Layer 1 of the OSI model or we know it OSI Physical Layer controls how data is transmitted on the communication media. Physical layers usually use copper cable, wireless and fiber as the basic form of network media. And this make the main purpose of this layer is to create the electrical, microwave or optical signals that represent the bits in each frame.
OSI physical layer has three fundamental functions such the physical components, data encoding and signaling. The physical elements are about the hardware devices such electronic, media and connectors devices that transmit and carry the signals to represent the bits. Encoding is about method to knowing a stream of data bits. Signaling is about generating electrical, wireless or optical signal that represent by 0 or 1 and what it means. Another important topic in OSI physical layers is about speed of data transfer that can be measured by bandwidth, throughput and goodput. Digital bandwidth measures the amount of information that can flow from 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. Goodput is the measure of usable data transferred over a given period of time, and is therefore the measure that is of most interest to network users.
OSI physical layer is concerned with network media. Today mostly used network media is cable, wireless and optical media. Cable mostly used is UTP (Unshield Twisted Pair), wireless mostly used is WLAN 802.11a, b, g, n, and gsm, gprs or cdma. Fiber optic cables can be broadly classified into two types: single-mode and multimode.