 to the maximum number of wavelengths supported at the lowest bit rate on the wavelength, and m indicates the bit rate supported on the interface. Together, these are written as OTM n.m. The OTN supports optical signals with three bit rates: When m equals 1, it refers to 2.5Gbps; when it is 2, it refers to 10Gbps; and when it is 3, it refers to 40Gbps. An interface can support combinations of these rates. For example, OTM 3.2 indicates a channel that spans three wavelengths, each operating at least at 10Gbps. OTM 5.12 indicates a channel that spans five wavelengths and can operate at either Gbps or 10Gbps. ASON and ASTN The OTN differs from today's networks in the types of services it can offer. Instant provisioning requires a signaling protocol to set up the paths or connections SO The Optical Core: Overlay Versus Peer-to-Peer Networking Models that data can be transported. Work on SDH/SONET and OTN signaling is being defined in two ITU ANSI specifications: Automatic Switched Optical Network (ASON)-ITU G.8080 describes ASON, the set of control plane components used to manipulate transport network resources in order to provide the functionality of setting up, main- taining, and releasing connections. ASON is described further later in this chapter, at the end of the section "The IP+Optical Control Plane." Automatic Switched Transport Network (ASTN)-ITU G.807 describes ASTN, which allows traffic paths to be set up automatically through a switched network. ASTN is often used interchangeably with GMPLS. ASTN allows the user to specify the start point, endpoint, and bandwidth required. ASTN/GMPLS consists of several protocols, including routing protocols (OSPF-TE or IS-IS-TE), Link Management Protocol (LMP), and reserva- tion/label distribution protocols (RSVP-TE and CR-LDP). ASTN consists of clients, with each level seeing a differing degree of network detail. Clients can be multiplexers or WDM systems, as well as Ethernet switches or other devices that implement Generic Framing Procedure (GFP), a unifying data link