Options for time-sensitive networking for 5G fronthaul
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The document discusses the options for time-sensitive networking (TSN) in 5G fronthaul, highlighting the critical importance of low latency, accurate timing, and high bandwidth for effective communication in mobile networks. It reviews various TSN standards and their roles in ensuring deterministic Ethernet transport while addressing the challenges of functional splits and synchronization across network components. The need for innovation in implementing these standards to meet the evolving demands of 5G networks is emphasized.
Options for time-sensitive networking for 5G fronthaul
- 1. Options for time-sensitive networking for 5G fronthaul Jim Zou, Adrian Sasu, John Messenger, and Jörg-Peter Elbers 23 September, 2019
- 2. © 2019 ADVA Optical Networking. All rights reserved.22 Outline Fronthaul in 5G RAN – time matters Time sensitive networking (TSN) – deterministic Ethernet transport Research activities and ongoing works 1 2 3 4 Ethernet-based fronthaul – yet accurate timing delivery Summary and outlook5
- 3. © 2019 ADVA Optical Networking. All rights reserved.33 Outline Fronthaul in 5G RAN – time matters Time sensitive networking (TSN) – deterministic Ethernet transport Research activities and ongoing works 1 2 3 4 Ethernet-based fronthaul – yet accurate timing delivery Summary and outlook5
- 4. © 2019 ADVA Optical Networking. All rights reserved.44 ~1ms round-trip time ~5ms round-trip time ~10ms round-trip time Very low latency Low latencyUltra low latency Latency determines location of RAN functions, but no one-fits-all configuration. … and time-critical services require deterministic latency Time matters… RU: radio unit DU: distributed unit CU: central unit MEC: multi-access edge computing UPF: user plane function RU: radio unit DU: distributed unit CU: central unit MEC: multi-access edge computing UPF: user plane function RU: radio unit DU: distributed unit CU: central unit MEC: multi-access edge computing UPF: user plane function ~1000 sites ~100 sites ~10 sites ~1000 sites ~100 sites ~10 sites ~1000 sites ~100 sites ~10 sites Source: NGMN Overview on 5G RAN Functional Decomposition
- 5. © 2019 ADVA Optical Networking. All rights reserved.55 • New functional split options • Network slicing for different applications • Challenging to balance between HLS and LLS • No consensus yet on a single LLS in 3GPP • LLS options defined in eCPRI, O-RAN, SCF • Timing and synchronization • High bandwidth and low latency requirements for fronthaul transport 5G requires high-bandwidth, low-latency, accurate-timing transmission Disruption in 5G RAN functional splits Source: ITU-T G.Sup66
- 6. © 2019 ADVA Optical Networking. All rights reserved.66 3GPP IEEE 802.1CM eCPRI New standards for 5G fronthaul O-RAN Higher Layer Functional Split (HLS) TSN for Fronthaul Ethernet Transport Requirements Lower Layer Functional Split (LLS): O-RAN 7.2x Ethernet becomes convergence layer for 5G transport And more… (IEEE 1914.1&3, MEF 5G project, IETF DetNet, etc.)
