# Understanding system messages for Amazon Chime SDK messaging
<a name="system-messages"></a>

Amazon Chime SDK sends system messages to all connected clients for events that take place in channels. Events include:
+ `UPDATE_CHANNEL` – This event signifies any update made to the channel details, such as the name or metadata.
+ `DELETE_CHANNEL` – This event signifies that the channel and all of its data, including messages, memberships, moderators and bans, will be deleted.
+ `CREATE_CHANNEL_MEMBERSHIP` – This event signifies that a particular `AppInstanceUser` has been added as a member to the channel. The event also contains details of the new `AppInstanceUser`.
+ `DELETE_CHANNEL_MEMBERSHIP` – This event signifies that an `AppInstanceUser` has been removed from the channel. The event also contains the removed `AppInstanceUser` details.
+ `UPDATE_CHANNEL_MEMBERSHIP` – This event only applies to elastic channels. The event signifies that membership balancing transferred an `AppInstanceUser` from one sub-channel to another. The event also contains the `AppInstanceUser` details, plus the information about the sub-channel that the `AppInstanceUser` was transferred to.