The premise of multiprotocol label switching (MPLS) is to speed up packet forwarding and provide for traffic engineering in Internet protocol (IP) networks. To accomplish this, the connectionless operation of IP networks becomes more like a connection-oriented network where the path between the source and the destination is precalculated based on user specifics. To speed up the forwarding scheme, an MPLS device uses labels rather than address matching to determine the next hop for a received packet. To provide traffic engineering, tables are used that represent the levels of quality of service (QoS) that the network can support. The tables and the labels are used together to establish an end-to-end path called a label switched path (LSP). Traditional IP routing protocols (e.g., open shortest path first [OSPF] and intermediate system to intermediate system [IS–IS]) and extensions to existing signaling protocols (e.g., resource reservation protocol [RSVP] and constraint-based routing–label distribution protocol [CR–LDP]) comprise the suite of MPLS protocols.

Generalized MPLS (GMPLS) extends MPLS to provide the control plane (signaling and routing) for devices that switch in any of these domains: packet, time, wavelength, and fiber. This common control plane promises to simplify network operation and management by automating end-to-end provisioning of connections, managing network resources, and providing the level of QoS that is expected in the new, sophisticated applications.

This tutorial focuses on the issues that GMPLS resolves in providing a common control plane to operate across dissimilar network types (e.g., packet, time division multiplexing [TDM], and optical). Initially, a brief overview of MPLS and its evolution to GMPLS is given. Next, a summary of GMPLS protocols and important extensions is presented. In-depth coverage of the issues is then provided. At the end, some of the current outstanding issues in GMPLS are explored.