Field and laboratory trials of 400GBASE‐LR8 over fibre distances up to 35 km
2018; Institution of Engineering and Technology; Volume: 54; Issue: 22 Linguagem: Inglês
10.1049/el.2018.6319
ISSN1350-911X
AutoresYu Rong Zhou, K. Smith, Mike Gilson, Philip J. Brooks, Chris Cole, Chengpin Yu,
Tópico(s)Advancements in PLL and VCO Technologies
ResumoElectronics LettersVolume 54, Issue 22 p. 1288-1290 Optical communicationFree Access Field and laboratory trials of 400GBASE-LR8 over fibre distances up to 35 km Y.R. Zhou, Corresponding Author Y.R. Zhou yu.zhou@bt.com BT Technology, British Telecommunications, Adastral Park, Ipswich, IP5 3RE United KingdomSearch for more papers by this authorK. Smith, K. Smith BT Technology, British Telecommunications, Adastral Park, Ipswich, IP5 3RE United KingdomSearch for more papers by this authorM. Gilson, M. Gilson BT Technology, British Telecommunications, Adastral Park, Ipswich, IP5 3RE United KingdomSearch for more papers by this authorP. Brooks, P. Brooks Viavi Solutions, Deutschland Gmb H, Eningen, GermanySearch for more papers by this authorC. Cole, C. Cole Advanced Development, Finisar, 1389, Moffett Park Drive, Sunnyvale, CA, USASearch for more papers by this authorC. Yu, C. Yu Advanced Development, Finisar, 1389, Moffett Park Drive, Sunnyvale, CA, USASearch for more papers by this author Y.R. Zhou, Corresponding Author Y.R. Zhou yu.zhou@bt.com BT Technology, British Telecommunications, Adastral Park, Ipswich, IP5 3RE United KingdomSearch for more papers by this authorK. Smith, K. Smith BT Technology, British Telecommunications, Adastral Park, Ipswich, IP5 3RE United KingdomSearch for more papers by this authorM. Gilson, M. Gilson BT Technology, British Telecommunications, Adastral Park, Ipswich, IP5 3RE United KingdomSearch for more papers by this authorP. Brooks, P. Brooks Viavi Solutions, Deutschland Gmb H, Eningen, GermanySearch for more papers by this authorC. Cole, C. Cole Advanced Development, Finisar, 1389, Moffett Park Drive, Sunnyvale, CA, USASearch for more papers by this authorC. Yu, C. Yu Advanced Development, Finisar, 1389, Moffett Park Drive, Sunnyvale, CA, USASearch for more papers by this author First published: 01 November 2018 https://doi.org/10.1049/el.2018.6319Citations: 3AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Successful experimental demonstration and field trial of 400GBASE-LR8 is reported based on 4-level pulse amplitude modulation format over standard G.652 single-mode fibre using CFP8 pluggable optical transceivers. Stable long-term error-free performance of 400GBASE-LR8 optical signal over fibre spools of varying lengths up to 35 km is demonstrated, which is significantly longer than the IEEE standard 802.3bs specification of 10 km reach. For the first time, error-free full throughput performance of 400GBASE-LR8 over a 27 km field fibre link including optical patch panels through operational exchanges is also demonstrated. The results demonstrate that this early 400GBASE-LR8 client technology is suitable for practical network deployment scenarios and has potential for even longer reach beyond the 10 km specification. Introduction Traffic continues to grow rapidly owing to high-speed broadband, video, cloud and data centre services. Coherent 100G has been widely deployed on the transmission line side to meet the increasing bandwidth demand. On the client side, Ethernet speeds have increased from 10 to 40 and 100 Gbit/s, and in the future towards Tbit/s as signposted in the Ethernet Alliance roadmap [1, 2]. In December 2017, IEEE approved 802.3bs Ethernet standard for 200 and 400 Gbit/s [3], in which one of the 400 Gbit/s Ethernet client interfaces defined is 400GBASE-LR8 for 10 km reach using single-mode fibre (SMF). So far simple non-return-to-zero (NRZ) signal format has mainly been used in client optics. For these higher Ethernet speeds, techniques commonly exploited to enhance the speed of line-side optics such as multi-level modulation formats and forward error correction (FEC) are now required in