Physical Layer defines electrical and mechanical specifications of cables, connectors and signaling options that physically links two nodes on a network. The major functions and services performed by the physical layer are:
- Bit-by-bit or symbol-by-symbol delivery
- Providing a standardized interface to physical transmission media, including
- Mechanical specification of electrical connectors and cables, for example maximum cable length
- Electrical specification of transmission line signal level and impedance
- Radio interface, including electromagnetic spectrum frequency allocation and specification of signal strength, analog bandwidth, etc.
- Specifications for IR over optical fiber or a wireless IR communication link
- Modulation
- Line coding
- Bit synchronization in synchronous serial communication
- Start-stop signaling and flow control in asynchronous serial communication
- Circuit switching
- Multiplexing
- Establishment and termination of circuit switched connections
- Carrier sense and collision detection utilized by some level 2 multiple access protocols
- Equalization filtering, training sequences, pulse shaping and other signal processing of physical signals
- Forward error correction for example bit wise convolution coding
- Bit-interleaving and other channel coding
The physical layer is also concerned with
- Bit rate
- Point-to-point, multipoint or point-to-multipoint line configuration
- Physical network topology, for example bus, ring, mesh or star network
- Serial or parallel communication
- Simplex, half duplex or full duplex transmission mode
- Auto negotiation
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