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Handling Delay In 5G Ethernet Mobile Fronthaul Networks

5G networks put new strict requirements for low delay and delay variation in mobile fronthaul networks. The newly published eCPRI specification enables the use of Ethernet for the fronthaul transport network. However, one-way end-to-end delay through the network is specified to be less than 100 microseconds. Since Ethernet was not originally designed for strict delay requirements, this motivates the need for mechanisms specifically designed for Time Sensitive Networks. The maximum fiber distance between RRH and BBU in a point-to-point eCPRI network is therefore 20 km (5 microseconds/km fibre delay). Any bridge in the network path will insert delay and hence, reduce the available distance. Packet Delay Variation (PDV) must be removed in a playout buffer at the receiver side, further increasing delay and reducing available distance. The mechanisms discussed in this paper can remove PDV and reduce delay in Ethernet bridges. However, the benefit of taking new mechanisms into use must be carefully evaluated against the increased complexity and incompatibility it may cause. Increased complexity in configuration and scalability of the network is of prime concern for carriers implementing and operating the networks. In the paper, we examine the pros and cons of Integrated Hybrid Optical Network (IHON) (TransPacket FUSION) and IEEE TSN standardized mechanisms and give some examples on dimensioning of the network with respect to delay and PDV. We use a six node network consisting of an aggregation-node, four intermediate nodes, and a deaggregation node as an example network. 1 Gb/s Ethernet client interfaces are aggregated into an 10 Gb/s link which is bypassing through four nodes before being deaggregated to 1 Gb/s client interfaces. For both IHON/FUSION and IEEE TSN, the end-to-end added delay from the mechanisms in the nodes is found to be less than 17 microseconds. IHON/FUSION is found to give the lowest PDV and complexity, while the IEEE TSN mechanisms enables a lower delay, allowing an extra 2 km transmission distance in our example.


References

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

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

[3]   Common Public Radio Interface eCPRI Interface Specification V1.1

[4]   IEEE P1914.1, “Standard for Packet-based Fronthaul Transport Networks”

[5]   IEEE P1914.3, “Radio Over Ethernet Encapsulations and Mappings”

[6]   IEEE P802.1CM, “Time Sensitive Networking for fronthaul”

[7]   3GPP Tdoc R3-161380, “Motivation for standard interface between central and distributed units”

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

[9]   H. J. Son, and S.M. Shin, “Fronthaul Size: Calculation of maximum distance between RRH and BBU”, Sept. 2017; https://www.netmanias.com/en/?m=view&id=blog&no=6276&vm=pdf.

[10] 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

[11] 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

[12] 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

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


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