[1Day-1CS] Half-duplex communication (2), wireless communication and Ethernet frames

Types of half-duplex communication

• CSMA/CD: Sends data and retransmits after a period of time if a collision occurs.

• CSMA/CA: Avoids collisions as much as possible by proactively detecting carriers before sending data, etc.

  • Checking the wireless medium before sending data

  • Determining if the line is empty (carrier detection)

  • If busy, checks for availability at increasing intervals based on random values (IFS)

Wireless Communications

• Wifi: Technology that allows electronic devices to connect to a wireless LAN signal; requires a wireless access device.

• BSS (Basic Service Set)

  • Standing for Basic Service Set

  • Simple access through a router + APs and devices within the same BSS can communicate with each other

• Extended Service Set (ESS)

  • One or more connected BSS groups

  • Provides long-range wireless communication

  • Enables more availability and mobility than BSS

  • Allows you to move from one location to another and stay connected to the network without interruption

Ethernet frames

A transport mechanism used at the data link layer

• Preamble: announces the start of an Ethernet frame

• SFD (Start Frame Delimiter): Signals that the MAC address field begins with the next byte.

• DMAC, SMAC: Transmit and receive MAC addresses

• EtherType: defines the IP protocol

• Payload: Data received

• CRC: Error checking bits