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Can OTN Be Replaced By Ethernet? A 5G Perspective

Optical Transport and access network requirements

There are two main drivers putting strict delay requirements on mobile fronthaul for 5G networks: the delay sensitive services targeted by the 5G network, and the fronthaul design itself. The figure above illustrates the maximum tolerable delay of some delay-sensitive applications that will need to be supported by both future backhaul and fronthaul networks. As seen in the figure, there are applications tolerating delays of 1 ms or less among the 5G target applications. The delay requirements in eCPRI-based fronthaul are even stricter. For fronthaul transport with split in the physical layer, as found in CPRI over Ethernet [6] and in eCPRI option “D” and “E” [4], the Hybrid Automatic Retransmit reQuest (HARQ) protocol sets restrictions on maximum delay between the RRH and BBU. In [7], a one-way delay of 123 microsecond is found as the maximum. In [4] and [8] an even stricter delay requirement of 100 microsecond one-way delay is set as a requirement.

Table 1. Comparison of features for OTN and Ethernet


Summary and conclusion

In this paper OTN and Ethernet network functionality has been compared with respect to applications including longhaul, metro, access and mobile fronthaul and backhaul. Because OTN natively defines how to frame a number of different protocols into OTN frames, it is more suitable than Ethernet for transport of legacy services. We expect however this to become less relevant for future networks. We find that using the functionality added to Ethernet through Carrier Ethernet, it now offers the same level of OAM functionality as OTN. Furthermore, OTN with static multiplexing supports a zero packet loss, low and fixed latency transport with full isolation between services. This is however also achieved in Ethernet using the IHON mechanisms. Furthermore, while providing the same level of deterministic service as OTN, Ethernet may additionally allow higher throughput utilization through statistical multiplexing using IHON mechanisms. OTNs Forward Error Correction capability is known to extend the reach of long-haul transport and is available for all OTN rates. For high Ethernet rates, 100 Gb/s and beyond, FEC is added, opening up for the same benefits as earlier only found for OTN. For these bitrates current maximum distance defined for Ethernet is 10 km.

OTN therefore shows benefits for legacy service and long-haul transport. For network segments less sensitive to physical transmission impairments, including metro, access and mobile backhaul and fronthaul, we find Ethernet to deliver the same level of service quality and availability while supporting a higher throughput efficiency than OTN. Hence, our conclusion is that today Ethernet is a beneficial choice for mobile transport, access and metro networks while only OTN is defined for high bitrate long-haul transport. Furthermore, as Ethernet today also contains FEC, up to now the prime OTN benefit for longhaul, it may replace OTN in the future for long-haul if IEEE chooses to define long-haul Ethernet interfaces.

Acknowledgment

This work is part of research project 5G-PICTURE supported by the European Horizon 2020 initiative.

References

[1]   ITU-T, G. 709, Interfaces for the optical transport network. June 2016.

[2]   A. Pizzinat et al., "Things You Should Know About Fronthaul", IEEE/OSA J. Lightwave Technol., vol. 33, 2015, pp. 1077-1083.

[3]   A. Checko et al., "Cloud RAN for Mobile Networks—A Technology Overview", IEEE Comm. Surveys & Tutorials, vol. 17, no. 1, 2015, pp. 405-426.

[4]   Common Public Radio Interface (CPRI) Specification, Sept. 2017, http://www.cpri.info/spec.html.

[5]   Nokia, “5G ultra-low latency infographics”, Aug. 2017;       https://resources.ext.nokia.com/asset/201030.

[6]   IEEE Std. P1914.3, “Radio Over Ethernet Encapsulations and Mappings,” Sept. 2009; http://sites.ieee.org/sagroups-1914/p1914-3/

[7]   H. J. Son, and S.M. Shin, “Fronthaul Size: Calculation of maximum distance between RRH and BBU”, Sept. 2017; http://www.netmanias.com/en/post/blog/6276/c-ran-fronthaul-lte/fronthaul-size-calculation-of-maximum-distance-between-rrh-and-bbu.

[8]   IEEE Std. P802.1CM, “Time Sensitive Networking for fronthaul”, Sept. 2017; http://www.ieee802.org/1/pages/802.1cm.html. .

[9]   Fujitsu white-paper: “The key benefits of OTN”, available online: https://www.fujitsu.com/us/Images/OTNNetworkBenefitswp.pdf, accessed 27/01-2018.

[10] Viavi white-paper: Andreas Schubert “G.709 – The optical transport network (OTN)”, available online: https://www.viavisolutions.com/en-us/literature/g709-optical-transport-network-otn-white-paper-en.pdf, Accessed 27/1-2018.

[11] Fujitsu white-paper: “Carrier Ethernet essentials”, available online: https://www.fujitsu.com/us/Images/CarrierEthernetEssentials.pdf, accessed 27/1-2018.

[12] IEEE 802.1Q standard “IEEE 802.1Q bridges and bridged networks”

[13] R. Veisllari et al., “Field-Trial Demonstration of Cost Efficient Sub-wavelength Service Through Integrated Packet/Circuit Hybrid Network [Invited]”, IEEE/OSA J. Opt. Comm. Net., vol. 7, no. 3, Mar. 2015, pp A379-A387.

[14] IEEE Std. P802.1Qbu, “Standard for Local and Metropolitan Area Networks-Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks - Amendment: Frame Preemption”, Jul. 2015; http://www.ieee802.org/1/pages/802.1bu.html.

[15] IEEE Std. 802.1Qbv, “Standard for Local and Metropolitan Area Networks-Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks Amendment: Enhancements for Scheduled Traffic”, Mar. 2016; http://www.ieee802.org/1/pages/802.1bv.html

[16] IEEE Std. 1588-2008, “Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems”, Jul. 2008.

[17] ITU-T recommendation Y-1731 “Performance monitoring in a service provider network”

[18] IEEE 802.1ag: IEEE 802.1ag (also CFM) (IEEE Standard for Local and Metropolitan Area Networks Virtual Bridged Local Area Networks Amendment 5: Connectivity Fault Management”

[19] IEEE 802.3bm: “IEEE Standard for Ethernet Amendment 3: Physical Layer Specifications and Management Parameters for 40 Gb/s and 100 Gb/s Operation over Fiber Optic Cables - IEEE Standard for Ethernet - Amendment 3: Physical Layer Specifications and Management Parameters for 40 Gb/s and 100 Gb/s Operation over Fiber Optic Cables.”

[20] IEEE 802.3bs-2017: “IEEE Std 802.3bs-2017 (Amendment to IEEE 802.3-2015 as amended by IEEE's 802.3bw-2015, 802.3by-2016, 802.3bq-2016, 802.3bp-2016, 802.3br-2016, 802.3bn-2016, 802.3bz-2016, 802.3bu-2016, 802.3bv-2017, and IEEE 802.3-2015/Cor1-2017) - IEEE Standard for Ethernet Amendment 10: Media Access Control Parameters, Physical Layers, and Management Parameters for 200 Gb/s and 400 Gb/s Operation.”

[21] R. Veisllari et al., “Experimental Demonstration of 100 Gb/s Optical Packet Network for Mobile Fronthaul with Load-independent Ultra-low Latency”, In proceedings of ECOC 2017.




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