Message channels

Message channels are the channels that carry messages from one queue manager to another.

Do not confuse message channels with MQI channels. There are two types of MQI channel, server-connection and client-connection. These are discussed in WebSphere MQ Clients.

The definition of each end of a message channel can be one of the following types:

A message channel is defined using one of these types defined at one end, and a compatible type at the other end. Possible combinations are:

Detailed instructions for creating a sender-receiver channel are included in the Quick Beginnings book for your platform (not applicable to z/OS). Examples of the parameters needed to set up sender-receiver channels can be found in this book, in the Example Configuration chapter applicable to your platform. For the parameters needed to define a channel of any type, see the DEFINE CHANNEL command in WebSphere MQ Script (MQSC) Command Reference.

Sender-receiver channels

A sender in one system starts the channel so that it can send messages to the other system. The sender requests the receiver at the other end of the channel to start. The sender sends messages from its transmission queue to the receiver. The receiver puts the messages on the destination queue. Figure 5 illustrates this.

Figure 5. A sender-receiver channel
Messages are sent from the transmission queue at the sender end, to destination queues at the receiver end.

Requester-server channel

A requester in one system starts the channel so that it can receive messages from the other system. The requester requests the server at the other end of the channel to start. The server sends messages to the requester from the transmission queue defined in its channel definition.

A server channel can also initiate the communication and send messages to a requester, but this applies only to fully qualified servers, that is server channels that have the connection name of the partner specified in the channel definition. A fully qualified server can either be started by a requester, or can initiate a communication with a requester.

Figure 6. A requester-server channel
Messages are sent from the transmission queue at the server end to the destination queues defined in the channel definition at the requester end, The channel is usually initiated by the requester, which requests the server end to start. However,a fully-qualified server, defined in the text before the figure, can itself initiate the channel.

Requester-sender channel

The requester starts the channel and the sender terminates the call. The sender then restarts the communication according to information in its channel definition (this is known as callback). It sends messages from the transmission queue to the requester.

Figure 7. A requester-sender channel
The requester starts the channel. The sender ends the call, and restarts the communication according to information in its channel definition. Messages are sent from the sender's transmission queue to and put on the destination queues at the requester end.

Server-receiver channel

This is similar to sender-receiver but applies only to fully qualified servers, that is server channels that have the connection name of the partner specified in the channel definition. Channel startup must be initiated at the server end of the link. The illustration of this is similar to the illustration in Figure 5.

Cluster-sender channels

In a cluster, each queue manager has a cluster-sender channel on which it can send cluster information to one of the full repository queue managers. Queue managers can also send messages to other queue managers on cluster-sender channels.

Figure 8. A cluster-sender channel
A cluster-sender channel is defined from one queue manager to another within the cluster. Messages can be sent from the cluster transmission queue at the sender end to destination queues at the cluster-receiver end.

Cluster-receiver channels

In a cluster, each queue manager has a cluster-receiver channel on which it can receive messages and information about the cluster. The illustration of this is similar to the illustration in Figure 8.