2018 has seen the launch of a major ITU drive to define the requirements of IMT-2020/5G systems as they relate to transport networks, the extremely high-capacity optical networks that form the ‘backbone’ of the ICT ecosystem.
These 5G transport projects have built strong momentum, drawing on the expertise of a wide range of working groups within ITU’s standardization expert group for ‘transport, access and home’, ITU-T Study Group 15.
The baseline for this work was established in February 2018 with the release of an influential ITU Technical Report placing emerging 5G radio requirements in the context of their demands on transport networks.
The second version of this Technical Report was agreed in October 2018. Download the report…
The report takes a transport network view of 3GPP, CPRI and NGMN specifications, capturing ITU-T Study Group 15’s understanding of emerging 5G requirements.
The report has enabled these other bodies to assist ITU-T Study Group 15 in refining this understanding.
“Few people understand both the wireless and wireline worlds,” says the report’s Editor, Stephen Shew, Ciena, Rapporteur for ITU standards work on ‘transport network architectures’ (Q12/15). “This report aims to build common understanding between relevant standards bodies. It is certainly achieving that, helping ITU-T Study Group 15 to build productive dialogue with 3GPP and NGMN.”
“We have come to agreement on certain key aspects of network management-control,” says Shew, referring to ITU-T Study Group 15’s decision to support 3GPP network slices using the logical subsets of transport resources offered by SDN virtual networks.
SDN virtual networks are an already existing construct in ITU-standardized architectures for network management-control, codified by ITU standards such as ITU G.7702 “Architecture for SDN control of transport networks”.
“We are building on a proven construct and this decision was also motivated be the fact that there are a range of applications other than 5G able to benefit from such subsets of logical resources,” says Shew.
Passive Optical Network (PON), Carrier Ethernet and Optical Transport Network (OTN) are among the technologies standardized by ITU-T Study Group 15 with significant potential to support 5G systems.
The new Supplement 66 to G-series ITU standards highlights the requirements of 5G fronthaul in a PON context. Download the Supplement…
5G will demand fronthaul solutions able to support very high bandwidths. Industry also aims to ensure that these solutions are low cost.
“That introduces PON,” says Frank Effenberger, Huawei, Rapporteur for ITU standards work on ‘optical systems for fibre access networks’ (Q2/15). “’PON provides the necessary capacity and is usually the lowest-cost type of optical network.”
“The new Supplement on PON support for 5G fronthaul does a good job of laying out all possible 5G network architectures, considering the eight layers of possible split between functions and the three-tier network we see 3GPP leaning towards,” says Effenberger.
The Supplement has potential to inform updates to the NG-PON2 series of ITU standards as well as next-generation ‘high-speed PON’ projects underway in ITU-T Study Group 15.
“We are looking to standardize PON systems running at 50G per channel,” says Effenberger. “50G is exactly what’s required for 5G fronthaul – that’s what we are seeing the wireless world requesting.”
Upcoming ITU standards for PON systems may address WDM PON with 32 wavelengths each carrying 50G – “that would provide the bandwidth needed for very high peak-rate 5G systems,” says Effenberger.
“We hear about 5G centralizing processing in C-RANs [Cloud Radio Access Networks] as well as applications such as self-driving cars where vehicles will need to communicate with one another with latencies in the milliseconds,” says Effenberger. “This seems to be pulling in the network in two opposite directions. It’s a very interesting architectural challenge.”
The guiding Technical Report (GSTR-TN5G) will continue to evolve in tune with the evolution of ITU-T Study Group 15’s understanding of 5G transport requirements.
The report identifies four 5G RAN deployment scenarios, describing their influence on the classification of fronthaul, midhaul and backhaul in optical transport networks. It outlines 5G requirements on time and frequency synchronization, highlighting required levels of accuracy defined by 3GPP. And it draws attention to the transport network management-control required to support multiservice capabilities and 5G network slicing, particularly in relation to the interaction of 5G network and transport network management systems.
Complete ITU texts for 5G transport:
Work-in-progress ITU texts for 5G transport:
New work launched in October 2018 to support 5G transport:
The international standards developed by ITU-T Study Group 15 detail technical specifications giving shape to global communication infrastructure. The group’s standards define technologies and architectures of optical transport networks enabling long-haul global information exchange; access networks through which subscribers connect; and home networks connecting in-premises devices and interfacing with the outside world.
Learn more about ITU-T Study Group 15 in an ITU interview with the group’s Chairman, Stephen Trowbridge.