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.
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