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EVOLVING MOBILE BACKHAUL TO SUPPORT LTE-A AND BEYOND
MOBILE BACKHAUL 2.0
APPLICATION NOTE
We all know from our own experience how quickly wireless networks
are evolving. If we stop to think for a moment and remember
the phone we had 2, 5 or 10 years ago and the capabilities and
functionality these devices had, then it quickly becomes apparent
how rapidly this industry is changing.
Advances in handset and radio access network (RAN) technology are
underpinned by significant advances in mobile backhaul technology
that may not be apparent to the user.
A few years ago, the backhaul industry transformed from a
predominantly T1/E1 time division multiplexing (TDM) based network
to an Ethernet network to support the higher bandwidth and better
cost-per-bit economics required to support the explosive growth
in mobile data.
Now these same networks need to transition again to support
significantly better transport performance to support the evolution
to long term evolution (LTE)-Advanced (LTE-A) functionality, while
improving cost-per-bit performance.
This application note addresses the next generation of mobile
backhaul networks that support backhaul of any cell from pico
to macro and from any location, the cell itself, a baseband unit
(BBU) hotel or a fibered up aggregation point where micro/
millimeter-wave solutions are used for the last mile.
Infinera also provides a wide range of mobile fronthaul
solutions that complete the offering and enable operators
to support any fiber based transport for mobile networks
from the same platform and network nodes. These fronthaul
solutions and the specific challenges of mobile fronthaul that
these address are described in a separate application note.
2
Network Evolution
Transport networks that support mobile/wireless operators are
undergoing three major transitions at the same time.
First, macrocell is becoming a range of pico/femto/micro/macro cells
that will often work together in a heterogeneous network (HetNet)
that comprises of a mix of these cell types. These cells now overlap
considerably more than previously and will use a range of last mile
access technologies to take advantage of fiber where possible and
to use new wireless backhaul technology where this isn’t possible.
Mobile Fronthaul and C-RAN Networks
In parallel to the above, network operators are now evaluating and in
some cases starting to deploy, mobile fronthaul networks to support
centralized-RAN (radio access network) and ultimately cloud-RAN
(both simplified to C-RAN) networks where the baseband unit (BBU)
moves from the cell site to a central BBU-hotel location. This creates
a new fronthaul network between the BBU and the cell site based
on the common public radio interface (CPRI) or open base station
architecture initiative (OBSAI) protocols that are effectively digitized
radio frequency (RF) signals.
All these networks require fiber based backhaul of Ethernet traffic
from either the cell site or the BBU location regardless of the last
mile technology. The last mile could be the same Ethernet over fiber
connection, Ethernet over some other media such as copper or
microwave or mobile fronthaul. The requirements for the end point
of the backhaul service change as the cell changes from a traditional
macro cell to a smaller cell, typically with more stringent requirements
to meet environmental specifications, such as temperature range
support, space and power but this is still an Ethernet over fiber
backhaul connection.
Evolving Backhaul to Mobile Backhaul 2.0
As wireless networks evolve to support LTE-A features such as
enhanced inter-cell interference coordination (eICIC) and coordinated
multipoint (CoMP) then the underlying transport network typically
must undergo a step change in performance to support considerably
tighter requirements in terms for transport performance – specifically
in the areas of both frequency and phase synchronization and latency
performance.
Historically, mobile networks required good quality frequency
synchronization, but now as these new features and capabilities are
added, then the specification for frequency synchronization remains
important and cells also need phase synchronization and time-of-
day timestamps.
As the performance of these backhaul networks is now even more
important than before, then performance monitoring capabilities
become important to ensure the service level agreement (SLA) is
met. This applies both internally within network operators and also
in the wholesale scenario where a third party operator provides all
or some of the backhaul connection.
Overall, next generation mobile backhaul solutions intended to
support LTE-A needs provide outstanding transport performance and
also maintain or enhance the cost-per-bit economics of the network.
Building on the Native Packet Optical 2.0 Architecture
The mobile backhaul solution from Infinera is built around the
company’s Native Packet Optical 2.0 architecture and provides a
very good platform for today’s networks. The architecture combines
Layer 2 Ethernet and Layer 2.5 multiprotocol label switching-transport
profile (MPLS-TP) technology with Layer 1 wavelength division
multiplexing (WDM) technology in a transport focused architecture.
