29-09-2016, 11:28 AM
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Physical layer
Physical layer in the OSI model plays the role of interacting with actual hardware and signaling mechanism. Physical layer is the only layer of OSI network model which actually deals with the physical connectivity of two different stations. This layer defines the hardware equipment, cabling, wiring, frequencies, pulses used to represent binary signals etc.
Physical layer provides its services to Data-link layer. Data-link layer hands over frames to physical layer. Physical layer converts them to electrical pulses, which represent binary data.The binary data is then sent over the wired or wireless media.
signals
When data is sent over physical medium, it needs to be first converted into electromagnetic signals. Data itself can be analog such as human voice, or digital such as file on the disk.Both analog and digital data can be represented in digital or analog signals.
Digital Signals
Digital signals are discrete in nature and represent sequence of voltage pulses. Digital signals are used within the circuitry of a computer system.
Analog Signals
Analog signals are in continuous wave form in nature and represented by continuous electromagnetic waves.
Physical Media
Physical link: Transmitted data bit propagates across link
Guided media:
Signals propagate in solid media: copper, fiber
Unguided media:
Signals propagate freely, e.g., radio
Twisted pair(TP)
Two insulated copper wires
Category 3: traditional phone wires, 10 Mbps ethernet
Category 5 TP: 100Mbps ethernet