5g-oriented optical transport network solution
Post on 02-Oct-2021
14 Views
Preview:
TRANSCRIPT
5G-oriented Optical Transport Network Solution
Contents
Overview
5G Development Brings Challenges to Bearer Networks
Impact of 5G Network Architecture Changes on Bearer Networks
Fronthaul Network Solutions for the C-RAN Architecture
5G Fronthaul Network Changes and WDM/OTN Bearer Solution
Unified Backhaul of Fixed-Mobile Convergence and OTN Bearer Solution
SDN-Based Optical Networks Effectively Support the Slicing and Intelligent Operation of 5G Networks
OTN Key Technologies in 5G Bearer Network
Summary
Appendix
01
02
03
05
07
10
13
14
16
17
1
Overview
In recent years, the evolution of mobile networks
into 5G has become the industry focus. 5G will
penetrate into almost all areas of our future society.
The construction of the user-centric information
ecosystem will provide users with extreme service
experience. The ITU defined three major application
scenarios for 5G: Enhanced Mobile Broadband (eMBB),
Massive Machine Type Communication (mMTC), and
Ultra Reliable Low Latency Communication (uRLLC).
These scenarios no longer simply emphasize the peak
transmission rate, but consider the eight key capabilities:
peak rate, user experience rate, spectrum efficiency,
mobility, latency, connection density, network energy
efficiency, and traffic density. Different application
scenarios have different technical requirements. In
general, the 5G technology is quite different from
previous wireless communication technologies in the
bandwidth, latency, number of connections, high-speed
mobility and other aspects. Through 5G, performance
indicators can be greatly improved.
2
5G Development Brings Challenges to Bearer Networks
ITU 5G key capabilities Key capabilities in different scenarios
As the application scenarios are becoming gradually
clear, standards development is accelerating, and
breakthroughs are continuously made in technology
research and development. The commercial use of
5G networks is just around the corner. 5G wireless
5G wi l l have a wider wire less spec trum and
use massive MIMO, high-order QAM and other
technologies to improve bandwidth of air interface.
With a high frequency band, the bandwidth for 5G
networks can even reach tens of Gbps. Compared
with 4G networks, the peak bandwidth and user
experience bandwidth of 5G networks is 10 times
Figure 1 5G Application Scenarios and Key Capabilities
higher, and eMBB services including HD video and VR/
AR can be provided more easily. However, 5G requires
10 times higher bandwidth for bearer networks.
In the 5G era, the Tactile Internet, automatic driving
and other services will gradually be introduced and
popularized. These uRLLC services require an end-to-
network construction requires the support and
cooperation of bearer networks to meet the
requirements of 5G application scenarios and key
capabilities, and to continue to be evolved and
developed.
3
end latency shorter than 1 ms. The latency assigned to
bearer networks should be even shorter. The existing
bearer network equipment and networking modes
must be optimized to reduce the latency and meet
new service development requirements.
5G networks have the same requirements for frequency
synchronization as LTE networks. However, 5G networks
have put forward higher requirements for time
synchronization. Compared with the +/- 1.5 microseconds
required by LTE networks, the time synchronization
precision required by 5G networks is improved by more
than one order of magnitude. 5G networks must support
1.The core network is based on cloud and deployment
is virtualized.
The control plane and user plane of the core network
are separated. The user plane is moved downwards
and has evolved from a centralized plane into a
decentralized plane. Through the virtualization
technology, the physical entities of the core network
are separated into multiple virtual network elements,
which are deployed based on cloud in the network.
In this way, their geographical positions are closer to
high-precision time synchronization.
The network slicing concept is put forward for
5G. To meet the different requirements of eMBB,
mMTC, uRLLC and other services for the bandwidth
and latency, different network resources should be
allocated. This requires that 5G bearer networks
provide the network slicing capability to flexibly
and dynamically allocate and release the network
resources required by different ser vices, and
dynamical ly opt imize net work connec t iv i t y,
reduce the costs of the ent i re net work , and
enhance efficiency.
terminals and the latency can be reduced.