This approach gives very good performance around key transport
parameters, such as latency performance and synchronous Ethernet
(SyncE) performance for frequency synchronization that is an order of
magnitude better than the time division multiplexing (TDM) based
synchronization that was previously used in mobile backhaul.
From a services perspective, the solution is Metro Ethernet Forum
(MEF) Carrier Ethernet 2.0 (CE2.0) certified providing operators with
a broad range of standard service options that are interoperable with
other networks. These are backed by a high level of resilience within
the network through technologies
such as Ethernet Ring Protection
version 2 (ERPv2) and multi-chassis
link aggregation group (LAG) and
even ERP over LAG options.
In addition to such resiliency, all services have high quality SyncE
by default. Key to delivering these services in mobile networks is
operational simplicity which is delivered through the Infinera Transport
Network Manager (TNM).
TNM offers service aware network management with integrated
operational and administration management (OAM) capabilities,
and a scalable pay-as-you-grow (PAYG) licensing model.
The Native Packet Optical 2.0 architecture also provides a low power
and dense solution which further enhances the economics.
MOBILE BACKHAUL 2.0
3
Carrier Ethernet 2.0 – Key to Service Delivery
MEF has defined eight different service types within the CE2.0
certification program and the Infinera Mobile Backhaul 2.0 solution
fully supports all eight giving the operator a wide range of service
options. These service types extend the original carrier Ethernet (CE)
services to include capabilities such as support for multiple classes
of service (CoS), each with varying levels of quality of service (QoS).
This is particularly of interest to mobile operators moving to LTE and
LTE-A as this enables the support of the different levels of priority
traffic supported in the LTE specifications, such as high priority for
steaming video and signaling traffic and lower priority for less time
dependent traffic such as web browsing.
1 Restricted
BSC MME RNC
eNB
Service GW / MME
E-Access
eNB eNB
UNI UNI UNI UNI
UNI
NNI NNI
E-LAN / E-Tree E-Line
Core
UNI
Fig 1. The Infinera Mobile Backhaul 2.0 Solution Fully Supports the CE2.0 Services.
The new CE2.0 service definitions also add a new network to network
interface (NNI) to a user network interface (UNI) service an E-Access
service. This, and CE2.0 services in general, is ideal for local access
connections, which are often found in mobile networks in which the
last mile being provided by a wholesale operator.
The Importance of Low Latency
Controlling latency has become increasingly important as mobile
networks migrate from LTE to LTE-A and eventually to 5 Gb/s.
In the days of TDM based mobile backhaul, latency was relatively
fixed based on the fiber/copper delays and hardware delays that
were reasonably constant. As backhaul moved to Ethernet, however,
hardware complexity has increased, with the potential for higher
latency if this isn’t managed carefully. Also, due to the nature of
Layer 2 Ethernet hardware, then the variation in latency through the
hardware also becomes a significant factor, which is known as jitter.
The Infinera Native Packet Optical 2.0 architecture is built on a family
of packet optical transport switches (EMXP) devices. These have
an output-buffer queued switch architecture which has the effect
of providing a very low and almost
fixed latency, providing low latency
at around 2 microseconds per node
and near zero jitter (latency variation
over time).
This transport like performance for a packet-optical network provides
an excellent base for good 1588v2 phase synchronization messages. It
is also extremely important as networks migrate to LTE-A and beyond
as these introduce new features such as coordinated multi-point
(CoMP) and enhanced inter-cell interference coordination (eICIC)
where signaling between cells is essential. These features require
low latency backhaul connections and low latency X2 interface traffic
to ensure correct signaling and control.
Mobile Packet Core
X2 fast
X2 slow
Two deployment scenarios for X2; Fast and Slow
Fig 2. The Low Latency in the Mobile Backhaul 2.0 Solution Makes It Ideal for Transporting the x2 Signaling, Which Is Used in LTE Networks.
