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New ITU Standards Optimize Transport Networks Support for IMT-2020/5G

15 Maret 2021 - Artikel

ITU News

ITU has standardized a new technology optimizing the metro transport network to support IMT-2020/5G with carrier-class Ethernet. The new transport technology targets the transport of traffic from distributed and centralized radio access networks, providing the full range of operations, administration and management (OAM) capabilities required by carriers.

ITU G.8312 “Interfaces for the metro transport network” adapts IEEE 802.3 Ethernet technology and OIF Flexible Ethernet (FlexE) implementation logic to the requirements of carrier-class transport networks. The OAM capabilities provided by ITU G.8312 include connection verification, performance monitoring, path status, and delay measurement. 

5G transport standardization is led by ITU-T Study Group 15 (Transport, access and home).

The ITU G.8312 interfaces and accompanying ITU G.8310 architecture for the metro transport network build on the success of ITU standards for carrier-class Ethernet, standards that brought carrier-class management and control capabilities to Ethernet technology to support Ethernet’s emergence as the preferred ‘onramp’ to the information superhighways provided by Optical Transport Network (OTN) technology.            

The development of ITU G.8312 and G.8310 received more than 200 technical contributions over a two-year development cycle, “what is probably record number of contributions on a single topic in such a short space of time,” says Steve Gorshe, Microchip Technology, Rapporteur for the responsible working group (Q11/15).

ITU G.8312 defines a new Section layer adapted from FlexE and a new Path layer based on carrying the Ethernet 66B-encoded block streams. ITU G.8312 makes substantial use of existing technology, creating commonality with other portions of the network as well as associated network management systems. “The technology is especially well suited to carriers using Ethernet technology in their radio access networks in need of the capabilities of a carrier-grade transport network,” says Gorshe.

A key extension to OTN technology in ITU G.709.4 “OTU25 and OTU50 short-reach interfaces” is another ITU standard designed to support 5G transport also developed by the Q11/15 working group. Read more about the latest updates to the ITU G.709 series.

ITU G.709.4 defines nominally 25 and 50 Gbit/s OTN interfaces optimized for carrying Ethernet 25GBASE-R and 50GBASE-R client signals.

“These are the rates becoming popular in 5G radio access networks,” says Gorshe. “The ITU G.709.4 interfaces make it much easier for carriers to continue to base their radio access networks on OTN technology.”

An informative appendix to ITU G.709.4 also defines lower-rate OTN interfaces that operate at the same rates as Ethernet 25GBASE-R and 50GBASE-R signals, enabling the use of these OTN interfaces for applications where a network operator desires direct reuse of Ethernet optical modules.

More ITU guidance on 5G transport 

ITU’s Radiocommunication Sector (ITU-R) coordinates the standardization of International Mobile Telecommunications (IMT) and identification of spectrum for mobile development - learn more about IMT-2020/5G. ITU’s Standardization Sector (ITU-T) plays a similar convening role for the technologies and architectures of the wireline elements of 5G systems.

2018 saw 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 drawn on the expertise of a wide range of working groups within 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 took a transport network view of 3GPP, CPRI and NGMN specifications, capturing ITU-T Study Group 15’s understanding of emerging 5G requirements and enabling these other bodies to assist ITU-T Study Group 15 in refining this understanding.

New ITU guidance on 5G transport continues to result.

ITU G.8310 and ITU G.8312 are the latest additions to the new ITU G.8300 series of standards addressing transport aspects of 5G mobile networks. The first standard in the series, ITU G.8300 “Characteristics of transport networks to support IMT-2020/5G” described the relationship of 5G network architecture to transport network architecture, defining fronthaul, midhaul and backhaul and documenting their requirements and characteristics in relation to 5G transport.

3GPP network slices will be supported using the logical subsets of transport resources offered by software-defined networking (SDN), a proven construct codified by ITU standards such as ITU G.7702 “Architecture for SDN control of transport networks”. This decision of ITU-T Study Group 15 was motivated by SDN virtual networks having proved their value and considering the range of other applications other than 5G able to benefit from such subsets of logical resources.

Advances through 3G, 4G and 5G have called for increasing precision in network timing and synchronization. 5G requirements on time and frequency synchronization are addressed by ITU-T G.8273.2/Y.1368.2 "Timing characteristics of telecom boundary clocks and telecom time slave clock" and ITU-T G.8262.1/Y.1362.1 (Amendment 1) "Timing characteristics of an enhanced synchronous equipment slave clock".

Passive Optical Network (PON) systems provide the necessary capacity for 5G fronthaul alongside attractive cost efficiency. ITU G.9804.1 “Higher speed passive optical networks – Requirements” describes the requirements of next-generation PON systems to support line rates of 50 Gbit/s. In addition, ITU G.9802 "Multiple-wavelength passive optical networks (MW-PONs)" provides a foundation for ITU standards to enable WDM PON systems to support several channel-count options at a line rate of 25 Gbit/s per channel.

To overcome the scarcity of fibre facilities in many access networks, ITU also continues to develop bidirectional point-to-point optical access solutions where a single fibre supports both directions of transmission. ITU G.9806 (Amendment 1) “Higher speed bidirectional, single fibre, point-to-point optical access system” supports line rates of 10 Gbit/s and 25 Gbit/s and support for 50 Gbit/s is anticipated for future editions of the standard.

Learn more about ITU-T Study Group 15

The international standards developed by ITU-T Study Group 15 define networks, technologies and infrastructures for transport, access and home.

For all working groups (‘Questions’), see list of Questions and Rapporteurs.

To learn more about ITU-T Study Group 15, contact tsbsg15@itu.int.

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