- 7. © 2019 ADVA Optical Networking. All rights reserved.77 From CPRI to eCPRI eCPRI leverages Eth transport & OAM and offers ~10x reduction in bandwidth
- 8. © 2019 ADVA Optical Networking. All rights reserved.88 Ethernet-based data delivery combined with precise time distribution … with additional timing accuracy requirements eCPRI leverages Ethernet transport… CoS Traffic Max. one- way frame delay Use case Max. one- way frame loss ratio High25 User plane (fast) 25µs Ultra-low latency applications 10-7 High100 100µs Full LTE or NR performance High200 200µs Installations with long fiber links High500 500µs Large latency installations Medium User plane (slow), C&M plane (fast) 1ms All 10-7 Low C&M plane 100ms All 10-6 Category Maximum time error |TE| at UNI Maximum time alignment error TAE between antenna ports T-TSC in radio equipment T-TSC in transport network T-TSC with |TEmax|=70ns (Class B) T-TSC with |TEmax|=15ns A+ (relative) n/a n/a 20ns 65ns A (relative) n/a 60ns 70ns 130ns B (relative) 100ns 190ns 200ns 260ns C (absolute) 1100ns 3µs
- 9. © 2019 ADVA Optical Networking. All rights reserved.99 Outline Fronthaul in 5G RAN – time matters Time sensitive networking (TSN) – deterministic Ethernet transport Research activities and ongoing works 1 2 3 4 Ethernet-based fronthaul – yet accurate timing delivery Summary and outlook5
- 10. © 2019 ADVA Optical Networking. All rights reserved.1010 Time in Ethernet The “best effort delivery” in Ethernet means • Transfer data as quickly as possible • Statistic multiplexing gain • Average delay Ethernet needs to be augmented when deterministic latency matters (e.g. 5G fronthaul) • Bounded maximum delay (not average) • Precise time of day delivery and phase alignment
- 11. © 2019 ADVA Optical Networking. All rights reserved.1111 Time in Ethernet Packet delay variation (PDV) Packet delay variation is caused by: • Random variation in delay results from the behavior of switches or routers in the packet network. • The primary source of this is output queuing delay, caused when a packet arrives at a switch or router when the exit port is blocked by other traffic, and the packet has to wait in a queue Source: ITU-T G.8261/Y.1361
- 12. © 2019 ADVA Optical Networking. All rights reserved.1212 Ethernet-based fronthaul Delay components through an Ethernet path Dimension the network for the slowest packet (peak delay) • Peak delay limiting the reach/distance between the remote unit and compute resource • Peak PDV needs to be smoothed out/compensated at receiver side through buffering RU EPC/ Metro/ Core Network RU RU RU Packet switch Packet switch RU CU CU vEPC CU vBBU Ethernet-based Mobile Transport Network End-to-end delay and packet delay variation (PDV) Propagation delay Bridging/Aggregation delay and PDV MEC/CO Packet switch Buffering delay • playout buffer for removing the PDV • Rx_window = Tx_window + PDV • equalize max delay of active and protection paths Bridging/Add delay and PDV Courtesy of R. Veisllari, TransPacket AS
- 13. © 2019 ADVA Optical Networking. All rights reserved.1313 Just a second: can Ethernet be synchronized? ITU-T Synchronous Ethernet (SyncE) • Bit-layer clock recovery solution similar to SDH/SONET • Highly robust, and not affected by network loading Reliable but only provides frequency sync, requires L1 support in every node IEEE 1588v2 – Precision Time Protocol (PTP) • Packet-based layer 2/3 protocol • Mechanism for end-to-end frequency and time alignment • Application profiles specified from the full standard • ITU-T Telecom Profiles for frequency (G.8265.x) & time and phase synchronization (G.8275.x) Phase and time alignment (and frequency where no SyncE) SyncE + PTP are used together as a stack to give the highest accuracy (f, t, θ) Ethernet sync distribution technologies
- 14. © 2019 ADVA Optical Networking. All rights reserved.1414 IEEE 1588v2 PTP What is PTP
- 15. © 2019 ADVA Optical Networking. All rights reserved.1515 IEEE 1588v2 PTP how does it work? SlaveGrand Master T1 T2 T3 T4 T4 Delay_SM Offset from Master = 𝑇2 − 𝑇1 + (𝑇4 − 𝑇3) 2 Packed-based mechanism for sync distribution Exchange sync messages between • “Grand Master” – central office clock • “Slave” – cell site Supports frequency, phase, and time sync T2 = T1 + Delay_MS + Offset T4 = T3 + Delay_SM – Offset Offset Robust implementations are needed to minimize impact of delay asymmetry and latency variations
