The physical layer defines the electrical and mechanical standards for transmitting raw data over a physical medium. It specifies parameters like connector types, transmission frequencies, and line codes. The physical layer sends and receives bits and defines how 0s and 1s are encoded in signals. It translates logical communications from higher layers into specific hardware operations to transmit or receive electronic signals over the transmission medium. The physical layer supports higher layers and interfaces with the data link layer to perform tasks like symbol encoding and transmission.
1. 18CSC302J – Computer Networks
Unit – V
D.Kavitha,
AP/CSE
SRMIST,RMP campus
SRM Institute of Science and Technology 1
2. SRM Institute of Science and Technology 2
Physical layer overview
The physical layer provides an electrical, mechanical, and procedural interface to the
transmission medium.
The shapes and properties of the electrical connectors, the frequencies to broadcast on,
the line code to use and similar low-level parameters, are specified by the physical layer.
Physical Layer is the bottom-most layer in the Open System Interconnection (OSI)
Model which is a physical and electrical representation of the system.
It consists of various network components such as power plugs, connectors, receivers,
cable types, etc. Physical Layer sends data bits from one device(s) (like a computer) to
another device(s).
Physical Layer defines the types of encoding (that is how the 0’s and 1’s are encoded in
a signal). Physical Layer is responsible for the communication of the unstructured raw
data streams over a physical medium.
3. Role of physical layer
The physical layer defines the means of transmitting a stream of raw bits over a physical
data link connecting network nodes. The bitstream may be grouped into code words or
symbols and converted to a physical signal that is transmitted over a transmission
medium.
The physical layer consists of the electronic circuit transmission technologies of a
network . It is a fundamental layer underlying the higher level functions in a network, and
can be implemented through a great number of different hardware technologies with
widely varying characteristics.[4]
Within the semantics of the OSI model, the physical layer translates logical
communications requests from the data link layer into hardware-specific operations to
cause transmission or reception of electronic (or other) signals .The physical layer
supports higher layers responsible for generation of logical data packets.
4. Physical signaling sublayer
In a network using Open Systems Interconnection (OSI) architecture, the physical
signaling sublayer is the portion of the physical layer that
•interfaces with the data link layer's medium access control (MAC) sublayer,
•performs symbol encoding, transmission, reception and decoding and,
•performs galvanic isolation.
5. Relation to the Internet protocol suite
The Internet protocol suite, as defined in RFC 1122 and RFC 1123, is a high-level
networking description used for the Internet and similar networks.
It does not define a layer that deals exclusively with hardware-level specifications and
interfaces, as this model does not concern itself directly with physical interfaces.
