Networking - The OSI Seven-Layer Model - The Physical Layer

The purpose of the physical layer is to control the process of transferring individual bits from place to place. As such, it defines:

• Physical network structures,
• Mechanical and electrical specifications for using the transmission medium, and
• Bit transmission encoding and timing rules

Various network devices are normally associated with the physical layer:

• Concentrators, hubs, & repeaters (because they don't know about the content of what they relay, only its voltage, frequency, etc.)
• Connectors for transmission media, like taps and T-connectors (because they mechanically connect the transmission media to network devices)
• Modems and codecs (because they translate digital to analog and vice versa, without regard to data content)

The physical layer is responsible for seven processes, each of which is responsible for a series of methods:

1. Connection Types
   • Point-to-point
   • Multipoint
2. Physical Topology
   • Bus
   • Ring
   • Star
   • Mesh
   • Cellular
3. Digital Signaling
   • Current state
     • amplitude-shift keying
     • frequency-shift keying
   • State transition
     • phase-shift keying
4. Analog Signaling
   • Current state
     • amplitude-shift keying
     • frequency-shift keying
   • State transition
     • phase-shift keying
5. Bit Synchronization
   • Asynchronous
   • Synchronous
     • guaranteed state change
     • separate clock signals
     • oversampling
6. Bandwidth Use
   • Broadband
   • Baseband
7. Multiplexing
   • Frequency-division (FDM)
   • Time-division (TDM)
   • Statistical time-division (StatTDM)

Let's move on to layer 2, the Data Link Layer.

Nah, I want to skip around:

• Introduction
• Physical (Layer 1)
• Data Link (Layer 2)
• Network (Layer 3)
• Transport (Layer 4)
• Session (Layer 5)
• Presentation (Layer 6)
• Application (Layer 7)
• Conclusion

Copyright 1999, Marc Elliot Hall, DBA Sensation! Services