**11.2 MPλS/GMPLS control plane**

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 connections under various TE roles and policies.

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

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, as shown in Figure 3.

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

**Layer 2 switching:** The forwarding mechanism is based on cell or frame (Ethernet, ATM, and Frame Relay).

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2. **Path preemption:** Some tunnels are more important than others. Say for example, a VoIP tunnel and data tunnel may compete for same resources, in which case VoIP tunnel is given a higher priority and data tunnel is made to recalculate a path or just drop, if no path is available. Tunnels have 2 priorities: setup priority and hold priority. Each can have a value from 0 to 7 and the higher the priority numbers the lower the tunnels importance. The setup priority is used when setting up a tunnel and is compared with the hold priority of already established ones. If the setup priority is higher than the hold priority of established tunnel, then established tunnel is

3. **Fast Re-route:** In case of a link failure, interior gateway protocols may take of the order of 10 seconds to converge. Fast reroute involves pre-signaling of backup path along with the primary path. The protection may be path protection (end-to-end) or local protection which may be further differentiated into link protection and node

Fast reroute is a Multiprotocol Label Switching (MPLS) resiliency technology to provide fast traffic recovery upon link or router failures for mission critical services. Upon any single link or node failures, it could be able to recover impacted traffic flows in the level

1. **Link protection:** a link protection model each link (or subset links) used by an LSP is

2. **Node protection:** In a node protection model each node (or subset of nodes) used by an

routing and/or facilitating traffic engineering.

preempted.

protection.

of 50 ms.

Backup path can be configured for:

Fig. 5. Link Protection V/s Node Protection

provided protection by pre-established backup paths.

LSP is provided protection by pre-established backup paths.

Explicit routing may be useful for a number of purposes such as allowing policy

**Time-division multiplexing (time slot switching):** The forwarding mechanism is based on the time frames with several slots and data is encapsulated into the time slots (e.g. SONET/SDH).

**Lambda switching:** λ switching is performed by OXCs.

**Fiber switching:** Here the switching granularity is a fiber. The networkings gears are fiber switch capable OXCs.

Fig. 4. GMPLS Label – Stacking Hierarchy.

The difference between MPλS and GMPLS is that the MPλS control plane focuses on Lambda switching, while GMPLS includes almost the full range of networking technologies.
