OSI Model: Layers 1 and 2

OSI Model: Layers 1 and 2

• The presentation covers the Physical and Data Link layers of the OSI model.
• The objective is to understand the role of these layers, different transmission media, and MAC addressing in switching.

Physical Layer

• The Physical Layer is responsible for transmitting data over a physical network.
• It defines the physical specifications of cabling, connectors, and electrical signals used for data transmission.
• It manages electrical, optical, or radio signal characteristics.
• Key elements of the physical structure include coax, fiber, wireless, hubs, and repeaters
• Data transmission occurs as a bitstream.
• Sending cable transmits signals.
• Receiving cable receives transmitted signals.

Data Link Layer

• The Data Link layer ensures communication between adjacent nodes.
• It manages data encapsulation in frames, error control, and media access.
• Underlay components include the Logical Link Control (LLC) and Media Access Control (MAC).
• LLC manages flow control and error correction.
• MAC manages access to the transmission medium and MAC addressing.
• Key equipment includes network cards and switches.
• Data Link Layer frames use Ethernet, PPP, switches, and bridges.

Transmission Media

• Transmission media are the means to carry a signal from its origin to its destination.
• There are two categories: wired and wireless.
• Wired media includes coaxial cables, twisted pair cables, and optical fibers.
• Wireless media use electromagnetic waves, infrared, and laser beams.

Cable Media: Coaxial Cable

• Coaxial cables are used in local networks and telecommunications.
• They consist of a conductive inner wire, an insulator, and a conductive outer shield.
• Coaxial cables support analog and digital signals.
• Examples include 10BASE5 and 10BASE2 (older standards).

Wired Media: Twisted Pair Cables

• Twisted pair cables, commonly used in LANs, consist of eight wires in pairs.
• Twisting reduces interference.
• Cables utilize RJ45 connectors.

Twisted Pair Cables: Category and Shielding

• Categories of twisted pair cabling (e.g., Cat5e, Cat6, Cat7, Cat8) are classified based on speed and bandwidth.
• Different types of shielding exist (e.g., UTP, FTP, STP, SFTP).
• Categories determine performance standards (ISO/IEC).

Twisted Pair Cables: Crimping

• Crimping joins the connector to the cable end.
• Standards ensure proper connections.
• Color-coded wires are used for different functions (Transmission, Reception).

Cable Media: Fiber Optics

• Single-mode fiber transmits a single wavelength of light over long distances.
• Multimode fiber transmits multiple wavelengths of light over shorter distances.
• It utilizes light pulses for data transmission, less susceptible to interference.
• Fiber optic cables consist of a core, cladding, and coating.

Wireless Media

• Wireless technologies use electromagnetic waves as their medium.
• Bits are transmitted via modulation techniques.
• Wireless technology uses antennas built into devices or cards.
• Wireless signals attenuate with distance and are affected by walls or obstructions.
• Compared to cables, wireless signals have a limited reach.

Role of Switches

• Switches connect network devices within a single LAN.
• They transfer data frames based on destination MAC addresses.
• They support various communication types: unicast, multicast, and broadcast.

MAC Addressing and Switching

• Every device on a network has a unique MAC address.
• The first three bytes indicate the manufacturer (OUI).
• MAC addresses are used by switches to direct data traffic.
• Switches consult their MAC address table to determine the port for the intended destination.
• Flooding is used when the destination MAC address is not in the table.

Conclusion

• The Physical layer transmits bits over physical media.
• The Data Link layer encapsulates frames and manages MAC addressing.
• Switches are crucial for frame transmission based on MAC addresses.