Layer 1 - Physical layer

The Physical layer concerns itself with the transmission of bits and the network card's hardware interface to the network. The hardware interface involves the type of cabling (coax, twisted pair, etc..), frequency of operation (1 Mbps, 10Mbps, etc..), voltage levels, cable terminations, topology (physical shape of the network: star, bus, ring, etc..), etc.. Examples of Physical layer protocols are 100BaseT, 1000BaseT, Token Ring... See Fig. 1.

Fig. 1 Physical Layer

The Layer 1 - Physical section is divided into the following sections:

Physical Aspects of the Media - When we look at the Data Communications model, we see that all communications must travel through some sort of medium. The Physical layer of the OSI model is concerned with the physical attributes of the medium such as cable type, frequency, voltages, etc.... This section describes the physical aspects of the medium and how it affects the transfer of data.

Line Encoding - In transmitting data , there must be a method of representing the digital logic levels using the physical attributes associated with the media. Line encoding is the method used to represent the digital information on the media.

Digital Codes - This section looks at how information, such as alphanumeric characters, that we, as human beings, understand are represented digitally by the computer.

Timing - This section discusses two different methods of transmitting data through the media so that the destination station reliably receives the data. Timing refers to the method used by the data communication system so that the destination station recognizes the start of a data stream and reliably reads the information sent.

Repeaters - The purpose of a repeater is to extend the LAN Segment beyond its physical limits as defined by the Physical Layer's Standards

Hubs - These devices are also called Multiport Repeaters or Concentrators. They are physical hardware devices that are used to provide a Physical Star Topology.

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Copyright July 2013 Eugene Blanchard