OSI Model – Physical Layer (Layer 1)

Data Frames from the Data Link Layer are converted to BITS (0’s and 1’s) and are handed to the next layer known as Physical Layer or Layer 1.

Well the name Physical Layer, suggests that it has something to do with the Physical part of the network, which might be Network Interface Card (NIC), the cables (Ethernet Cables, Fiber Optics), etc.

The Physical Layer specifies the electrical, mechanical, procedural and functional requirements for activating, maintaining and deactivating physical link between end systems.

HUB is a Layer 1 device; it is actually a multiport repeater. It receives a digital signal and reamplifies or regenerates that signal, and then forwards the signal out to all active ports.

Physical Layer can be thought of the actual physical path through which data gets transferred.

Most of the network problems unfortunately occur in this Layer, which can be anything from a NIC that has gone bad to the cables connecting devices.

User	Service
Application Layer	Web Browser, Email Clients
Presentation Layer	Formats data, compression, encryption, etc
Session Layer	Maintains dialog control, creating session and controlling session and ending session.
Transport Layer	End-to-end communication
Network Layer	Layer 3 logical addressing and routing
Data Link Layer	Layer 2 Physical Addressing and Framing with error notification.
Physical Layer	Physical Topology

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