WAS v8.5 > WebSphere applications > Messaging resources > Interoperation with WebSphere MQ > Interoperation using a WebSphere MQ link

Request-reply messaging through a WebSphere MQ link

When a JMS producer sends a message, it can provide a reply-to destination. The reply-to destination is a JMS destination defined using the producer's messaging provider. This style of messaging is known as request-reply, or request and response. Request-reply messages can be exchanged across the WebSphere MQ link as either point-to-point or publish/subscribe messages.

The following combinations are possible for request-reply exchanges:

1. Publication messages (for publish/subscribe messaging).
   1. Queue type reply-to destination.
   2. Topic type reply-to destination. This can be a permanent reply-to topic, which is defined to the publish/subscribe bridge on the WebSphere MQ link, or a temporary topic reply, where the topic name is assigned at runtime.

2. Point-to-point messages.
   1. Queue type reply-to destination.
   2. Topic type reply-to destination. The reply-to destination must be a permanent reply-to topic; we cannot have a temporary topic reply for a point-to-point request message.

When the producer is a WAS application that uses the default messaging provider, the reply-to destination is a service integration JMS destination that typically either points to a service integration queue, or comprises a topic string and a service integration topic space.

• If the reply-to destination is a service integration queue, it is normally a queue in the same bus as the WAS application, so the WAS application can consume the reply message from that reply-to queue.

• If the reply-to destination is a topic and the consumer is a WebSphere MQ program, configure the publish/subscribe bridge to ensure the reply message can be routed back to the service integration bus so the WAS application can receive it. Note that although WebSphere MQ JMS applications can reply to a topic, most other WebSphere MQ applications cannot.

When the producer is a WebSphere MQ JMS application, the reply-to destination is a WebSphere MQ JMS destination that typically either points to a WebSphere MQ queue or is a topic string.

• If the reply-to destination is a WebSphere MQ queue, it is normally a queue in the queue manager, or shared queue in the queue-sharing group, the WebSphere MQ application is using, so the WebSphere MQ application can consume the reply message from that reply-to queue.

• If the reply-to destination is a topic and the consumer is a WAS application, configure the publish/subscribe bridge to ensure the reply message can be routed back to WebSphere MQ so the WebSphere MQ application can receive it.

Subtopics

• Reply-to queues for request-reply messaging through a WebSphere MQ link
  Reply-to queues indicate to a receiving application where a reply should be sent. We can use reply-to queues for point-to-point request messages (queues) and for publish/subscribe request messages.
• Reply-to topics for request-reply messaging through a WebSphere MQ link
  WAS and WebSphere MQ JMS applications can publish messages to a topic space with a reply-to topic. Applications in the other network can receive the message, obtain the reply destination, and publish a message on the reply topic. Topic type replies cross the WebSphere MQ link through the publish/subscribe bridge.

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