Reliable versus Certified Message Delivery

Standard Rendezvous communications software features reliable message delivery, which works well for many programs. Certified message delivery protocols offer even stronger assurances of delivery, along with tighter control, greater flexibility and fine-grained reporting. Table 24 compares the two delivery protocols.

Table 24 Comparing Reliable and Certified Message Delivery (Sheet 1 of 2)
Aspect	Reliable Delivery	Certified Delivery
Location of Protocols	Reliable message delivery protocols are implemented in the Rendezvous daemon (rvd).	Certified message delivery protocols are implemented in a separate library layer (tibrvcm). This library uses rvd for message transport.
Protocol Visibility	Reliable delivery protocols are invisible to programmers.	Certified delivery calls automatically adhere to certified delivery protocols, yet the protocols give programmers abundant status information and limited control.
Protocol Information	Rendezvous daemons inform programs when data is lost. Minimal information about the lost data is available.	The library presents advisory messages to inform programs of every significant event related to certified delivery. Advisories identify specific messages by correspondent name, subject name and sequence number.
Ledger	None.	The certified delivery library records outbound messages in a ledger, either within the program process storage, or in file storage.
Data Recovery	rvd retains outbound messages for the duration of the effective reliability interval.	The certified delivery library retains outbound messages in the ledger until either delivery is complete or the time limit (set by the program) expires.
Data Persistence	Until the reliability interval elapses, or until rvd process termination—whichever is first.	With persistent correspondents, certified delivery can extend beyond program process restart. It is not affected by rvd process termination.
Network Bandwidth	Minimal network overhead beyond the message itself.	Additional network overhead to confirm delivery of each certified message.
File Storage	No file storage overhead.	Optional file-based ledgers consume file storage for each message until delivery is complete (or the time limit expires).
Routing Daemons	Both protocols work across Rendezvous routing daemons (rvrd).

Table 24 Comparing Reliable and Certified Message Delivery (Sheet 1 of 2)

Aspect

Reliable Delivery

Certified Delivery

Location of Protocols

Reliable message delivery protocols are implemented in the Rendezvous daemon (rvd).

Certified message delivery protocols are implemented in a separate library layer (tibrvcm). This library uses rvd for message transport.

Protocol Visibility

Reliable delivery protocols are invisible to programmers.

Certified delivery calls automatically adhere to certified delivery protocols, yet the protocols give programmers abundant status information and limited control.

Protocol Information

Rendezvous daemons inform programs when data is lost. Minimal information about the lost data is available.