Wikipedia ALE article

Wikipedia has a wealth of information on Automatic Link Establishment (ALE) which is growing in popularity among Radio amateurs.

Automatic Link Establishment, commonly known as ALE, is the worldwide de facto standard for initiating and sustaining HF (High Frequency) radio communications.

ALE is a feature in an HF communications radio transceiver system, that enables the radio station to make contact, or initiate a circuit, between itself and another HF radio station or network of stations. The purpose is to provide a reliable rapid method of calling and connecting during constantly changing HF ionospheric propagation, reception interference, and shared spectrum use of busy or congested HF channels.

For further information on this mode see the Wiki Automatic Link Establishment pages at:
http://en.wikipedia.org/wiki/Automatic_link_establishment

Free Amateur radio ALE software which uses the PC soundcard can be downloaded from
http://hflink.com/software/