2.There will be more C-RANs.
In the 3G/4G era, C-RANs have showed advantages
in overall cost reduction, wireless collaborative anti-
interference, energy saving, O&M simplification and
other aspects. However, C-RANs were not deployed
on a large scale. The C-RAN architecture used in the 5G
stage facilitates flexible wireless resource management,
allows functions to be deployed flexibly to meet the
Impact of 5G Network Architecture Changes on Bearer Networks
Compared with the 4G network architecture, the 5G network architecture has the following changes:
4
requirements of mobile edge computing, supports
hardware and software decoupling, and enhances the
software capabilities of wireless networks.
3.The base station density is higher.
5G uses a new spectrum. The 3.5 GHz, and 6 GHz+
frequency bands are higher than the existing 3G/4G
frequency bands. Theoretically, the coverage range
is smaller and more base stations are required. In
hot spot areas with high capacity, ultra-dense base
stations are used in networks
These changes of the 5G network architecture
have also resulted in impact to bearer networks:
The service anchor point of the core network is moved
downwards, and the backhaul network is flatter.
The C-RAN architecture has resulted in more
fronthaul networks, and they must meet the low
cost and flexible networking requirements.
F i b e r s a r e m o v e d d o w n w a r d s , a n d m o r e
transmission nodes need to be deployed.
Figure 2 5G Network Architecture Has Impact on Bearer Networks
5
1.Dark fiber
This method eliminates the need for transmission
equipment between the BBU and RRU, with the lowest
latency and simplest deployment. However, this
method uses a large number of fiber resources. When
base station density is increased in the 5G stage, fiber
resources will be insufficient. This solution refers to
point-to-point direct connections, it has no network
protection and cannot provide high reliability for the
uRLLC services.
2.Passive WDM
This method uses a passive optical multiplexer/
demultiplexer to multiplex many wavelengths to an
optical fiber for transmission. This can save valuable
fiber resources. The latency caused by optical
component is very small. Passive equipment does not
need to be powered on. Its maintenance is simple
and the cost is low. However, the RRU and BBU must
provide colored optical interfaces, which increase the
wireless equipment cost. In a ring network or chain
network, due to the accumulated insertion loss of
multiple passive WDM components, the optical power
budget is insufficient and the transmission distance is
limited. There is no OAM or fault management capability,
line protection is not provided in most cases.
3.WDM/OTN
This method uses WDM/OTN to achieve the multiplexing
and transparent transmission of the fronthaul signals
of multiple sites. It can save fiber resources, provides
OAM functions such as optical layer and electrical
layer performance management and fault detection,
provides network protection, and ensures high
service reliability. WDM/OTN is an L0/L1 transmission
technology, naturally with high bandwidth and
short latency features. This technology can achieve
short-latency transmission for all services at the
same time. The solution does not require wireless
equipment to support colored optical interface,
reducing the difficulties of wireless equipment
deployment. In addition, during the migration of an
established network from a non-C-RAN architecture to
the C-RAN architecture, the optical interfaces of the
wireless equipment do not need to be replaced. The
disadvantage is that the equipment cost is relatively
higher, and a low cost solution needs to be developed.
Fronthaul Network Solutions for the C-RAN Architecture
A variety of fronthaul network technologies can be used in the C-RAN architecture. Each of them has
advantages and disadvantages.
6
4.WDM PON
This method uses star networks. The fiber resources
deployed on the PON network access layer can be
used, and the equipment cost is low. The current
access rate can reach 10 Gbps, which is suitable for
the access of small cells. The related technologies and
standards are developing.
5.Ethernet
At present, the industry is also discussing the
Ethernet-based fronthaul solution. This method
uses packet technologies, and uses the statistical
multiplexing feature to achieve traffic convergence
and improve line bandwidth usage. It supports point-
to-multipoint transmission and saves fiber resources.
