COMS 113 - Data Communication (chapter 8)

In the previous chapters of Cisco we already tackle about the OSI Model in which the Physical Layer is the first step or the first layer of the model, we all know that it supports the electrical or mechanical interface to the physical medium. Chapter 8 is all about the Physical Layer upon reading it I found out that the chapter explains the purpose, operation, the standards and the basic characteristic of copper, fiber and wireless media of the Physical Layer and how it connects to the data networks. 

This Layer works for the communication and in order to communicate we need to have a signal to connect to network. The physical layer create electrical, optical and microwave signal that represented by the bits from data link layer and bits are encoded for transmission with NRZ (Non-Return to Zero) encoding and ManchesterEncoding, after transmission it will go to its destination. The signal will be sent to the media one at a time. The type of the signal depends on the type of media who carries the signals and it has three basic forms the copper cable media, the fiber media and the wireless media. Copper cable has electrical hazards and the signals are patterns of electrical pulses the example of its connector are RJ-45 and RJ-11. Fiber cables are not electrical conductor and the signals are pattern of Lights, it has low signal loss that can operate with much greater lengths compare to copper cable media, examples of its connectors are Straight-Tip (ST), Subscriber Connector (SC), and LucentConnector (LC). Wireless media is not restricted to conductors of pathways, as are copper and fiber media and the signals are patterns of radio transmissions, some types of wireless connections are Standard IEEE 802.11  Wi-Fi/ Wireless LAN(WLAN)), Standard IEEE 802.15(Wireless Personal Area Network(WPAN), Standard IEEE 802.16 (Worldwide Interoperabilityfor Microwave Access (WiMAX) and Global System for Mobile Communications (GSM). If we all observed the commonly used wireless connection nowadays is Wi-Fi.

 Bits are encoded as symbols to represent encoded data or control information called code group before transmission to its destination. Transferring of data can be measured in three ways: Bandwidth, Throughput and Goodput.  Bandwidth measures the amount of information that can flow one place to another in a given amount of time; Throughput is the measure of the transfer of bits across the media over a given period of time; and Goodput measure of usable data transferred over a given period of time. 

SELECTED TERMS

NRZ(Non-Return to Zero)encoding -  a "0" may be represented by one voltage level on the media during the bit time and a "1" might be represented by a different voltage on the media during the bit time.

Manchester Encoding - uses transitions, or the absence of transitions, to indicate a logic level. For example, a "0" is indicated by a high to low transition in the middle of the bit time. For a "1" there is a low to high transition in the middle of the bit time...

Code group - is a consecutive sequence of code-bits interpreted and mapped as data bit patterns.

Purpose of Physical Layer – It provides the means to transport across the network media the bits that make up a Data Link layer frame.

Operation of the Physical Layer – The media does not carry the frame as a single entity. The media carries signals, one at a time, to represent the bits that make up the frame.

Standards of Physical Layer – It consists of hardware, developed by engineers, in the form of electronic circuitry, media, and connectors. Therefore , it is appropriate that the standards governing this hardware are defined by the relevant electrical and communications engineering organizations.