Introduction to GMPLS

Traditional MPLS is designed to carry Layer 3 IP traffic using established IP-based paths and associating these paths with arbitrarily assigned labels. These labels can be configured explicitly by a network administrator, or can be dynamically assigned by means of a protocol such as LDP or RSVP.

GMPLS generalizes MPLS in that it defines labels for switching varying types of Layer 1, Layer 2, or Layer 3 traffic. GMPLS nodes can have links with one or more of the following switching capabilities:

Label-switched paths (LSPs) must start and end on links with the same switching capability. For example, routers can establish packet-switched LSPs with other routers. The LSPs might be carried over a TDM-switched LSP between SONET add/drop multiplexers (ADMs), which in turn might be carried over a lambda-switched LSP.

The result of this extension of the MPLS protocol is an expansion in the number of devices that can participate in label switching. Lower-layer devices, such as OXCs and SONET ADMs, can now participate in GMPLS signaling and set up paths to transfer data. A router can participate in signaling optical paths across a transport network.

Two service models determine the visibility that a client node (a router, for example) has into the optical core or transport network. The first is through a user-to-network interface (UNI), which is often referred to as the overlay model. The second is known as the peer model. Juniper Networks supports both models.

Note: There is not necessarily a one-to-one correspondence between a physical interface and a GMPLS interface. If a GMPLS connection uses a nonchannelized physical connector, the GMPLS label can use the physical port ID. However, the label for channelized interfaces often is based on a channel or time slot. Consequently, it is best to refer to GMPLS labels as identifiers for a resource on a traffic engineering link.

To establish LSPs, GMPLS uses the following mechanisms:

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