Introduction to the Request-Reply Communication Pattern

This chapter describes the Request-Reply communication pattern, which is available with the Connext DDS Professional, Evaluation, and Basic package types.

The fundamental communication pattern provided by Connext DDS is known as DDS data-centric publish-subscribe. The data-centric publish-subscribe pattern is particularly well-suited in situations where the same data must flow from one producer to many consumers, or when data is streaming continuously from producers to consumers. For example, the values produced by a temperature sensor may be observed by multiple applications, such as control applications, UI applications, supervisory applications, historians, etc.

Figure 1 Publish-Subscribe Overview

Sending temperature updates using the publish-subscribe pattern

The publish-subscribe pattern supports multicast, which allows efficient distribution from a single source to multiple applications, devices, or subscribers simultaneously. But even with a single subscriber, the publish-subscribe pattern is still advantageous, because the publisher can push new updates to a subscriber as soon as they happen. That way the subscriber always has access to the latest data, with minimum delays, and without incurring the overhead of periodically polling what may be stale data. This efficient, low-latency access to the most current information is important for real-time applications.

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