Skip to main content

Need of multicast and consensus

Short answer

Multicast provides efficient group communication for replicated services, discovery, updates, and events. Consensus is required for agreeing on a single value despite failures, used in mutual exclusion, leader election, atomic commit, and total order multicast.

What is the need of multicast communication and consensus in distributed system, explain in brief.

Need of multicast communication

Multicast sends a message from one process to a group of processes in a single operation. It is needed for:

  • Fault tolerance based on replicated services: a request is sent to all replicas, which all execute it.
  • Finding discovery services in spontaneous networking, e.g. a client multicasts to find printers.
  • Better performance through replicated data: updates are sent to all copies, for example cached or replicated database copies.
  • Propagation of event notifications: news, stock prices, publish-subscribe systems.
  • Efficiency: one send instead of N separate messages saves bandwidth and time. Reliable and ordered (FIFO, causal, total) multicast is needed so that all members see consistent updates.

Need of consensus

Consensus lets processes agree on a single value even if some fail. It is needed for:

  • Mutual exclusion: agreeing who enters the critical section.
  • Leader election: agreeing on the new coordinator or primary.
  • Atomic commit of transactions: all participants commit or all abort.
  • Replicated state machines and total order multicast: agreeing on order of operations so that all replicas remain identical.
  • Group membership and failure decisions, e.g. who has crashed.
  • Agreement in fault-tolerant control systems, e.g. several sensors agreeing on a reading. Without consensus, replicas diverge and the system behaves inconsistently.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Distributed System chapter 6 questions →