- 16. © 2019 ADVA Optical Networking. All rights reserved.1616 Outline Fronthaul in 5G RAN – time matters Time sensitive networking (TSN) – deterministic Ethernet transport Research activities and ongoing works 1 2 3 4 Ethernet-based fronthaul – yet accurate timing delivery Summary and outlook5
- 17. © 2019 ADVA Optical Networking. All rights reserved.1717 What is IEEE 802.1 TSN? Objectives • Timing Synchronization: network-wide clock reference • Reduced latency: limited and deterministic network delays • Reduced loss: target is zero loss from congestion for TSN streams • Prevent non-time-sensitive traffic from interfering with time-sensitive traffic • Additional functionality to Ethernet Implementation • The IEEE 802.1 TSN Task Group is “responsible for developing standards that enable time- sensitive applications over IEEE 802 networks” • The primary projects are focused on • queuing and forwarding of time-sensitive streams • registration and reservation of time-sensitive streams • time synchronization • overall system architecture
- 18. © 2019 ADVA Optical Networking. All rights reserved.1818 Data transport with bounded low latency, low delay variation, and extremely low loss TSN overview Admission Control 802.1Qat – Stream Reservation Protocol (SRP) 802.1Qcc – SRP enhancements and performance improvements Deterministic traffic • Latency • Delay variation Redundancy Synchronization Scheduling 802.1AS-Rev – Timing and Synchronization (including profile of IEEE 1588-2008) 802.1Qbv – Enhancements for Scheduled Traffic 802. 1Qbu – Frame Pre-emption 802. 1Qch – Cyclic Queuing and Forwarding Reliability 802.1CB – Frame Replication and Elimination for Reliability 802.1Qci – Per-Stream Filtering and Policing Guaranteed traffic Automated configuration Profile 802.1CM – TSN for fronthaul
- 19. © 2019 ADVA Optical Networking. All rights reserved.1919 Traffic scheduling and shaping 802.1Qbv Enhancements for Scheduled Traffic (time-aware shaping) Requirements: time synchronization (IEEE 802.1AS or similar) fully managed network, making switches aware of cycle time for protected (or scheduled) traffic Time … … Without guard band Protected section Best effort section periodic window Interfering packet pushes the priority packets outside the window! Time Protected section Best effort section Guard band … … With guard band
- 20. © 2019 ADVA Optical Networking. All rights reserved.2020 Traffic scheduling and shaping 802.1Qbu/802.3br Frame Preemption and Interspersing Express Traffic Preemption= reducing the guard band by interrupting and preempting the transmission of a low priority packet • Min fragment size is 64 Byte (124 Byte incl. mCRC) Time Guard band … … Interfering Time Guard band (much reduced) … … 1 2
- 21. © 2019 ADVA Optical Networking. All rights reserved.2121 Traffic scheduling and shaping 802.1Qch: Cyclic Queuing and Forwarding Time Cycle 0 bridge 0 bridge 1 bridge 2 bridge 3 Cycle 1 Cycle 2 Cycle 3 D4 D1 D3 D2 D2 D4 D3 D4 D3 D4 Bridge 1 double cycle (with respect to example packet) Bridge 1 reception cycle (with respect to example packet) Bridge 1 transmission cycle (with respect to example packet) Related Stream Unrelated Stream Best effort Legend Upper bound latency = sum of per hop delays
- 22. © 2019 ADVA Optical Networking. All rights reserved.2222 Standards at a glance… but not exhaustive TSN is a collection of standards and ongoing topic Designation Title Incorporation 802.1Qat Stream reservation protocol 802.1Q-2011 802.1Qav Forwarding and queuing enhancements for time-sensitive streams 802.1Q-2011 802.3br Interspersing express traffic Standalone standard 802.1Qbu Frame preemption 802.1Q-2018 802.1Qbv Enhancements for scheduled traffic 802.1Q-2018 802.1Qci Per-stream filtering and policing 802.1Q-2018 802.1Qch Cyclic queuing and forwarding 802.1Q-2018 802.1CB Frame replication and elimination for reliability Standalone standard 802.1CM Time-sensitive networking for fronthaul Standalone standard P802.1Qcr Asynchronous traffic shaping 802.1Q amendment project P802.1Qcc SRP enhancements and performance improvements 802.1Q amendment project P802.1AS-Rev Timing and synchronization for time-sensitive applications – revision Standalone project
- 23. © 2019 ADVA Optical Networking. All rights reserved.2323 The IEEE 802.1 TSN standards set is like a toolbox or extended Swiss knife • Need to know what tools are available • Need to learn what each tool does • Lastly, what its “cost” is TSN profile selects features and options for a particular application, easing inter- operability and deployment Luckily, we do not have to use all the tools for mobile fronthaul! TSN components and profiles TSN 802.1BA Audio-Video Bridging (AVB) Profiles Industrial Automation 802.1CM Fronthaul
