Messages sent through PubNub are sent on a “channel.” Any device subscribing to a channel will receive messages in under 250ms, regardless of which PoP the message was published. Devices can subscribe to thousands of channels simultaneously through a single open connection.
A key point to understand about PubNub channels (unlike older messaging system designs) is that PubNub supports an unlimited number of channels. Channels do not have to be defined in advance; they are automatically created by the act of publishing a message onto the channel. This enables interesting design patterns for realtime applications. For example, each device can have its own channel, while also subscribing to a group channel and a global channel where all devices can receive data simultaneously.
Channels are unique for each key set (the publish and subscribe keys). So a channel named ‘blue’ for one pub/sub key set is not the same as a channel by the same name under a different key set. In other words, you cannot publish a message on a channel under one key set and receive that message under another key set (you can think of a key set as a namespace for channels).
Channel and Channel Group names are UTF-8 compatible and are limited to 92 characters in length.