**11. MPLS, and GMPLS traffic engineering**

Network control (NC) can be classified as centralized or distributed. In centralized network control, the route control and route computation commands are implemented and issued from one place. Each node in the network communicates with a central controller and it is the controller's responsibility to perform routing and signaling on behalf of all other nodes. In a distributed network control, each node maintains partial or full information about the network state and existing connections. Each node is responsible to perform routing and signaling. Therefore, coordination between nodes is required to alleviate the problem of contention.

Since its birth, the Internet (IP network) has employed a distributed NC paradigm. The Internet NC consists of many protocols. The functionality of resource discovery and management, topology discovery, and path computation and selection are the responsibility of routing protocols. Multiprotocol label switching (MPLS) has been proposed by IETF, to

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IETF proposed an extension to the MPLS-TE control plane to support optical layers in optical networks; this extension is called the multiprotocol lambda switching (MPλS) control plane. In an MPLS network, the label-switching router (LSR) uses the label swapping paradigm to transfer a labeled packet from an input port to an output port. In the optical network, the OXC uses switch matrix to switch the data stream (associated with the light path) from an input port to an output port. In both LSR and OXC, a control plane is needed to discover, distribute, and maintain state information and to instantiate and maintain the

The functional building blocks of the MPλS control plane are similar to the standard MPLS-TE control plane. The routing protocol (e.g. OSPF or IS-IS) with optical extensions, is responsible for distributing information about optical network topology, resource availability, and network status. This information is then stored in the TE database. A constrained-based routing function acting as a path selector is used to compute routes for LSPs through mesh network. Signaling protocols (e.g. RSVP-TE or CR-LDP) are then used to

Another extension to the MPLS control plane is proposed to support various types of optical and other switching technologies. This extension is called Generalized Multi-Protocol Label Switching (GMPLS). In the GMPLS architecture, labels in the forwarding plane of Label Switched Routers (LSRs) can route the packet headers, cell boundaries, time slots, wavelengths or physical ports. The following switching technologies are being considered,

**Packet switching:** The forwarding mechanism is based on packet. The networking gear is an

**Layer 2 switching:** The forwarding mechanism is based on cell or frame (Ethernet, ATM,

Fig. 3. MPLS-TE functional components.

connections under various TE roles and policies.

set up and maintain the LSPs by consulting the path selector.

**11.2 MPλS/GMPLS control plane** 

as shown in Figure 3.

and Frame Relay).

IP router.

enhance classic IP with virtual circuit-switching technology in the form of label switched path (LSP). MPLS is well known for its TE capability and its flexible control plane.

Then, IETF proposed an extension to the MPLS-TE control plane to support the optical layer in optical networks; this extension is called the Multiprotocol Lambda Switching (MPλS) control plane. Another extension to MPLS was proposed to support various types of switching technologies. This extension is called Generalized Multi- Protocol Label Switching (GMPLS). GMPLS has been proposed in the Control and Measurement Plane working group in the IETF as a way to extend MPLS to incorporate circuit switching in the time, frequency and space domains.
