ITU-T SG15: G.mtn Metro Transport Network + Transport Support for IMT2020/5G Networks

ZTE and China Mobile report that standardization work for a multi company January 2018 contribution on Slicing Packet Network (SPN) technology was approved as a future ITU-T recommendation for “Metro Transport Networks” (G.mtn) at the October 8-19, 2018 ITU-T SG15 meeting in Geneva.

ITU-T SG15 Q11 focused much of the October meeting on topics related to IMT2020/5G transport networks, and approved three new work items including two related to that area.  The new IMT-2020/5G Transport-related work items are both targeted at metro networks, including transport of RAN traffic.  They are G.mtn “Interfaces for a metro transport network,” which is a new transport technology, and G.709.25-50 “25G and 50G OTN interfaces” that is an extension to the OTN.  The other new work item is G.Sup.sub1G “Sub 1 Gbit/s services transport over OTN” that describes existing and new mappings for sub-Gbit/s clients over OTN.

SPN is a multi-service network platform that can meet new requirements of the 5G transport, data center interconnection, enterprise customer services, residential access network services.  The SPN technology endeavors to provide: low latency, high bandwidth, ultra-high-precision synchronization, flexible management and control, and low cost.

From a January 2018 multi-company SG15 contribution #C678-R1:
SPN considerations for new generation transport network 5G transport and data center interconnection have many new requirements on transport network in many aspects, such as bandwidth, latency, network slicing, control, management, synchronization.
To fulfill these new requirements, the following notes should be considered:
1) Packet Friendly:Packet friendly architecture to share the IP/Ethernet ecosystem, friendly support mainstream packet clients.
2) Leverage Ethernet economic feasibility: Share the economically feasible common component (optical module, technologies and chipsets) ecosystem of 802.3 Ethernet Framer/PHYs.
3) High BW scalability with multiple Ethernet PHY/WDM lambda λ bonding: Support high BW/throughput based on economically feasible Ethernet PHY/interface, including flexible and robust BW scalability with tools such as MLG multi-lane or FlexE multi-PHY bonding mechanism.
4) Simple switching mechanism to achieve low latency and low delay variation of end-to-end service: Support deterministic low latency cross connect of Packet/Data units encoded 64/66b block stream as a mechanism for efficiently grooming time sensitive traffics without the complexity of reading the label/address per packet, without packet buffer queuing, without massive forwarding table lookup, and etc., Moreover, unnecessary heavy wrapping overhead and complex map/demap process should be avoided.
5) Slicing Ethernet Cross Connect, Nested Hard isolation Slicing: Support nested network slicing as a key enabler for network slicing as a service and network slicing wholesaling.
6) Support Multi service: Appropriate Multi service support should be considered. The network should support all kinds of services in Metro network such as Wireless backhaul, Enterprise e-Line/e-LAN, residential broadband.
7) High accuracy timing synchronization: High accuracy timing synchronization better than +/- 130ns for 5G wireless. The synchronization aspect is currently under discussion and development in Q13, this contribution will not discuss it in any detail on this aspect.
8) Flexible and smart control/management mechanism: SDN is a useful tool to simplify the network, equipment and its maintaining & operation, make the network more flexible and smart, SDN based control/orchestration/management should be considered. Here in this contribution we focus on the data plane architecture thus do not discuss much about this aspect.
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G.mtn is compatible with the Ethernet ecosystem and based on slicing the Ethernet core.  IEEE 802.3 Ethernet PHYs have been proven as successful interface technologies evolved from 100M fast Ethernet, Gigabit Ethernet to 10GE. Most economically feasible building blocks for STL are single lane standardized 802.3 Ethernet optical PHYs, 10GBASE-LR/25GBASE-LR/50GBASE-LR up to 10km and 10GBASE-ER/25GBASE-ER/50GBASE-ER up to 40km. Higher data rate beyond 50G Ethernet PHYs such as 100GE, 200GE and 400GE are mainly multilane bonding architecture with 25Gbps or 50Gbps per lane [1]. There are also some economically feasible off the shelf grey optical module (but non-standard) for Ethernet, such as 80km ZR for 10GE/25GE or higher rate multi-lane PHYs with 10/25Gbps per lane in addition to the standard Ethernet PHYs. All these Ethernet PHYs share a common component ecosystem thus have a great advantage on their economic feasibility.
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At the October ITU-T SG15 plenary session in Geneva, Chinese network operators, equipment vendors, and research institutes submitted several proposals for 5G network transport technology solutions.  From Contribution 1034 by China Mobile and other China resident companies: A proposal to initiate a new work item on Management Aspects for SPN: 

Slicing Channel Layer (SCL) is defined as a path layer. Many SPN contributions have been presented in previous ITU-T SG15 meetings which clearly showed that SPN can be an appropriate candidate solution for 5G transport.,,

It is proposed that Q12, Q14 start a new work item on management aspects for 5G transport networks. It shall address management aspects of SPN network elements containing transport functions for the SCL and SPL layers. The same management architecture and tools for traditional transport networks such as MPLS-TP and OTN shall be reused as much as possible. The management functions for fault management, configuration management and performance monitoring shall be specified.

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Based on the above proposals (led by China Mobile),  ITU-T SG 15 approved G.mtn standard initialization of the SPN forwarding plane technology.   China Mobile persuaded industry experts attending the SG 15 meeting that SPN has advantages in terms of 5G transport capability, key technical feasibility and industrialization, ZTE and China Mobile said in a statement.

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Transport Network support of 5G:  An updated version of Technical Report GSTR-TN5G, Transport network support of IMT-2020/5G, was agreed. This report captures requirements for Transport Network support of 5G mobile fronthaul, middle-haul, and backhaul networks. A new Recommendation was completed on Radio over fiber systems, and a new Supplement on 5G Wireless Fronthaul Requirements in a PON Context.  New Recommendations G.8262.1 and Amendment 2 to G.8273.2 that specify new clocks to support synchronization for IMT-2020/5G were consented.

References:

https://www.zte.com.cn/global/about/press-center/news/201811/20181102

https://www.linkedin.com/pulse/itu-t-created-new-work-item-gmtn-spn-weiqiang-cheng

https://www.telecomasia.net/content/itu-t-initializes-gmtn-standardization

https://www.itu.int/en/ITU-T/studygroups/2017-2020/15/Pages/exec-sum-201810.aspx

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