Physical Layer

The physical layer is the lower most layer in OSI model which deal with raw data transmission. Physical layer provides electrical, mechanical, functional and procedural means to activate, maintain and deactivate physical connections for bit transmission between data link entities.

Physical Layer Defines:

Mechanical

Medium
A transmission medium is any material substance which can propagate waves or energy. The media can be broadly classified as Guided and unguided.
Guided: Copper, Fiber
Unguided: Infrared, radio, Microwave

Connectors
An electrical connector is a device for joining electrical circuits together.
Ex: DB25, DB9, DIN, RJ-45

Topology:

The physical or logical shape of the network.

Ex: Star, Ring, Bus

Electrical

Line Coding
The waveform pattern of voltage or current used to represent the 1s and 0s of a digital signal on a transmission link is called line encoding.
Ex: NRZ, 2B1Q, 4B45B, AMI

Modulation
Process by which an information signal is used to modify some characteristic of a higher frequency wave known as a carrier.
Ex: AM, FM, FSK, PCM

Multiplexing
Multiplexing is a term used to refer to a process where multiple analog message signals or digital data streams are combined into one signal.
Ex: TDM, FDM, CDMA, WDM

Procedural

Transmission Mode
Synchronous or Asynchronous

Transmission Direction
Simplex, Half Duplex or Full Duplex

Communication Mode
Serial or Parallel

Line Configuration

Point-Point, multipoint, or point-multipoint

Error Control
Parity bits and CRC

Media Control
Carrier Sensing and Collision detections

Physical Layer Protocols:

X.21, X.21 bis, V.90, V.92

RS232, EIA442, EIA423, RS449, RS485

ISDN, B-ISDN, DSL, xDSL

SDH/SONET, T1/E1

10BASE-T, 10BASE2, 10BASE5, 100BASE-TX, 100BASE-FX, 100BASE-T, 1000BASE-T, 1000BASE-SX physical layers

IrDA, Wi-Fi, GSM, CDMA, Blutooth physical layers