A new ITU standard – ITU G.7702 “Architecture for SDN control of transport networks” – describes a hierarchy of software-defined networking (SDN) controllers, providing network operators with vocabulary to specify the functions required by network management systems. The standard is expected to make a key contribution to transport networks’ support for 5G network slicing.
SDN separates network control from the hardware that transfers information. It has strong ties to the open-source movement, first defined in 2012 by the Open Networking Foundation. The concept has since become central to the evolution of the telecoms industry. SDN is a promising a route towards more dynamic network management-control, enabling operators to establish and manage-control virtual network resources without introducing new specialized hardware.
ITU G.7702 was developed by the ITU expert group for ‘transport, access and home’ – ITU-T Study Group 15 – with the aim of assisting network operators in scaling their SDN control systems.
More flexibility, less OPEX
“From an operator’s perspective, SDN is seen as an approach to reduce the OPEX of their network management of multiple vendors,” says Ciena’s Stephen Shew, Rapporteur for ITU-T Study Group 15’s work stream on transport network architectures (Q12/15).
SDN is a flexible, cost-efficient means of accommodating large fluctuations in bandwidth use. It offers an alternative to the overprovisioning of dedicated transport resources, introducing greater cost efficiency with the use of general-purpose ‘white-box’ hardware.
“Prior to SDN approaches, an operator would maybe have a primary and a secondary vendor and somewhat independent management systems which were specific to those equipment,” says Shew. “The SDN approach held the promise of opening up the interfaces downward and also between management systems to enable multiple vendors’ equipment to be managed together.”
The SDN work of ITU-T Study Group 15 is a natural progression of the group’s work on operation support systems (OSS) and automatically switched optical networks (ASON). Transport network technologies developed by ITU-T Study Group 15 are deployed in layers that support one another. Ethernet, for example, can be supported by optical transport networking (OTN), which in turn is supported by wavelength-division multiplexing (WDM). As described in ITU G.7702, SDN controllers can be arranged to mirror this layering for the purpose of management and control.
The ITU G.7702 architecture follows ITU G.7701 “Common Control Aspects”, a standard describing control functions common to SDN and ASON network management-control. ITU G.7701 provides the components of the architecture described by ITU G.7702. “G.7701 is piece parts for the G.7702 architecture and can be piece parts for an evolved ASON or distributed control plane as well,” says Shew.
SDN is key to 5G network slicing
G.7702 gives operators “nomenclature to be able to describe how they want their control systems to interact,” says Shew. “The architecture gives operators a way to understand how they will scale their systems.”
This understanding will support operators in meeting the demands of 5G systems. Industry players have high expectations for SDN and many believe that it will live up to these expectations in the 5G environment.
The deployment of 5G systems will introduce complex traffic-engineering challenges. SDN is expected to assist operators in managing massive changes in bandwidth densities and providing the specialized virtual network ‘slices’ required to meet the needs of different 5G use cases.
“We will be leaning heavily on G.7702 in our work on management to support multiservice capabilities and 5G network slicing,” says Shew.
ITU-T Study Group 15 is accelerating its work on 5G optical transport. The group has published an ITU-T Technical Report placing emerging 5G radio requirements in the context of their demands on the transport network. The report takes a transport network view of 3GPP and CPRI specifications, forming a baseline document to give direction to new ITU-T Study Group 15 standards projects aimed at evolving the transport network in support of 5G.
Download the Technical Report free of charge: GSTR-TN5G “Transport network support of IMT-2020/5G“