OSI Layer 1 – Physical

Layer 1 of the OSI model is the Physical layer (PHY).

responsible for the transmission and receipt of signals that represent bits of data
transmission media can be:
- cabled — physical signal conductor between nodes
  - aka bounded media
- wireless — uses free space between nodes
  - aka unbounded media

Components of Physical Layer

Physical topology
- the layout of nodes and links established by the transmission media
- an area of a larger network is called a segment
  - a segment is where all the nodes share access to the same media
  - network is divided into segments to:
    - cope with physical restrictions of the network media
    - improve performance
    - improve security
Physical interface
- mechanical specifications for the network medium
- for cabled media:
  - the construction of the cable
  - the interface/connector form factor
  - the number and functions of the pins in a connector
- for wireless media:
  - the radio transceiver and antenna specifications
Signaling
- the process of transmitting and receiving encoded data over the network medium
- modulation scheme describes how electrical, light, or radio signal represent bits
- timing and synchronization schemes ensure senders and receivers can identify groups of signals as a chunk or frame of data

Transceiver — The part of a network interface that sends and receives signals over the network
Repeater — A device that amplifies an electronic signal to extend the maximum allowable distance for a media type
Hub — A multiport repeater, deployed as the central point of connection for nodes
Media converter — a device that converts one media signaling type to another