However, this solution needs to solve the problems
including identification and fast forwarding of short-
latency services and high-precision synchronization,
and needs to be compatible with CPRI signal
transmission which is based on the TDM technology.
The IEEE has set up the 802.1 TSN task group to study
the latency-sensitive Ethernet forwarding technology,
and set up the 1914 NGFI working group to study
CPRI over Ethernet and new Ethernet-based next
generation fronthaul interface.
Figure 3 Optional Fronthaul Network Technologies in the C-RAN Architecture
7
5G RAN functions are re-split. The original BBU and
RRU are reconstructed as three functional entities:
CU, DU, and RRU/AAU. The CU mainly provides the
non-real-time wireless high-level protocol processing
function such as radio resource management and dual
connection, it can use general hardware platform, and
be deployed together with mobile edge computing. A
DU mainly processes physical layer functions and the
real-time HARQ flow through a dedicated equipment
platform or a general+dedicated hybrid platform.
For large-scale MIMO antennas, some physical layer
functions can also be moved downwards to RRU/AAU
to significantly reduce the transmission bandwidth
between RRU/AAU and DU and reduce transmission
costs. The high-level function division solution
(between the CU and DU) focuses on OPTION2 and
OPTION3-1, which will be standardized in the near
future with bandwidth features close to those of
backhaul networks. The industry has not yet reached
a consensus on the standardization of the underlying
function division solution (between DU and RRU/
AAU). The standardization may be started when the
5G new radio interface protocols are mature and
stable enough. At present, there are NGFI, eCPRI and
other solutions in the industry. RRU with not too many
antenna channels can continue to use CPRI.
Dual connection, seamless switch over, radio
resource management.
Non-real-time processing.
Service oriented, ensure quality of services.
Real-time digital signal processing.
Real-time HARQ processing.
Radio oriented, ensure efficiency of
spectrum.
Part of PHY processing move to
RRU/AAU to reduce the BW of
fronthaul interface.
5G Fronthaul Network Changes and WDM/OTN Bearer Solution
Figure 4 RAN Function Re-Split
8
According to the different positions of the CU, DU, and RRU/AAU, there can be different fronthaul networking
modes, see Figure 5. The specific mode is determined by the operator's fiber distribution, room conditions,
O&M mode and other conditions.
Figure 5 Fronthaul Networking Modes
If DU and RRU/AAU are deployed on the same site,
they are connected directly through dark fibers. If
DU are centrally deployed, the connections between
DU and RRU/AAU correspond to level-1 fronthaul.
To meet the requirement of real-time DU processing
for the latency, the level-1 fronthaul distance should
be shorter than 10 km. In this case, you can use dark
fibers for direct connections, or use WDM/OTN to
save fibers and provide protection. The Muxponder
of WDM/OTN multiplexes the 10 Gbps or 25 Gbps
CPRI or eCPRI signals of multiple RRUs/AAUs into
100/200 Gbps high-speed signals and transfers them
to DU, meeting the high bandwidth transmission
requirement. As fiber routes can flexibly establish
point-to-point networks, chain networks, and ring
networks, the single-fiber bidirectional technology
can be used in a point-to-point network to save fibers.
DU pooling saves wireless equipment investment
while providing the best cooperative gain, see Figure
6. At present, the cost of level-1 fronthaul of the WDM/
OTN equipment is comparatively high. The reduction
of the cost is the key to the successful commercial use
of this scenario.
9
Figure 6 WDM/OTN Solution for Level-1 Fronthaul
The connection between the CU and DU correspond
to level-2 fronthaul, which is based on a ring network
in most cases. The WDM/OTN technology allows
wavelengths to pass the intermediate site on the
optical layer and achieve one-hop direct access,
meeting the high bandwidth and low latency
requirements. Optical channel protection can be
configured to meet reliable service requirements. As
the DU capacities of different transmission sites may
be different, different rates can be configured for the
wavelength of each transmission site to meet different
DU capacity requirements. In addition, each access
site can be individually expanded and upgraded
without affecting other sites. If OTN integrates the
packet function (Packet Enhanced OTN), service
convergence and flexible forwarding can be achieved
on the CU site, and the services of multiple DU can be
converged on the DU site.
