ither statically or dynamically according to the actual bandwidth needed between the media gateways. For dynamic set-up there is a need for signalling. In GMPLS the signalling is provided by the protocols RSVP-TE and/or CR-LDP (CR = constraint-based routing). Not all types of traffic carried through the network require the use of LSP paths. For real-time applications and signalling the use of LSPs enables proper service provision, while for non real-time traffic e.g. best effort, the use of LSPs may be omitted to enable more flexibility and reduce the network management costs. MPLS trunks are used to apply adequate traffic engineering, security and resource management on the core network. 12.11 MULTI-LAYER CONTROL 12.11.1 GENERALIZED MPLS, GMPLS As the requirements for bandwidth increase there is a need to manage and control large optical networks. MPLS-based control intelligence is being adopted for use within optical networks to shorten provisioning times. Packet Backbone Ordinary MPLS does not embrace the optical layer. In fact, of the capabilities in Figure 12.7 only the packet-switching capability is included. However, the development pushes a need for a control and management plane that extends from IP at layer 3 right down to the optical transport level at layer 1. This includes fibre-switching capability, lambda light-wave (wavelength) switching capability, time-division multiplexing, and packet-switching capability. The developing standard generalized multi-protocol label switching (GMPLS) aims to meet this need to coordinate capabilities at different layers. GMPLS' primary enhancement to MPLS is its capability to establish connections at layer 1. GMPLS can be deployed in two ways: overlay model or peer model. In an overlay model, also called a UNI, the router is a client to the optical domain and interacts only with the directly adjacent optical node. In the overlay model, the actual physical light path is decided by the optical network and not by the router. In the peer model, the IP/MPLS layer operate