Chapter 8: PHYSICAL LAYER

                       The purpose of the OSI Physical Layer  is to provide the means to transport across the network media the bits that make up a Data Link Layer transmitted onto the local media.

                                    In Physical Layer there are some following elements:

1.) The physical media and associated connectors.

2.) A representation of bits on the media

3.) Encoding of data and control information

4.) Transmitter and receiver circuitry on the network devices.

                         The job of this Layer is to retrieve these individual signals from the media, restore them to their bit representations, and pass the bits up to the Data Link Layer as a complete frame. Also, this Layer is responsible to create the electrical optical or microwave signal that represents the bits in each frame. These signals are then sent on the media at a time.

                        Physical Layer specifications are applied to areas that include: data to radio signal encoding, frequency and power of transmission, signal reception and decoding requirements, and antenna design and construction.

                        Different physical media transfer of bits at different speeds. data transfer can be measured in three ways such as bandwith, throughput, and goodput.

                       Physical Layer technologies are defined by Organizations such as:

                   ISO - the International Organization for Standardization

                 IEEE - the Institute of Electrical and electronics Engineers

                 ANSI- the American National Standards Institute

                 ITU-  the International Telecommunications Union

            EIA/ TIA- The Electronics Industry Alliance or Telecommunications Industry Association

                  There are four commons data communications standards that apply to wireless media:

1. Standard IEEE 802.15 - Wireless Personal Area Network commonly known as  "bluetooth ".
2. Standard IEEE 802.16 -  WIMAX (Worldwide Interoperability for Microwave Access)
3. Standard IEEE 802.11 - commonly referred to as WI-FI .
4. GSM - (Global System for Mobile Communications).

On the Operation of this Layer, the network media has three basic forms on which the data is represented:

1. Copper cable - the signals are patterns of electrical pulses
2. Fiber- the signals are patterns of light 
3. Wireless Media - the signals are patterns of radio transmission.

In Physical layer there are three fundamentals functions:

1. The physical components
2. Data encoding
3. Signaling