ASTN, short for Automatically Switched Transport Network, is a type of network that can automatically manage the signalling and routing of a network. Traditionally, it was necessary to configure cross-connections in the Network Elements (such as an optical switch) to create a new traffic path for a customer. It is necessary to know that though the term ASTN replaces the term ASON (Automatically Switched Optical Network) and is often used interchangeably with GMPLS, it is not completely correct as GMPLS is a family of protocols, but ASON/ASTN is an optical/transport network architecture.
ASTN uses the Generalized MPLS signalling protocol to set up and monitor edge-to-edge transport connections. ASTN concentrates on SDH/SONET rings in the access networks and metropolian area networks, so called city rings. The related ASON focuses on the optical backbone network that connects these city rings. ASTN is defined in ITU Recommendation G.807. This recommendation is previously known as G.ASTN.
In an ASTN, this process can be automated. The customer defines a new path by its start and end point, the bandwidth needed, the Quality of Service and so on. The Network Elements have the necessary processing functions, in the form of an ASTN agent, built in to configure the new traffic path. The path itself is not specified by the customer. The ASTN agents can re-route the traffic path if the network is changed.