Lecture Notes: Data Encoding and Frame Standards

Physical Layer Encoding

• Data is encoded as:
  • Electrical signals for copper cables
  • Light for optical cables
  • Radio waves for wireless
• Data must be interpretable by devices and is organized into frames.

Frame Standards

• Ethernet 2: Used for wired applications
• 802.11: Used for wireless applications
• Older standards have been consolidated into these two due to similar requirements for copper and optical cables.

Data Link Layer

• Provides data delivery across a single hop (device to router).
• Multiple frames are needed for multi-hop journeys in networks.

Ethernet and Wireless Frames

• Ethernet 2: Used for wired connections
  • Easier to handle without different properties like wireless.
• 802.11: Used for wireless connections
  • Deals with issues like signal degradation over distance.

MAC Address

• Definition: Media Access Control address, a unique identifier for networked devices.
• Structure: 48 bits, represented as six pairs of hexadecimal numbers.
• Assignment and Management:
  • Managed by a centralized authority (IANA) that distributes address blocks to vendors.
  • Organizational Unique Identifier (OUI) indicates the vendor.

Frame Components and Functions

• Source and Destination Addresses: Indicate origin and destination of frames.
• Payload: Actual data being transported.
• EtherType: Indicates the protocol of the payload (e.g., IPv4, IPv6).
• CRC (Cyclic Redundancy Check): Ensures data integrity by checking errors.

Ethernet Frame Structure

• Consists of destination and source MACs, EtherType, payload, and CRC.
• May include Preamble and Interframe Gap for connection establishment and frame spacing.

Quality of Service (QoS)

• 802.1Q Header: Supports frame prioritization for real-time sensitive applications.
• Applications that benefit:
  • Streaming video
  • Voice over IP
  • Online gaming

Hubs and Switches

• Hub: Layer 1 device, creates collision domain issues.
  • CSMA/CD used as a temporary solution for collision management.
• Switch: Layer 2 device, smarter forwarding decisions.
  • Learns devices using MAC address table.

Wireless Frames

• Management, Control, and Data Frames
  • Management frames help in connection/disconnection.
  • Control frames assist in data delivery and acknowledgments.
• Hidden Node Problem: A solution to manage wireless collisions through RTS/CTS.

Conclusion

• Data link layer manages the initial delivery of frames in a network.
• The switch and MAC address table are crucial to efficient network traffic management.
• Wireless frames have additional complexity due to the nature of wireless connections.