With the same E-OTN equipment, the 100 Gbps
packet optical ring network solution can be provided.
For multiple sites with a small number of DU and light
traffic, ODUflex sub-wavelengths can be connected
to form a packet ring. Through multi-site service
statistics and multiplexing, bandwidth utilization
ratio can be improved. For the sites (DU pool) with
heavy traffic, ODUflex sub-wavelengths can be cross-
connected on the intermediate site and directly
access the CU site. Different types of services can use
different ODUflex slices for transmission. For example,
the eMBB service uses a packet ring network for
hop-by-hop forwarding, and the uRLLC service uses
L1 for direct access to reduce the latency. ODUflex
bandwidth can be flexibly adjusted by step of 1.25
Gbps. The total 100Gbps ring network bandwidth can
be flexibly allocated to multiple logical ring networks
on different sites.
10
Figure 7 E-OTN Solution for Level-2 Fronthaul
Unified Backhaul of Fixed-Mobile Convergence and OTN Bearer Solution
When mobile networks are evolving into 5G networks,
CO reconstruction is also in progress. Traditional Central
Offices are gradually transformed into localized edge
DCs. Based on the SDN/NFV technology, the dedicated
equipment of traditional NEs are replaced with
general hardware for cloud deployment. The user
plane of vEPC in the 5G core network will be moved
downwards, and deployed together with the vBNG,
vCPE, and vCDN of the fixed network in the edge DCs.
Through computing and storage resource sharing, the
number of equipment rooms and maintenance cost
can be significantly reduced.
In addition, the establishment and completion
of the operator's integrated service access point
(Point of Presence) achieves the unified access and
convergence of mobile services, fixed services, and
dedicated line services. With the virtualization of the
CU, MEC, OLT, CDN and other network elements, the
future PoP will evolve into a mini DC.
Future MAN traffic will be the north-south flows from
edge DCs to PoPs, and the east-west flows between
edge DCs and between PoPs. The backhaul networks
in the 5G stage will also be the DC interconnection
networks carrying all types of services. All levels of
DCs can be interconnected at high rates with OTN.
Optical networks build bandwidth resource pools,
configure and adjust bandwidth according to the
required traffic between DCs.
11
Figure 8
Backhaul Networks in the 5G Stage Will Be the DC Interconnection Networks Carrying Fixed Services and Mobile Services.
A 5G backhaul network can be achieved through the
collaboration between an IP network and an optical
network. IP networks and optical networks are the
most basic infrastructure of future bearer networks.
The heavy traffic of IP services between routers are
directly connected through optical layer channels,
reducing the number of intermediate routing
hops and the network latency and improving the
throughput of routers. The collaboration between
IP network and optical network achieves multi-
layer protection and recovery and enhances service
security. With the IP+optical synergy solution, the
flexible service forwarding capabilities of routers
and the large-capacity and low-latency transmission
capabilities of optical networks can be maximized.
5G backhaul networks can also be achieved based
on E-OTN. The packet enhanced OTN can achieve
not only service convergence and flexible service
forwarding on L2 and L3, but also large-capacity
and low-latency service transmission on L0 and L1.
Because integrated transmission equipment is used,
the network construction and maintenance cost is the
lowest.
12
Figure 9 OTN Solutions for Backhaul Network
The topology of backhaul networks is complex, and
OTN node equipment uses optical cross-connect and
electrical cross-connect for optical-electrical hybrid
scheduling, which is the best way to meet high-
speed transmission, flexible scheduling, and diversity
networking. Large-granularity services are scheduled
on the optical layer, while small- and medium-
granularity services are scheduled on the electrical
layer. With optical-electrical hybrid scheduling, the
overall power consumption to capacity ratio is the
lowest. Networks can be hierarchically constructed.
