Physical layer Totally Explained

Everything about Physical Layer totally explained

The physical layer is the first level in the seven-layer OSI model of computer networking as well as in the five-layer TCP/IP reference model. It performs services requested by the data link layer.
The physical layer is the most basic network layer, providing only the means of transmitting raw bits rather than packets over a physical data link connecting network nodes. No packet headers nor trailers are consequently added to the data by the physical layer. The bit stream may be grouped into code words or symbols, and converted to a physical signal, which is transmitted over a physical transmission medium. The physical layer provides an electrical, mechanical, and procedural interface to the transmission medium. The shapes of the electrical connectors, which frequencies to broadcast on, what modulation scheme to use and similar low-level parameters are specified here. An analogy of this layer in a physical mail network would be the roads along which the vans carrying the mail drive.

Physical signaling sublayer

In a local area network (LAN) or a metropolitan area network (MAN) using open systems interconnection (OSI) architecture, the physical signaling sublayer is the portion of the physical layer that:

interfaces with the medium access control sublayer (MAC) which is a part of the Data Link Layer
performs character encoding, transmission, reception and decoding
performs mandatory isolation functions.

Source: from Federal Standard 1037C RAJESH KRISHNAN

List of physical layer services

The major functions and services performed by the physical layer are:

Bit-by-bit delivery

Providing a standardized interface to physical transmission media, including

Mechanical specification of electrical connectors and cables, for example maximum cable length
Electrical specification of transmission line signal level and impedance
Radio interface, including electromagnetic spectrum frequency allocation and specification of signal strength, analog bandwidth, etc.
Specifications for IR over optical fiber or a wireless IR communication link

Modulation

Line coding

Bit synchronization in synchronous serial communication

Start-stop signalling and flow control in asynchronous serial communication

Circuit mode multiplexing, as opposed to statistical multiplexing performed at the higher level

Establishment and termination of circuit switched connections

Carrier sense and collision detection utilized by some level 2 multiple access protocols

Equalization filtering, training sequences, pulse shaping and other signal processing of physical signals

Forward error correction, for example bitwise convolutional coding

Bit-interleaving and other channel coding The physical layer is also concerned with

Point-to-point, multipoint or point-to-multipoint line configuration

Physical network topology, for example bus, ring, mesh or star network

Serial or parallel communication

Simplex, half duplex or full duplex transmission mode

Autonegotiation

Physical layer examples

V.92 telephone network modems

IRDA physical layer

USB physical layer

Firewire

EIA RS-232, EIA-422, EIA-423, RS-449, RS-485

ITU Recommendations: see ITU-T

DSL

ISDN

T1 and other T-carrier links, and E1 and other E-carrier links

10BASE-T, 10BASE2, 10BASE5, 100BASE-TX, 100BASE-FX, 100BASE-T, 1000BASE-T, 1000BASE-SX and other varieties of the Ethernet physical layer

Varieties of 802.11

SONET/SDH

GSM radio interface

Bluetooth physical layer

IEEE 802.11x Wi-Fi physical layers

Etherloop

Hardware equipment (network node) examples

Network adapter

Repeater

Network hub

ModemFurther Information

Get more info on 'Physical Layer'.

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