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Mobile Computing | DAVV Unit 2

MAC Protocols in Wireless Networks:

MAC protocols manage access to the wireless channel in wireless networks. They determine how devices compete for and use the channel to send data efficiently.

Challenges in Wireless Networks:

  • Hidden terminal: Nodes can’t hear each other but can talk to a central point.
  • Exposed terminal: Nodes avoid transmitting due to interference.

Types of MAC Protocols:

1. Fixed Assignment:

  • Allocates specific time slots or frequencies to nodes.
  • Ensures no collisions but can be inefficient if nodes are idle.

2. Random Assignment:

  • Nodes contend for the channel using random access methods.
  • Listens for ongoing transmissions before sending.
  • Backs off for random time if channel is busy.
  • Example: CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance).

3. Reservation-Based:

  • Mixes fixed assignment and random access.
  • Nodes request channel access in a reservation phase.
  • Data transmission phase follows reservation.
  • Example: RTS/CTS (Request-to-Send/Clear-to-Send) in IEEE 802.11.

Choosing the Right MAC Protocol:

  • Depends on network requirements and trade-offs.
  • Efficiency vs. complexity.
  • Consider hidden/exposed terminal issues and overall network performance.