Ring networks are the main network topology on the
convergence layer. The single-wave rate on the line
side reaches 100 Gbps or higher, using 4-dimensional
mini ROADM and 10T electrical cross-connects. Mesh
networks are the main network topology on the
core layer. The single-wave rate on the line side can
be beyond 100 Gbps, using 9-dimensional to 20-
dimensional ROADM and large-capacity electrical
cross-connects. Based on the intelligent control
13
plane, end-to-end service deployment, dynamic
path calculation, auto adjustment of network
resources, and protection and restoration against
multiple failures are achieved. This not only meets the
bandwidth requirements of service development, but
also ensures the flexibility of service scheduling and
network reliability.
Figure 10 E-OTN Node Implements L0/L1/L2/L3 Unified Scheduling
SDN-Based Optical Networks Effectively Support the
Slicing and Intelligent Operation of 5G Networks
5G network slicing is implemented from end to end,
including wireless access networks, core networks,
and bearer networks. The OTN transmission plane
can implement slicing not only in hard pipes such as
wavelengths, ODU, and VCs but also in packet soft
pipes. As a part of the bearer network, the OTN based
on the SDN can configure and adjust bandwidth on
demand, use OVPN and other applications. Fast service
provisioning can be achieved in cross-domain and
cross-vendor large scale network to reduce operating
manpower, IP+optical synergy can be implemented
to reduce network construction and operating costs,
14
and interconnection bandwidth between DCs can be automatically scheduled. These have made preparations
for the future integration in the network architecture, the support for end-to-end 5G network slicing, and
intelligent operation.
Figure 11 Software Defined Optical Networks Effectively Support the Slicing and Intelligent Operation of 5G Networks
OTN Key Technologies in 5G Bearer Network
5G services require high bandwidth and high-speed
transmission. In a MAN with complex topology, using
the OTN equipment with the optical-electrical hybrid
scheduling capability for networking is the ideal
way. The ROADM optical cross-connect technology,
together with the OTN electrical cross-connect
technology, can provide larger cross-connect capacity
and more flexible scheduling capability, while
reducing system costs, power consumption, and space
occupation. Optical-electrical hybrid cross-connects
introduced in the MAN core and convergence layer
can achieve service convergence on the electrical
layer and service scheduling on the optical layer.
Using the optical-electrical hybrid scheduling in
mesh network can achieve multi-path access, reduce
the number of network layers and achieve flatten
network, reduce the service forwarding latency, and
improves network security.
1.Large-Capacity Optical-electrical Hybrid Scheduling
Fast service provisioning
E2E service management
in large scale network
Better tenant experience
Less maintenance task
Fully utilize network
resource
Release work load of
router
Reduce latency
Minimize cost of network
Support network
cloudization
Dynamic flow volume &
direction
Automation
15
2.Low-Latency Transmission and Forwarding
The latency introduced by OTN equipment is much
lower than that of other technologies, but 5G
fronthaul networks have very strict requirements
for the latency. The total latency of fibers and
transmission equipment in the level-1 fronthaul
must be shorter than 50 us. For the level-2 fronthaul
and backhaul , the shorter the latency the better.
The latency introduced by OTN equipment need to
be reduced from tens of microseconds to less than
than 10 us. ZTE optimizes the internal mapping
and multiplexing processing, forwarding mechanism,
interfaces, and other aspects of OTN equipment. With the
measures such as the reduction of cache time, automatic
adjustment of cache depth, changing serial processing
to parallel processing, increasing the internal processing
clock frequency, optimization of FEC processing
and optical modules, the latency of OTN equipment
introduction can be reduced to the microseconds level, to
better support new types of services
3.OTN Lite Standard for Fronthaul
For 5G fronthaul, the industry is also studying the new
lightweight OTN standard to reduce equipment costs,
reduce the latency, and achieve flexible bandwidth
configuration. For example, the OTN frame structure
can be optimized, n*25 Gbps interfaces may be used on
the line side, and low cost optical components can be
introduced. The error detection and correction mechanism
is changed so that the cache time can be reduced.
