Preparing channels
Before trying to start a message channel or MQI channel, you must prepare the channel. You must make sure that all the attributes of the local and remote channel definitions are correct and compatible.
Channel attributes describes the channel definitions and attributes.
Although you set up explicit channel definitions, the channel negotiations carried out when a channel starts, might override one or other of the values defined. This behavior is normal, and not apparent to the user, and has been arranged in this way so that otherwise incompatible definitions can work together.
Auto-definition of receiver and server-connection channels
- The appropriate model channel definition, SYSTEM.AUTO.RECEIVER, or SYSTEM.AUTO.SVRCONN. The model channel definitions for auto-definition are the same as the system defaults, SYSTEM.DEF.RECEIVER, and SYSTEM.DEF.SVRCONN, except for the description field, which is "Auto-defined by" followed by 49 blanks. The systems administrator can choose to change any part of the supplied model channel definitions.
- Information from the partner system. The values from the partner are used for the channel name and the sequence number wrap value.
- A channel exit program, which you can use to alter the values created by the auto-definition. See Channel auto-definition exit program.
The description is then checked to determine whether it has been altered by an auto-definition exit or because the model definition has been changed. If the first 44 characters are still "Auto-defined by" followed by 29 blanks, the queue manager name is added. If the final 20 characters are still all blanks the local time and date are added.
When the definition has been created and stored the channel start proceeds as though the definition had always existed. The batch size, transmission size, and message size are negotiated with the partner.
Defining other objects
Before a message channel can be started, both ends must be defined (or enabled for auto-definition) at their queue managers. The transmission queue it is to serve must be defined to the queue manager at the sending end. The communication link must be defined and available. It might be necessary for you to prepare other IBM MQ objects, such as remote queue definitions, queue manager alias definitions, and reply-to queue alias definitions, to implement the scenarios described in Configuring distributed queuing.
For information about defining MQI channels, see Defining MQI channels.
Multiple message channels per transmission queue
It is possible to define more than one channel per transmission queue, but only one of these channels can be active at any one time. Consider this option for the provision of alternative routes between queue managers for traffic balancing and link failure corrective action. A transmission queue cannot be used by another channel if the previous channel to use it terminated leaving a batch of messages in-doubt at the sending end. For more information, see In-doubt channels.
Starting a channel
- Started by an operator (not receiver, cluster-receiver, or server-connection channels).
- Triggered from the transmission queue. This method applies to sender channels and fully qualified server channels (those channels which specify a CONNAME) only. You must prepare the necessary objects for triggering channels.
- Started from an application program (not receiver, cluster-receiver, or server-connection channels).
- Started remotely from the network by a sender, cluster-sender, requester, server, or client-connection channel. Receiver, cluster-receiver, and possibly server and requester channel transmissions, are started this way; so are server-connection channels. The channels themselves must already be started (that is, enabled).