the client-side optics. In 400GBASE-LR8, 4-level pulse amplitude modulation format (PAM4) is used to increase the symbol rate, and FEC (e.g. KP4) is mandated in the standard [3], the first time for client optics. Different pluggable optical transceivers for 400GbE client interfaces are under research and development, and the multi-source agreement (MSA)-compatible CFP8 [4] is the first form factor available for 400GBASE-LR8. Other form factors such as quad small form factor pluggable – double density (QSFP-DD) and OSFP, are in advanced stages of development [5]. It is, therefore, important for network operators to understand the performance and suitability of these new technologies for practical network applications. Early interoperability demonstration of 400GBASE-LR8 CFP8 client interface were reported recently [6]. In this Letter, we report successful experimental demonstration and field trial of the new 400GBASE-LR8 client technology using CFP8 pluggable optical transceivers over standard G.652 SMF. Using optical fibre spools in the laboratory, we demonstrated stable, long-term error-free performance over different distances up to 35 km, which is significantly longer than the IEEE specified 10 km reach. We have also demonstrated, for the first time, error-free transmission of the 400GbE signal over a field fibre link of 27 km including several optical patch panels in an operational exchange environment. We show 400 Gbit/s Ethernet latency performance measured with full throughput using different Ethernet frame configurations. The 400GbE field demonstration shows real-world performance of the 400GBASE-LR8 client technology for practical network application with potential beyond the 10 km specification. Experimental configurations Fig. 1 shows the experimental configurations for 400GBASE-LR8 client technology demonstration, where Fig. 1a shows the setup using standard G.652 fibre spools in the laboratory and a variable optical attenuator (VOA) to adjust the signal power. A Viavi ONT 400G Ethernet tester and a Finisar CFP8 pluggable optical transceiver are used to generate the 400GBASE-LR8 PAM4 optical signal with KP4 FEC encoding. The CFP8 optical transceiver has a 16 lane electrical interface with 25G NRZ per lane. In the transceiver, a 16:8 physical layer (PHY) circuit converts 16 × 25G NRZ signals to 8 × 50G PAM4 electrical signals, which then modulate the eight wavelengths generated from directly modulated lasers on LAN-WDM grid [3]. The eight wavelength channels are combined in a WDM multiplexer in the transceiver to form the 400GBASE-LR8 signal, giving total 8 × 50 Gbit/s at a net baud rate of 25 GBaud. The 400GBASE-LR8 signal then transmits over optical fibre of varying length (10, 25 and 35 km) and the VOA. On the receive path, direct detection is used in the transceiver, where a WDM de-multiplexer separates the incoming wavelengths onto eight broadband PIN detectors followed by transimpedance amplifier and equalisation. An 8:16 PHY circuit then converts 8 × 50G PAM4 electrical signals back to 16 × 25G NRZ lanes. Fig. 1b shows the setup for 400GBASE-LR8 signal transmission over a field fibre link from BT labs at Adastral Park to BT's Ipswich exchange, where the fibre is standard G.652 SMF, looped back at Ipswich giving a total distance of 27 km. As illustrated in this figure, the 400GbE signal also transmits through several optical patch panels across both Adastral Park and Ipswich exchange, representative of a challenging operational environment. This results in a significantly higher total loss than the field fibre alone. Optical and Ethernet performances, for all layers including physical sublayer (PHYS), physical coding sublayer (PCS) and media access control/Internet protocol (MAC/IP), are evaluated using the 400G Ethernet tester. Fig 1Open in figure viewerPowerPoint Experimental configuration a Over fibre spools of different lengths b Over field fibre link with physical loopback of total 27 km Experimental results To understand the baseline performance of 