Physical Layer

Physical Layer

In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first (lowest) layer.  The implementation of this layer is often termed PHY.  Transmission and receipt of data from the physical medium (copper wire, fiber, radio frequencies, barbed wire, string etc.) is managed at this layer. Within the semantics of the OSI network architecture, the physical layer translates logical communications requests from the data link layer into hardware-specific operations to affect transmission or reception of electronic signals.

The Physical Layer receives data from the data link Layer, and transmits it to the wire. The physical layer controls the electrical and mechanical functions related to the transmission and receipt of a communications signal. It also manages the encoding and decoding of data contained within the modulated signal.

Note that for two devices to communicate, they must beconnected to the same type of physical medium (wiring). 802.3 Ethernet to 802.3 Ethernet, FDDI to FDDI, serial to serial etc. Two end stations using different protocols can only communicate through a multi-protocol bridge or a router.

The physical layer is responsible for:

Communication with the data link layer above it.

Fragmentation of data into frames

Reassembly of frames into data link Protocol Data Units.

Transmission to the physical media

Receiving from the physical media

It should be noted that in most modern network interface adaptors, the physical and data link functions are performed by the adaptor.

Example Physical Protocols

CSMA/CD - Carrier Sense Multiple Access / Collision Detect

CSMA/CA - Carrier Sense Multiple Access / Collision Avoid

FDMA - Frequency Division Multiple Access

MSK - Minimum Shift Keying

GFMSK - Gaussian-Fitered Minimum Shift Keying

TDMA - Time Division Multiple Access

CDMA - Code Division Multiple Access

B8ZS - Binary 8 Zero Substitution

2B1Q - 2 Binary 1 Quaternary

PCM - Pulse Code Modulation

QAM - Quadrature Amplitude Modulation

PSK - Phase Shift Keying

SONET - Synchronous Optical NETworking

  

At the Physical layer, data are transmitted using the type of signaling supported by the physical medium:

Ø  electric voltages

Ø  radio frequencies

Ø  pulses of infrared or ordinary light

Referensi :

• ·         http://en.wikipedia.org/wiki/Physical_layer
• ·         http://www.erg.abdn.ac.uk/~gorry/eg3561/phy-pages/phy.html
• ·         http://compnetworking.about.com/od/basicnetworkingconcepts/l/blbasics_osi1.htm
• ·         http://www.techopedia.com/definition/8866/physical-layer
• ·         http://www.inetdaemon.com/tutorials/basic_concepts/network_models/osi_model/physical.shtml
• ·         http://www.idt.com/products/interface-connectivity/physical-layer-products
• ·         http://www.tcpipguide.com/free/t_PhysicalLayerLayer1.htm
• ·         http://www.mrv.com/tap/physical-layer/
• ·         http://www.ti.com/analog/docs/microsite.tsp?sectionId=585&tabId=2203&micrositeId=10
• ·         http://www.can-cia.org/index.php?id=systemdesign-can-physicallayer