Physical Layer - Layer 1 of OSI model

- The physical layer is level one in the seven level OSI model. Actually, it is last layer that receives and processes the data from the sending device while it is first layer to receive the data at the destination end.
- It performs services requested by the data link layer.
- The Physical Layer defines the Mechanical, Electrical, Procedural and Functional specifications for activating, maintaining and deactivating the physical link between communication network systems.
- The basic objective of this layer is to transform the data in the form that is needed to be carried through the transmission media over the network. The transmission media either bounded or unbounded , carries the data in the form of electromagnetic waves or radio waves.
- The Physical Layer is responsible for bit-level transmission between network nodes.
The main functions of physical layer are :

- Definition of Hardware Specifications: The details of operation of cables, connectors, wireless radio transceivers, network interface cards and other hardware devices are generally a function of the physical layer. Devices used in the Physical Layer are
* Network Interface Cards (NIC)
* Transceivers
* Repeaters
* Hubs
* Multi Station Access Units (MAU’s)
- Encoding and Signaling: The physical layer is responsible for various encoding and signaling functions that transform the data from bits that reside within a computer or other device into signals that can be sent over the network.
- Data Transmission and Reception: After encoding the data appropriately, the physical layer actually transmits the data, and of course, receives it.
- Topology and Physical Network Design: The physical layer is also considered the domain of many hardware-related network design issues, such as LAN and WAN topology. There are four possible kinds of topologies:
* Bus
* Star
* Ring
* Mesh
In general, then, physical layer technologies are ones that are at the very lowest level and deal with the actual ones and zeroes that are sent over the network.