ol plane of the transport network and it com- municates with the overlay MPLS control plane via the UNI interface. In the peer model, the IP/MPLS layer operates as a full peer of the transport layer. Specifically, the IP routers are able to determine the entire path of the connection, including through the optical devices. A sort of GMPLS overlay model is obtained using ASON terminology by connecting a standard MPLS layer with an ASON transport network via O-UNI interfaces SO that conceptually there is some correspondence between GMPLS and ASON configurations. As in the case of the ASON architecture, the GMPLS control plane is extended to support multiple switching layers. Moreover, also in GMPLS, there is a clear separation between the multilabel control plane (MLCP) and the data plane at each layer of the network SO that at a specific layer they could have a different topology or be supported by different trans- mission media as shown in Figure 8.8. Unlike control signaling in MPLS that following the IP network paradigm is always in-band, the MLCP can manage the GMPLS network out-of-band; hence control signaling need not follow the forwarded data. This implies that the MLCP can continue to function although there is a disruption in the data plane and vice versa and allows for separate control channels to be used for the MLCP. By deploying the MLCP on separate control channels, the other channels are completely dedicated to forwarding data. In GMPLS, the MLCP utilizes routing and signaling protocols to manage all the network functionalities. These protocols are extensions to well-known protocols of the TCP/IP pro- tocol suite. As such, the MLCP implements IPv4 or IPv6 addressing. This also applies to the data plane, but in cases where addressing is not feasible, or convenient, unnum- bered links (i.e., links without network addresses) are supported. MLCP addresses are not required to be globally unique (however global uniqueness is required to allow for remote management). However, addressing in the MLCP is sepa