Fronthaul networks are simple topology in most cases,
so OTN overhead can be simplified to reduce equipment
processing steps. The innovative frame structure should
be compatible with CPRI used in 3G/4G fronthaul, eCPRI
and NGFI in 5G fronthaul, and small cell backhaul.
4.High-Precision Time Synchronization
To meet the high-precision time synchronization
requirements of 5G, ZTE's OTN equipment adopts 1588V2
specification, and implements phase detection and
synchronization on the basis of frequency synchronization
optimization. In addition, timestamp accuracy is
improved by modifying the triggering mechanism. Time
source selection and time synchronization algorithm
are optimized. Single-fiber bidirectional transmission
is used to eliminate latency asymmetry. Through
the comprehensive use of these technologies, time
synchronization accuracy is greatly improved.
5.Lossless and Low-Latency Protection Switching
Traditional protection switching is triggered by LOS, LOF,
and error over-threshold. When protection switching
occurs, the data stream is interrupted, the switching time
is short (< 50 ms), and most services are not affected.
However, some high-reliability services may be affected
in the future 5G. ZTE is studying the lossless and short-
latency protection switching mechanism, the error rate
after the correction of the data blocks is used as the
reference to select the optimal data block. The data
stream is not interrupted when protection switching
16
DCL4~L7
IPL2 / L3
OpticalL0 / L1 / L2
occurs. This mechanism is suitable for the mission-critical
service scenarios in the future.
6.Software-Defined Optical Network (SDON)
The programmable features of optical networks are
fully used to achieve SDN-based optical networks. ZTE’s
5G can bring more diverse services and better business
experience to people's work and life. 5G networks
need to be based on bearer networks, and have put
forward higher requirements for bearer networks. As a
basic bearer technology, OTN provides high bandwidth,
short latency, flexible slicing, high reliability, open
and coordination capabilities. It is suitable for mobile
SDON research and development focus on efficient
and intelligent routing computing capabilities, open
northbound and southbound interfaces, cross-layer and
cross-domain collaboration, integration of management
and control, secure and scalable controller software
platforms and hardware platforms.
Summaryfronthaul and backhaul in the new 5G network
architecture, it can also support the development of the
operator's fixed network services and other services,
meeting the continuous evolution of future networks.
The combination of optical networks and wireless
networks will create a ultrafast and extreme Internet of
Everything.
Figure 12 Overall Architecture of the OTN Solution for 5G Bearer Network
17
Acronym Full name in English
eMBB Enhanced Mobile Broadband
uRLLCUltra Reliable Low latency
Communication
mMTCMassive Machine Type of
Communication
MIMO Multiple Input Multiple Output
QAM Quadrature Amplitude Modulation
LTE Long Term Evolution
C-RAN
Centralized Processing,
Collaborative Radio, Cloudization,
Clean Radio Access Network
WDM Wavelength Division Multiplexing
OTN Optical Transport Network
PON Passive Optical Network
BBU Base Band Unit
RRU Radio Remote Unit
TDM Time Division Multiplexing
CPRI Common Public Radio Interface
eCPRI Enhanced CPRI
NGFINext Generation Fronthaul
Interface
CU Centralized Unit
Appendix
Acronym Full name in English
DU Distributed Unit
AAU Active Antenna Unit
ODUflex Flexible Optical Data Unit
CO Central Office
vEPC Virtualized Evolved Packet Core
vBNGVirtualized Broadband Network
Gateway
vCDNVirtualized Content Distribution
Network
vCPEVirtualized Customer Premier
Equipment
SDN Software Defined Network
NFV Network Function Virtualization
MEC Mobile Edge Computing
PoP Point of Presence
ROADMReconfigurable Optical Add Drop
Multiplexing
LOS Loss of Signal
LOF Loss of Frame
PLL Phase Locked Loop
BoD Bandwidth on Demand
OVPN Optical Virtual Private Network
SDON Software Defined Optical Network
top related