Techniques used in the ALE standard include automatic signaling, automatic station identification (sounding), polling, message store-and-forward, linking protection and anti-spoofing to prevent hostile denial of service by ending the channel scanning process. Optional ALE functions include polling and the exchange of orderwire commands and messages. The orderwire message, known as AMD (Automatic Message Display), is the most commonly used text transfer method of ALE, and the only universal method that all ALE controllers have in common for displaying text. It is common for vendors to offer extensions to AMD for various non-standard features, although dependency on these extensions undermines interoperability. As in all interoperability scenarios, care should be taken to determine if this is acceptable before using such extensions.