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WebSphere WebSphere Application Server Network Deployment, Version 6.0.x Operating Systems: AIX, HP-UX, Linux, Solaris, Windows

Publish/subscribe messaging example using remote publication points

When a publishing or subscribing application is remote from its destination, remote publication points are used to manage the flow of messages between the messaging engine where the destination is located, and the messaging engine to which the application is attached.

The following diagram illustrates the use of remote publication points in publish/subscribe messaging. Messages are published to a publication point on ME1, and are routed to publication points on ME2 and ME3 via remote publication points on ME1. The messages are consumed from subscriptions on ME2 and ME3.

Figure 1. Publish/subscribe messaging using remote publication points.The bus contains three messaging engines, ME1, ME2 and ME3. The publishing application is connected to ME1 and the subscribing applications are connected to ME2 and ME3.  ME1 hosts remote publication point s which represent the publication point s hosted by ME2 and ME3.
The sequence of steps involved in remote publish/subscribe messaging is as follows:
  1. The administrator creates a topic space destination on the bus; this creates a publication point on each messaging engine in the bus.
  2. The subscribing applications register subscriptions for a topic on the topic space on their local messaging engines. ME1 is informed that ME2 and ME3 are interested in the topic.
  3. The publishing application, on ME1, publishes a message for that topic and topic space to the bus, for distribution to the publication points on each messaging engine.
  4. The remote publication points on ME1 queue the message for transmission to their respective publication points on ME2 and ME3.
  5. The message is sent to the publication points on ME2 and ME3 as soon as possible. ME1 remembers the existence of the message until both ME2 and ME3 confirm that they have received the message.
  6. The subscribing applications consume the message via their subscriptions on ME2 and ME3.
In the above example the subscribing applications are attached to the same messaging engines that their subscriptions were created on. If a subscribing application has a durable subscription, it is possible for the application to be attached to a different messaging engine than the messaging engine that the subscription was created on. In this case the subscribing application accesses its subscription via a remote subscription on the messaging engine to which the application is attached. In the example below, messages are published to ME1, and are routed to the durable subscription which resides on ME2. The messages are consumed from ME2 via a remote subscription on ME3.
Figure 2. Publish/subscribe messaging using a remote subscriptionThe bus contains three messaging engines, ME1, ME2 and ME3. The publishing application is connected to ME1 and the subscribing applications are connected to ME2 and ME3.  ME1 hosts remote publication point s which represent the publication points hosted by ME2 and ME3. Subscribing application B is connected to ME3 and receives publications from ME1 via a remote subscription on ME2.
In this situation, Subscribing Application B consumes messages from its subscription in the same way as an application consumes remotely from a queue point, as detailed in Point-to-point messaging example using remote queue points.
Related concepts
Point-to-point messaging example using remote queue points
Related tasks
Using durable subscriptions

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Last updated: 5 Oct 2005
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