The goal of Application-Layer Traffic Optimization (ALTO) is to
provide guidance to applications that have to select one or several
hosts from a set of candidates capable of providing a desired
resource. ALTO is realized by a client-server protocol. Before an
ALTO client can ask for guidance it needs to discover one or more
ALTO servers that can provide suitable guidance.
This document specifies a procedure for third-party ALTO server
discovery, which can be used if the ALTO client is not co-located
with the actual resource consumer, but instead embedded in a third
party such as a peer-to-peer tracker.
Technically, the algorithm specified in this document takes one
IP address and a U-NAPTR Service Parameter (i.e., "ALTO:http" or
"ALTO:https") as parameters. It performs several DNS lookups (for
U-NAPTR and SOA resource records) and returns one or more URI(s) of
information resources related to that IP address.