Options for time-sensitive networking for 5G fronthaul

Options for time-sensitive networking
for 5G fronthaul
Jim Zou, Adrian Sasu, John Messenger, and Jörg-Peter Elbers
23 September, 2019

© 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

Outline
1
2
3
4

~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
CU: central unit
RU: radio unit
CU: central unit
~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

• 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

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.)

From CPRI to eCPRI
eCPRI leverages Eth transport & OAM and offers ~10x reduction in bandwidth

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

Outline
1
2
3
4

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

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

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

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

IEEE 1588v2 PTP
What is PTP

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

Outline
1
2
3
4

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

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

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

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

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

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

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

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

Outline
1
2
3
4

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

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)

Live demo @ EuCNC’19
Frame preemption (802.1Qbu) on one-way traffic path

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

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.

Options for time-sensitive networking for 5G fronthaul

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