Overview of GMPLS UNI

Definition

GMPLS is developed from MPLS so that it inherits nearly all MPLS features and protocols. GMPLS also extends the definition of MPLS labels and it can be considered as an extension of MPLS in transmission networks. GMPLS provides a unified control plane for the IP layer and transport layer. In this manner, the network architecture is simplified, the network management cost is reduced, and the network performance is optimized.

The GMPLS User-Network Interface (UNI) is defined by IETF as a network connection interface. It is applicable to the overlay model in the GMPLS network structure and it meets the trend in network development.

GMPLS UNI extends MPLS in the following aspects:

Supports multiple network interface types and supports switching of packets, timeslots, wavelengths, and ports.
Supports explicit routes and explicit labels.
Supports bidirectional LSPs.
Separates the control plane from the data plane, supports outband signaling, and prevents a failure in the control plane from affecting the data plane.
Enables fast fault detection in the control plane and supports end-to-end recovery and protection.
Supports service security mechanisms and service policy authentication.
Supports LSP graceful deletion.

Purpose

In an era when IP technologies evolve quickly and data transmission becomes demanding, IP services impose higher requirements on bandwidth of transport networks. Mainstream bandwidth of transport networks has quickly changed from 155 Mbit/s and 622 Mbit/s to 2.5 Gbit/s and 10 Gbit/s, and to 40 Gbit/s and 100 Gbit/s at present. The processing granularity (VC4) of Synchronous Digital Hierarchy (SDH) networks, however, lags behind. In this case, the Dense Wavelength Division Multiplexing (DWDM) technique becomes one of options to construct a transport network. To provide an end-to-end DWDM solution, the issue in the communication between routers and DWDM devices must be addressed in advance.

To be specific, many User-Network Interfaces (UNIs) are statically configured between IP networks and transport networks, but this configuration has many drawbacks:

Transmission channels between IP networks and transport networks need to be configured manually, which is time consuming and increases carriers' network construction cost.
When a fault occurs and both the primary and secondary paths fail, additional configurations are needed to restore services, increasing carriers' network maintenance cost.
Bandwidth cannot be dynamically adjusted because IP networks and transport networks are interconnected based on static configurations. This defect will waste abundant network resources and lead to unnecessary capacity expansion.

The automatic UNI service deployment feature provided by Generalized Multiprotocol Label Switching (GMPLS) properly solves the preceding problems. GMPLS provides packet switching, wavelength switching, time division switching, and spatial switching, supports multiple interconnection models between transmission networks and IP networks, and truly implements an end-to-end solution. GMPLS brings the following benefits:

Simplified network management, intelligent service provisioning, flexible transmission channel setup, and lower operational and maintenance cost
Abundant protection levels, enhanced network robustness based on an effective protection recovery mechanism, and lower operational&maintenance cost
Flexible resource allocation policies, improved network resource usage, and lower pressure on capacity expansion