Multiple Access Protocols in Computer Networks

Lecture Outcomes

• Understand the need for multiple access protocols
• Learn about various multiple access protocols

Key Concepts

Analogy

• Classroom scenario: If all students answer simultaneously, chaos ensues.
• Teacher's role: Manage students to answer one at a time.
• In computer networks: If the medium is shared, multiple nodes accessing simultaneously can create issues.

Importance of Multiple Access Protocols

• Dedicated link: Data link control layer is sufficient.
• Shared link: Multiple stations can access the channel simultaneously, leading to collisions.
• Collision: When two or more stations send data simultaneously without checking if the channel is busy or idle, making the data unusable.

Types of Multiple Access Protocols

1. Random Access Protocols

   • Stations can send data at any time, leading to possible collisions.
   • All stations have equal priority.
   • Procedures must be followed to resolve collisions:
     • When to access the medium
     • Actions if the medium is busy
     • Determine success or failure of transmission
     • Handle access conflicts
   • Examples: ALOHA, CSMA (Carrier Sense Multiple Access), CSMA/CD (CSMA with Collision Detection), CSMA/CA (CSMA with Collision Avoidance)

2. Controlled Access Protocols

   • Stations consult one another for the right to send data.
   • Only authorized stations can send data, avoiding collisions.
   • Examples: Reservation, Polling, Token Passing

3. Channelization Protocols

   • The bandwidth of a shared channel is divided in time, frequency, or code.
   • Examples: FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access), CDMA (Code Division Multiple Access)

Summary

• Multiple access protocols are critical for managing shared channels in networks to avoid collisions and ensure efficient communication.
• Three main types: Random Access Protocols, Controlled Access Protocols, and Channelization Protocols.