Physical layer
The
physical layer is level one in the seven level
OSI model of
computer networking. It performs services requested by the
data link layer.
This level refers to network
hardware, physical cabling or a wireless
electromagnetic connection. It also deals with electrical specifications,
collision control and other low-level functions.
The physical layer is the most basic network layer, providing only the means of transmitting raw bits. The shapes of the
electrical connectors, which frequencies to broadcast on, and similar low-level things are specified here. An analogy of this layer in a physical mail network would be a specification for various kinds of paper and ink, for example.
The major functions and services performed by the physical layer are:
* establishment and
termination of a connection to a
communications medium;
* participation in the process whereby the communication resources are effectively shared among multiple users,
e.g., contention resolution and
flow control;
* conversion between the representation of
digital data in
user equipment and the corresponding signals transmitted over a communications
channel.
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* performs
character encoding,
transmission,
reception and decoding
* performs optional isolation functions.
Source: from
Federal Standard 1037C*
EIA standards:
RS-232,
RS-422,
RS-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 Ethernet* Varieties of
802.11*
SONET/SDH*
Repeater*
Ethernet hub*
ModemNote: Physical layerAssociated with transmission of unstructured bit streams over a physical link.Responsible for the mechanical, electrical and procedural characterstics thatestablish, maintain and deactivate the physical link.
*
Ethernet physical layer*
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