Deploying and Managing Apama Applications > Using Universal Messaging in Apama Applications > Overview of using UM in Apama applications > Comparison of Apama channels and UM channels
Comparison of Apama channels and UM channels
In an Apama application configured to use UM, when an event is sent and a channel name is specified the default behavior is that Apama determines whether there is a UM channel with that name. If there is then Apama uses the UM message bus and the specified UM channel to deliver the event to any subscribers. Subscribed contexts can be in either the originating correlator or other correlators connected to the UM broker.
If a UM channel with the specified name does not exist then the default is that the channel is an Apama channel. An event sent on an Apama channel is delivered to any contexts that are subscribed to that channel.
Regardless of whether the channel is a UM channel or an Apama channel, events are delivered directly to receivers that are connected directly to the correlator.
See Enabling automatic creation of UM channels to learn about how you can change the default behavior.
The following table compares the behavior of Apama channels and UM channels.
Apama channels
UM channels
Configuration of multiple point-to-point connections.
Each execution of engine_connect specifies the correlator to connect to. Each adapter configuration specifies each correlator that adapter connects to.
Correlators and adapters require explicitly set connections to communicate with each other.
Specification of the same UM realm address or addresses.
Startup options for connected correlators specify the same UM realm to connect to. Each adapter configuration specifies the same address for connecting to UM.
Correlators and adapters automatically connect to UM to communicate with each other.
Configuration changes are required when an Apama component is moved to a different host.
No configuration change needed when an Apama component is moved to a different host if both hosts are connected to the same UM realm.
Outside a correlator, channel subscriptions can be from only explicitly connected Apama components.
Outside a correlator, channel subscriptions can be from any Apama component connected to the same UM realm.
Events sent on an Apama channel go directly to subscribers.
Events sent on a UM channel go to the UM broker and then to subscribers.
Connection configurations must be synchronized with application code.
Connection to a UM realm is independent of application code.
Less efficient for sending the same event to many Apama components.
More efficient for sending the same event to many Apama components.
More efficient when sending an event to a context in the same correlator. The event stays inside the correlator.
Less efficient when sending an event to a context in the same correlator. The event leaves the correlator, enters the UM realm, and then returns to the correlator.
Default channel, the empty string, is allowed.
No default channel.
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