# Channels

## Senders and Receivers

The core functionality of KubeMQ messaging is sending and receiving messages.

**Senders** (publishers) can send one or many messages (stream) to one or many destinations (Channels). Sending a message does not require the set up of any predefined destination.

**Receiver** (subscribers/listeners) can receive messages from one or more senders on the same channel or a wildcards channel. Before a Receiver can receive any messages, a Subscription function is needed to register his interest in receiving messages from a senders designation.

## Format

A channel string can be formed from any UTF-8 characters with the following attributes:

* Case sensitive, FOO and foo are different channel names
* No white spaces allowed
* Cannot be Blank (`"`)
* `.`, `*`, `>` are special characters for token hierarchies.
* Cannot start with `.`
* Can begin with `>` or `*` (for subscription receivers only)
* Unlimited hierarchies

## Hierarchies

Channels names can be separated by the `.` symbol to create messaging stream hierarchies.

One level hierarchy:

`foo`, `USA`, `org` are valid one level hierarchies.

Two-level hierarchies:

`foo.bar`, `USA.NewYork`, `org.department` are valid two-level hierarchies.

N level hierarchies:

`foo.bar.A.B.C.>` is valid n (n=6) level hierarchies.

## Wildcards <a href="#wildcards" id="wildcards"></a>

KubeMQ supports two wildcards, `*` and `>`. Wildcards are used to subscribe to a group of channels’strings.

### Asterisk `*` <a href="#asterisk" id="asterisk"></a>

Matching a single token in any hierarchy

### Greater `>` <a href="#greater" id="greater"></a>

Matching one or more tokens at the tail of a channel

Examples:

Here some cases of channel subscription patterns and which types of messages with channels are accepted and ignored.

| Channel Pattern | Messages Accepted    | Messages Ignored    |   |
| --------------- | -------------------- | ------------------- | - |
| `foo`           | `foo`                | `bar`,`zoo`         |   |
| `foo.*`         | `foo.bar`,`foo.ZOO`  | `foo`,`foo.bar.zoo` |   |
| `foo.>`         | `foo.bar.zoo`        | `foo`               |   |
| `foo.*.*.bar`   | `foo.a.b.bar`        | `foo.bar.zoo`       |   |
| `foo*.>`        | `foo.bar`,foo1.bar\` | `foo\`              |   |
| `>`             | any message          | none                |   |

![](https://2828835384-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M2b9dwAGbMPWty0fPGr%2F-M2cg-nL53EVg5rPnOZB%2F-M2chJX-k5mdWrwRtioC%2Fchannels.png?alt=media\&token=2cb8b32c-f664-4b68-9496-87676025383b)