Channel Basics
A channel is a mechanism through which the data is transmitted from one device to another within the PubNub Real-time Communication Platform. Any device listening to a channel will receive all messages in about 100ms regardless of their location in the world. Most PubNub APIs involve channels as one of the parameters including: sending, receiving, retrieving, securing, deleting, augmenting, and more.
Channel Creation
You don't have to define or create channels in advance as it's done automatically by the act of publishing a message on the channel. When a message is published to a particular channel for the first time, the channel is created.
Channel Limits
There is no limit to the number of channels or the number of users in a channel you can have. A device can listen to thousands of channels simultaneously through a single open connection.
Channel Types
Channels represent any place where messages are sent and received. For example, a channel meant for 1-to-1 direct chat simply means that there are only two users using that channel. A group channel means there are two or more users using that channel.
Here are some useful channel configurations:
Direct channels for one-to-one messaging between two users. You can make these channels private to keep the messages secure between the users.
Group channels for many-to-many messaging between multiple users. For instance, a chat room for your family, or for a group of friends. You can make these channels made public to allow anyone to join, or make them private and only allow select users to join them.
Broadcast channels for announcements, polls, and other situations in which you want to broadcast messages in a one-to-many arrangement.
Unicast channels for poll responses, sensor inputs, location data, and other situations in which you want to aggregate messages in a many-to-one arrangement.
Channel groups allow you to bundle thousands of channels into a group that can be identified by name. When you subscribe to a channel group, you receive data from all the channels the channel group contains.
Channel Names
A channel name can be any alphanumeric string up to 92 UTF-8 characters. Channel names are unique per PubNub key set, and you can have the same name in another key, even within the same PubNub account. In other words, a PubNub key set is a namespace for your channels.
Invalid Characters
, : * / \ and Unicode Zero, whitespace, and non-printable ASCII characters.
Valid Characters
_ - = @ . ! $ # % & ^ ;
A period (.) is valid, however it's a special character that's used for wildcard features and is encouraged to be used strategically to leverage wildcard channel subscribe and Function wildcard channel binding.
Naming Conventions
When it comes to naming your channels, we recommend that you provide a prefix that identifies the purpose of the channel or the types of messages that will be sent over those types of channels.
Following that prefix with a . character further enhances the usefulness of the channel name concerning the wildcard features with several PubNub features, like wildcard subscribe, wildcard channel function binding, and advanced Presence configuration.
For further details on channel naming recommendations, refer to Channel Naming Conventions.
Securing Channels
You can secure your channels by controlling the access to them using PubNub's Access Manager which we will discuss in Access Control in the Security section. With Access Manager disabled, any client can send and receive messages on any channel. This is fine while you're learning to use PubNub but eventually, you'll need to secure your channels.