400GBASE-LR8 pluggable optical transceivers, we measured the performance of two CFP8 transceivers in a back-to-back case with no optical fibre. Fig. 2 inset shows the measured optical spectrum for one of the 400GBASE-LR8 transceivers (module b in Fig. 2). As expected, we see eight wavelength channels (1272.9, 1277.52, 1281.72, 1286.14, 1295.72, 1300.22, 1305.14 and 1309.72 nm) with flatness ∼1 dB, well within the range specified in the IEEE standard. Both transceivers had similar optical spectral characteristics. The 400G Ethernet tester is used to measure the optical performance of the PAM4 optical signal, e.g. pre-FEC BER, the ratio of the total corrected bit errors to the total number of signal bits. Fig. 2 shows the pre-FEC BER as a function of optical signal power into the 400GBASE-LR8 optical transceivers. We see similar performance characteristics for both transceivers with a pre-FEC BER of ∼7.9 × 10−9 and ∼1.86 × 10−8 at the maximum powers of 12.9 and 13.2 dBm, respectively. As the signal power reduces, the pre-FEC BER stays about the same (∼10−8) until ∼6 dBm, and then slowly increases to ∼2 × 10−4. Post-FEC error-free performance was achieved until ∼ 2 × 10−4 for a received power as low as ∼−2 dBm. Fig. 2 clearly shows that both 400GBASE-LR8 optical transceivers have consistent performance with a total loss budget of ∼15 dB, equivalent to ∼40 km G.652 SMF in an ideal loss limited case. We carried out a set of experiments using various lengths of standard G.652 SMF up to 35 km. We first investigated the performance of 400GBASE-LR8 over a 10 km fibre spool using the CFP8 module b in Fig. 2. The maximum received signal power is ∼8.4 dBm due to a loss of ∼4.8 dB from the fibre and connectors. Compared to the back-to-back case, the pre-FEC BER increased slightly for signal powers between ∼8.4 and 2.3 dBm as shown in Fig. 3. As signal power decreases, the pre-FEC BER increases; however, the pre-FEC BER at signal power <1.5 dBm is slightly better than that in the back-to-back case. The small penalty observed at higher signal powers is caused by the dispersion induced signal distortion on the PAM4 signal, which has more significant impact at higher signal to noise ratio. At lower signal powers, receiver noise is the dominant factor in determining the BER performance compared with the dispersive distortion. Equalisation filtering in the transceiver improves the receiver sensitivity, resulting in slightly improved pre-FEC BER. Error-free performance was measured for the received power as low as −2.2 dBm. Hence, for the 10 km fibre, there is a large loss margin of ∼10.6 dB. We further investigated the performance of 400GBASE-LR8 with increased fibre lengths of 25 and 35 km also shown in Fig. 3. Owing to additional fibre loss, the maximum received signal power is reduced to 3.7 dBm for 25 km and −1 dBm for 35 km. Error-free performance was achieved with a loss margin of ∼6 dB for 25 km and ∼1.5 dB for 35 km. From these results, we show that the impact of fibre dispersion is small for the fibre distances investigated with optical loss as the dominant limitation. Fig 2Open in figure viewerPowerPoint Pre-FEC BER at different received powers in back-to-back case Fig 3Open in figure viewerPowerPoint Pre-FEC BER versus received signal power for different fibre distances We investigated the Ethernet performance of 400GBASE-LR8 over the various fibre lengths. In Table 1, we show the latency measurement results with full 400G throughput. A latency of ∼137 ns was measured in the back-to-back case reflecting the delay through the 400GbE tester and CFP8 transceiver. For transmission over optical fibre, we measured latency values of 50.27, 123.79 and 173.92 µs consistent with the fibre length of 10, 25 and 35 km, respectively. Full 400GbE throughput was measured in all these cases using different Ethernet frame configurations, e.g. fixed 64 bytes frame as well as random frame size between 64 and 1518 bytes. To understand the long-term performance, we measured the 400GBASE-LR8 signal over the various fibre distances for overnight or weekend. End-to-end error-free performance in all layers (PHYS, PCS and MAC/IP) with pre-FEC BER ∼2.3 × 10−5 was achieved for 400GBASE-LR8 transmission over 35 km for the measurement period of over 16 h. Similarly, we measured the long-term error-free performances for 10 km overnight (16 h) and 25 km over weekend (∼64 h). Table 1. 