- 24. © 2019 ADVA Optical Networking. All rights reserved.2424 802.1CM TSN for fronthaul TSN profile to enable the transport of fronthaul streams in a bridged network Fronthaul over bridged Ethernet eRE/RE eRE/RE eRE/RE eREC/REC eREC/REC • Class 1: CPRI v7.0 • Class 2: eCPRI • Profile A: strict priority scheduling • Profile B: extends Profile A by adding frame pre-emption based on the 802.1Qbu • Requirement collection • Guidance for how to combine, configure, and use the selected TSN features to meet fronthaul requirements
- 25. © 2019 ADVA Optical Networking. All rights reserved.2525 Outline Fronthaul in 5G RAN – time matters Time sensitive networking (TSN) – deterministic Ethernet transport Research activities and ongoing works 1 2 3 4 Ethernet-based fronthaul – yet accurate timing delivery Summary and outlook5
- 26. © 2019 ADVA Optical Networking. All rights reserved.2626 FUSION: gap preservation So far, most TSN standards aim at deterministic delay through multi-hop network bridging, but not the minimum PDV in case of statistical multiplexing FUSION, an integrated hybrid (packet/circuit) optical network provided by TransPacket, preserve the gaps in the high priority stream by applying a fixed delay Fronthaul traffic carried as GST, i.e. by the “Circuit” Service Less delay-sensitive traffic carried through SM, e.g. Backhaul Input 100GE bypass as GST High- throughput on the line Fixed Delay SM Queues Gap Detector SM Scheduler N x 10GE
- 27. © 2019 ADVA Optical Networking. All rights reserved.2727 Live demo at ECOC’18 (Best Demo Award) Low-latency timing-accurate mobile x-haul based on SDN-enabled 100G Ethernet aggregator RoE BH TrafficAnalyzer 10G 100G100G 10G 1G IEEE 1588v2 PTP (grand master) IEEE 1588v2 PTP slave (probe) 10G10G 10G10G 10G 10G BBU GNSS RRH PTP 10G 10G Central Office Remote Node … RoE RoE NETCONF/YANG Controller 100G100G FUSION IP Core MAC 100G PHY MAC 10G PHY MAC 10G BH … x6…8 10G PHY 100G MAC100G PHY FUSION IP Core MAC MAC 100G Aggregator Node (time sensitive) 1G PTP 100GMAC 100G PHY 10G PHY MAC10G FH 10G FH … x4 1G PHY 10G PHY … 10G 10G … Backhaul Service Configuration and Monitoring … … … PTP TrafficEmulator … Traffic Generator 100G Transport Node (time sensitive) … … SM GST 100GbE ingress treated as GST FH bounded delay aggregation Dagg = Store-fw MTU@10G + serve all other streams (F 1) MTU@100Gbps + transmission of packet MTU@100Gbps 100G 1G ECOC Paper Tu3B.3 Fronthaul traffic (1522 Byte MTU) • <3.1µs agg+deagg latency (1µs from MAC/PHY) • <0.6µs transit node latency • 5µs per fiber-km IEEE 1588v2 PTP traffic • <±75ns time error (w/o additional means)
- 28. © 2019 ADVA Optical Networking. All rights reserved.2828 Live demo @ EuCNC’19 Frame preemption (802.1Qbu) on one-way traffic path
- 29. © 2019 ADVA Optical Networking. All rights reserved.2929 © 2019 ADVA Optical Networking. All rights reserved.29 Summary and outlook
- 30. © 2019 ADVA Optical Networking. All rights reserved.3030 More work is needed to convert those efforts into commercial products Summary and outlook 1 • Ethernet becomes the convergence layer for next-generation x-haul 2 • Low latency and precise timing delivery are critical requirements for FH 3 • TSN standards1 provide a toolbox and set the baseline for realization 4 • Options for innovation exist in the implementation2 1 IEEE 802.1CM 2 reduced delay variation, latency-aware network planning, latency measurement, and service assurance
- 31. Thank you / Vielen Dank / 谢谢 IMPORTANT NOTICE The content of this presentation is strictly confidential. ADVA Optical Networking is the exclusive owner or licensee of the content, material, and information in this presentation. Any reproduction, publication or reprint, in whole or in part, is strictly prohibited. The information in this presentation may not be accurate, complete or up to date, and is provided without warranties or representations of any kind, either express or implied. ADVA Optical Networking shall not be responsible for and disclaims any liability for any loss or damages, including without limitation, direct, indirect, incidental, consequential and special damages, alleged to have been caused by or in connection with using and/or relying on the information contained in this presentation. Copyright © for the entire content of this presentation: ADVA Optical Networking. jzou@advaoptical.com This work is funded by the European Union’s Horizon 2020 research and innovation program.