GMPLS (Generalized Multi-protocol Label Switching)
GMPLS is a proposed IETF standard to simplify the creation and management of IP services over optical networks.
The standard, still one to two years from completion, would create a single control plane that extends from IP at Layer 3 right down to the optical transport level at Layer 1.
GMPLS would build on the work of MPLS, which improves IP scalability and quality of service by creating virtual label-switched paths (LSP) across a network of label switching routers (LSR). 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 operates as a full peer of the optical transmission layer. Specifically, the IP routers are able to determine the entire path of the connection, including through the optical devices.
The aim of GMPLS - both peer and overlay models - is to extends the reach of MPLS from routers through to the optical domain, where forwarding decisions are based on time slots, wavelengths or physical ports (called "implicit labels" in GMPLS terminology), not packet boundaries. GMPLS enables such cross-domain peering by supporting new classes of LSRs, including dense wavelength division multiplexers, add/drop multiplexers and optical cross-connects.
The most significant aspect of GMPLS is the way it influences how labels are requested and distributed, bandwidth is allocated and network failures are "communicated.
GMPLS uses Interior Gateway Protocol (IGP) extensions to support various link types - normal, nonpacket and forwarding adjacencies into the link-state database. If nodes at both ends of the link can receive and transmit packets, GMPLS identifies them as a normal link. If not, they become a nonpacket link. If an LSR creates and maintains a label-switched path, it can announce the LSP into the IGP as a forwarding adjacency.
Crucial to this approach is GMPLS defining the hierarchy of LSPs. This lets the nesting of LSPs support the establishment of traffic trunks. The function is similar to MPLS' support for label stacking, in which many smaller LSPs can be aggregated into one larger LSP. GMPLS operates much the same as LSPs operate, which is as a virtual representation of physical paths.
Under the hierarchy GMPLS sets up, LSPs that begin and end with packet-switched nodes are at the bottom, followed in ascending order by those tied to TDM switching nodes, lamba switching nodes and fiber switching nodes.
From GMPLS unifies network layers, Network World Tech Update, 04/28/03.
Additional resources
GMPLS White Papers/Tutorials/Presentations
Links to a large number of GMPLS papers.
Streamlining your network with G-MPLS
Daniel Briere discusses the ramifications of GMPLS for service providers. The Bleeding Edge, 11/12/02.
Streamlining your network with GMPLS - Part 2
More from Briere. The Bleedging Edge, 01/07/03.
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