Channels provide a robust and effective way of distributing dependencies, and are the next advance in distributed development. Channels allow developers of applications to provide a 1-step method of installing diverse packages and other application components with a known directory structure and with full dependency validation
Currently, the only solution to depending on code from several sources is to bundle the code. This has several bad side effects, the most obvious of which is that code size increases dramatically, and makes upgrading for a simple bug fix a complicated download for the user.
Channels allow an application developer to depend on packages from pear.php.net, a package from pear.example.com, and others. The user will only need to install/upgrade from a single source using the pear installer. With the current state of affairs, the pear installer is only really useful for installing, well, PEAR packages. Because of this difficulty (among others), traditionally very few packages are available as PEAR packages that can be installed with the PEAR installer.
PEAR 1.4 aims to eliminate this and other barriers to application development.
Documentation is not yet complete