400GbE latency measurement for different fibre lengths Scenario Latency Back to back 137.56 ns 10 km fibre 50.27 µs 25 km fibre 123.79 µs 35 km fibre 173.92 µs Field link of 27 km 137.36 µs We further conducted a field trial demonstration of the 400GBASE-LR8 client technology over the 27 km field fibre link. On the transmission path, the 400GBASE-LR8 signal passes through several optical patch panels, resulting in an additional loss of over 4 dB. Error-free performance across all layers (PHYS, PCS and MAC/IP) was measured overnight for a period of over 22.5 h with the pre-FEC BER of ∼8.71 × 10−5. A latency of 137.36 µs was measured for the 400GbE signal transmission as given in Table 1, consistent with the field fibre distance of 27 km. In 400GBASE-LR8, standardised KP4 FEC is used which has a capability of correcting up to 15 errored symbols per codeword (each codeword contains 544 symbols and each symbol has 10 bits). We examined the FEC statistics of the corrected symbol errors per codeword for the 22.5 h measurement results. Fig. 4 shows the statistical distribution of the corrected symbol errors between 1 and 14, where 1.82958 × 1012 (77.82%) of the codewords have only a single errored symbol. Only a single codeword has 14 errored symbols, consistent with measured error-free performance during the 22.5 h measurement period. Fig 4Open in figure viewerPowerPoint Percentage of corrected codewords versus number of errored symbols per codeword over 27 km fibre link for 22.5 h measurement Conclusion In this Letter, we have described results from the successful experimental demonstration and field trial of 400GBASE-LR8 client technology using CFP8 pluggable optical transceiver over G.652 SMF. With optical fibre spools in the laboratory, we demonstrated stable long-term error-free full throughput performance of 400GbE over different distances up to 35 km, significantly longer than the specified 10 km reach. We also demonstrated for the first time error-free full 400GbE throughput over a 27 km field fibre link including several 'lossy' optical patch panels through operational exchanges. We show that the impact of fibre dispersion on the 400GBASE-LR8 PAM4 signal is small for the distances investigated and optical losses are the dominant limitation to the optical reach. These demonstrations give us good confidence that emerging 400GBASE-LR8 client technology is suitable for practical network applications with potential for even longer reach beyond the 10 km specification. Acknowledgments We thank colleagues J. Casey from Viavi and M. Fletcher from Laser 2000 for their help and support. References 1 Ethernet Alliance: ' The 2018 Ethernet roadmap'. Available at https://ethernetalliance.org/the-2018-ethernet-roadmap/, accessed September 2018 2Cole, C.: 'Beyond 100G client optics', Commun. Mag., 2012, 50, (2), pp. 558– 566 (https://doi/org/10.1109/MCOM.2012.6146486) 3 IEEE Standard 802.3bs: ' IEEE standard for Ethernet, amendment 10: media access control parameters, physical layers, and management parameters for 200 Gb/s and 400 Gb/s operation', 6th December 2017 4 CFP Multi-Source Agreement. Available at http://cfp-msa.org/documents.html, accessed September 2018 5 OFC 2018 post show report: ' The future of optical networking and communications, a market overview'. Available at https://www.ofcconference.org/library/images/ofc/2018/Documents/OFC-2018-Show-Report.pdf, accessed September 2018 6Birk, M., Nelson, L.E., Zhang, G. et. al.,: ' First 400GBASE-LR8 interoperability using CFP8 modules', OFC 2017, paper Th5B.7 Citing Literature Volume54, Issue22November 2018Pages 1288-1290 FiguresReferencesRelatedInformation
Referência(s)