Decentralization

Rendezvous certified message delivery has a decentralized, stream-oriented, peer-to-peer architecture. Table 25 outlines the differences between centralized, server-based architectures (such as message queuing products), and decentralized architectures (such as Rendezvous certified message delivery).

Table 25 Centralized versus Decentralized Architecture (Sheet 1 of 3)
Aspect	Centralized	Decentralized
Example	JMS Message queuing products.	Rendezvous Certified Message Delivery
Components	Message producers. Message consumers. Centralized server as intermediary.	Message producers. Message consumers.
Basic Operating Principle	A producer sends a message to the central server. The server stores the message until it has delivered it to each consumer.	A producer sends a message to consumers. The producer stores the message until each consumer has acknowledged receipt.
Communication Pattern	Producer to server; server to consumers.	Peer-to-peer.
Protocol	Store and forward queue protocol.	Stream-oriented protocol.
Administration	An intermediary server is required between producers and consumers.	No intermediary is required. Producers communicate directly with consumers.
Resources
Network Bandwidth	Each message traverses the network at least twice—once from the producer to the server, and again from the server to the consumers. Some servers multicast to all consumers simultaneously; others send to each consumer individually. Control and protocol messages use additional bandwidth.	Each message traverses the network once from producer to all consumers. Control and protocol messages use additional bandwidth.
Storage Resources	The central server stores all messages and delivery state for all its clients; it requires disk resources in proportion to total throughput volume.	Each producer stores its outbound messages and some delivery state; it requires disk resources in proportion to its outbound volume. Each consumer stores its inbound delivery state; it requires minimal disk resources.
Storage Integrity	Disk failure on a server host computer can be catastrophic, affecting all messages from every client. Many installations protect against disk failure using safeguards such as disk mirroring.	Disk failure on a peer host computer affects only the messages that its programs produce or consume. However, disk mirroring for each individual peer is often impractical.
State
State Information	All information about message delivery state resides with the central server.	Information about message delivery state is distributed, residing in part with each individual producer, and in part with each individual consumer.
State Master	The central server is the master of overall delivery state.	Since delivery state information is distributed, no entity can be the single master of the overall state. Rather, individual peers are masters of their own parts of the state. Relay agents are not masters of any state.
Monitoring Delivery State	Programs can query the state master (server) about delivery state.	Delivery state monitoring requires application-level code in each producer and consumer.
Changing Delivery State	In some centralized architectures, the state master (server) can make administrative changes to delivery state—for example, it might delete, reorder, or replay messages.	No central component can make administrative changes to overall delivery state.

Table 25 Centralized versus Decentralized Architecture (Sheet 1 of 3)

Message queuing products.

Rendezvous Certified Message Delivery

Components

Message producers.

Message consumers.

Centralized server as intermediary.