GMPLS and common control
From small beginnings MultiProtocol Label Switching (MPLS) has come a long way in ten years. Although there are a considerable number of detractors who believe it costly and challenging to manage, it has now been deployed in just about all carriers around the world in one guise or another (MPLS-TE) as discussed in The rise and maturity of MPLS. Moreover, it is now extending its reach down the stack into the optical transmission world through activities such as T-MPLS covered in PBB-TE / PBT or will it be T-MPLS? (Picture: GMPLS: Architecture and Applications by Adrian Farrel and Igor Bryskin).
In the same way that early SDH standards did not encompass appropriate support for packet based services as discussed in Making SDH, DWDM and packet friendly, initial MPLS standards were firmly focussed on IP networks not for use with optical wavelength or TDM switching.
The promise of MPLS was to bring the benefits of a connection-oriented regime to the inherently connectionless word of IP networks and be able to send traffic along pre-determined paths thus improving performance. This was key for the transmission of real time or isochronous services such as VoIP over IP networks. Labels attached to packets enabled the creation of Label Switched paths (LSPs) which packets would follow through the network. Just as importantly, it was possible to specify the quality of service (QoS) of an LSP thus enabling the prioritisation of traffic based on importance.
It was inevitable that MPLS would be extended to enable it to be applied to the optical world and this is where the IETF's Generalised MPLS (GMPLS) standards comes in. Several early packet and data transmission standards bundled together signalling and data planes in vertical 'stove-pipes' creating services that needed to be managed from top to bottom completely separately from each other.
The main vision of GMPLS was to create a common control plane that could be used across multiple services and layers thus considerably simplifying network management by automating end-to-end provisioning of connections and centrally managing network resources. In essence GMPLS extends MPLS to cover packet, time, wavelength and fibre domains. A GMPLS control plane also lies at the heart of T-MPLS replacing older proprietary optical Operational Support Systems (OSS) supplied by optical equipment manufacturers. GMPLS provides all the capabilities of those older systems and more.
GMPLS is also often referred to as Automatic Switched Transport Network (ASTN) although GMPLS is really the control plane of an ASTN.
GMPLS extends MPLS functionality by creating and provisioning:
GMPLS has extended and enhanced the following aspects of MPLS:
GMPLS has also added:
As GMPLS is used to control highly dissimilar networks operating at different levels in the stack, there are a number of issues it needs to handle in a transparent manner.
GMPLS / ASTN is now well entrenched in the optical telecommunications industry with many, if not most, of the principle optical equipment manufacturers demonstrating compatible systems.
It's easy to see the motivation to create a common control plane (GMPLS was defined under the auspices of the IETF's Common Control and Measurement Plane (ccamp) working group) as it would would considerably reduce the complexity and cost of managing fully converged Next Generation Networks (NGNs). Indeed, it is hard to see how any carrier could implement a real converged network without it.
As discussed in Path Computation Element (PCE): IETF’s hidden jewel converged NGNs will need to compute service paths across multiple networks, across multiple domains and automatically pass service provision at the IP layer down to optical networks such as SDH and ASTN. Again, it is hard to see how this vision can be implemented without a common control plane and GMPLS.
To quote the concluding comment in GMPLS: The Promise of the Next-Generation Optical: Control Plane (IEEE Communiction Magazine July 2005 Vol.43 No.7):