted pair – Least expensive and most widely used – Physical description ∗ Two insulated copper wires arranged in regular spiral pattern ∗ Number of pairs are bundled together in a cable ∗ Twisting decreases the crosstalk interference between adjacent pairs in the cable, by using different twist length for neighboring pairs – Applications ∗ Most common transmission media for both digital and analog signals
Transmission Media
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∗ Less expensive compared to coaxial cable or optical fiber ∗ Limited in terms of data rate and distance ∗ Telephone network · Individual units (residence lines) to local exchange (end office) · Subscriber loops · Supports voice traffic using analog signaling · May handle digital data at modest rates using modems ∗ Communications
• Transmission medium – Physical path between transmitter and receiver – May be guided (wired) or unguided (wireless) – Communication achieved by using em waves • Characteristics and quality of data transmission – Dependent on characteristics of medium and signal – Guided medium ∗ Medium is more important in setting transmission parameters – Unguided medium ∗ Bandwidth of the signal produced by transmitting antenna is important in setting transmission parameters ∗ Signal directionality · Lower frequency signals are omnidirectional · Higher frequency signals can be focused in a directional beam • Design of data transmission system – Concerned with data rate and distance – Bandwidth ∗ Higher bandwidth implies higher data rate – Transmission impairments ∗ Attenuation ∗ Twisted pair has more attenuation than coaxial cable which in turn is not as good as optical fiber – Interference ∗ Can be minimized by proper shielding in guided media – Number of receivers ∗ In a shared link, each attachment introduces attenuation and distortion on the line
Guided transmission media • Transmission capacity (bandwidth and data rate) depends on distance and type of network (point-to-point or multipoint) • Twisted pair – Least expensive and most widely used – Physical description ∗ Two insulated copper wires arranged in regular spiral pattern ∗ Number of pairs are bundled together in a cable ∗ Twisting decreases the crosstalk interference between adjacent pairs in the cable, by using different twist length for neighboring pairs – Applications ∗ Most common transmission media for both digital and analog signals
Transmission Media
25
∗ Less expensive compared to coaxial cable or optical fiber ∗ Limited in terms of data rate and distance ∗ Telephone network · Individual units (residence lines) to local exchange (end office) · Subscriber loops · Supports voice traffic using analog signaling · May handle digital data at modest rates using modems ∗ Communications