1. Physical Layer

Physical layer, OSI model की पहली व सबसे lowest layer होती है, इसको bit unit layer भी कहते हैं।  यह layer physical व electrical कनेक्शन के लिए जिम्मेदार होती। इस layer मे digital signal, electrical signal में बदल जाता है। यह layer यह भी बताती है कि कनेक्शन wired होगा या वायरलेस।  Physical layer की मुख्य ability अलग-अलग bits को एक नोड से दूसरे नोड में transmit करना है।  यह physical कनेक्शन को establish, maintain व inactive करती है।  इस लेयर में नेटवर्क की topology अर्थात layout of network (नेटवर्क का आकार)  का कार्य भी इसी लेयर में होता है।

Hub, Repeater, Modem, Cables are Physical Layer devices. 
Network Layer, Data Link Layer and Physical Layer are also known as Lower Layers or Hardware Layers.

Examples of hardware in the physical layer are network adapters, ethernet, repeaters, networking hubs, etc.

1. Physical Layer

Physical layer is the first and lowest layer of the OSI model, it is also called bit unit layer. This layer is responsible for physical and electrical connections. In this layer the digital signal is converted into electrical signal. This layer also tells whether the connection will be wired or wireless. The main ability of the physical layer is to transmit different bits from one node to another. It establishes, maintains and deactivates the physical connection. In this layer, the work of topology of the network i.e. layout of the network (size of the network) is also done in this layer.

Hub, Repeater, Modem, Cables are Physical Layer devices. 
Network Layer, Data Link Layer and Physical Layer are also known as Lower Layers or Hardware Layers.

Examples of hardware in the physical layer are network adapters, ethernet, repeaters, networking hubs, etc.