Distributed group messenger

Group messenger in large-scale distributed systems.

Messages Ordering

Fifo ordering

The message delivery order at each process should preserve the message sending order from every process. But each process can deliver in a different order.

For example:

• P1: m0, m1, m2

• P2: m3, m4, m5

• P3: m6, m7, m8

One of the FIFO ordering would be:

• P1: m0, m3, m6, m1, m2, m4, m7, m5, m8

• P2: m3, m0, m1, m4, m6, m7, m5, m2, m8

• P3: m6, m7, m8, m0, m1, m2, m3, m4, m5

Total ordering

Every process delivers all messages in the same order. Here we don't care about any causal relationship of messages and as long as every process follows a single order we are fine.

For example:

• P1: m0, m1, m2

• P2: m3, m4, m5

• P3: m6, m7, m8

One of the TOTAL ordering would be:

• P1: m8, m1, m2, m4, m3, m5, m6, m0, m7

• P2: m8, m1, m2, m4, m3, m5, m6, m0, m7

• P3: m8, m1, m2, m4, m3, m5, m6, m0, m7

Implmentation of total ordering

• Sequencer: depend on centralized node
• ISIS: distributed algorithm

Network protocol between nodes

• UDP or TCP
• Software multicast