Controlling Additional Costs
Beyond the economics of the backhaul hardware, it is important to
consider the additional ongoing running costs of any mobile backhaul
network. Space and electrical power are expensive and often a scarce
resource in these networks.
To address this, the Mobile Backhaul 2.0 solution provides a highly
dense solution with industry-leading low power credentials. The
solution scales from compact CPE nodes to large nodes that would
support aggregation and transport nodes deeper in the network.
On the next page you’ll find an example configuration of a Mobile
Backhaul 2.0 node.
MOBILE BACKHAUL 2.0
4
Mobile Backhaul 2.0 Example Configuration
The TM-3000 chassis is typically used in this configuration and can support a compact packet-optical configuration with 88x GbE and 16x 10 Gb/s Ethernet (via 4x EMXP units with 4x 10 Gb/s and 22x GbE each) plus all necessary optical layer units such as filter, amplifier, variable optical attenuator (VOA) and optical channel monitor (OCM) for full operation including automated power balancing.
This example configuration has spare slots for growth and only draws 400 watts of power for the complete node.
Managing It All in the Enlighten® Multi-layer Management Suite
As noted above, service OAM is a key component in the mobile
backhaul solution enabling operators to fully manage all aspects
of the backhaul service through its lifetime. Service OAM allows
operators to control and manage services at service activation to
ensure the service is up and running as expected.
Once the service is in-service then the operator can monitor key
service parameters, such as Y.1731 loss measurements for user traffic,
sent/received frames, and the frame loss ratio. 2-way delay and 2-way
delay variation may also be monitored using the Y.1731 standard.
Further, service availability can be monitored via the MEF 35 standard
with measurements of the number of unavailable seconds and high
loss intervals.
These measurements are available via the TNM and the Enlighten
Portal. The Portal allows approved network engineers quick access
to network performance data or allows wholesale operators to prove
this data to end customers, in this case mobile operators.
Monitoring data may be graphically displayed on a laptop or handheld
device, such as a smartphone, to provide users with a simple, high-
level view and can drill down to detailed data if needed.
One important aspect of this functionality is that it is available on all
services within an Infinera Mobile Backhaul 2.0 network regardless
of the node type that terminates the service.
One Single Management Suite for Multi-layer Mobile Transport Networks
The Enlighten multi-layer management suite supports the entire
lifecycle of any Infinera network and is ideal in networks that support
multiple applications and multiple layers of the network. Mobile
transport is a good example where the suite supports Layer 2 based
mobile backhaul and Layer 1 based mobile fronthaul seamlessly.
Enlighten provides tools to support planning, deployment and
operational stages of a network or service and is field proven with
both small, simple networks and large multi-layer networks with
thousands of network elements.
A key feature of mobile networks
is the service template feature.
This is useful in networks such as
mobile backhaul networks where
hundreds or thousands of services
need to be created with the same
or similar service parameters.
Service templates can speed up
service creation to as little as 20 seconds and can also reduce the
risk of errors in the service parameters.
Synchronization is critically important in mobile networks and this
includes sync management capabilities, which the Enlighten suite
provides.
Mobile Backhaul 2.0 – It’s Packet-optical in Action
Mobile backhaul is an excellent example of packet-optical in action
as it enables the step change required from old TDM based backhaul
to higher performance, lower cost and much greater scalability.
Modern packet-optical solutions enable the IP traffic between cell
site gateways and core routers to be optimized and avoid unnecessary
router hops.
As discussed above, the solution supports Ethernet transport for all
cell types and all locations regardless of last mile technology – CPRI
based fronthaul, distributed antenna systems (DAS), fiber connected
small or macro cells or fiber aggregation points supporting microwave
backhaul for non-fiber environments.
MOBILE BACKHAUL 2.0
5
Moving Mobile Backhaul 2.0 – Adding Superior Synchronization
The previous Infinera mobile backhaul solution is widely deployed in
mobile networks providing high quality SyncE based Gigabit Ethernet
transport. Infinera is building on this solid base and now extending
the synchronization capabilities further to support the additional
synchronization requirements required for LTE-A and beyond.
The LTE specifications allow two basic modes of operation:
• Frequency division duplex (FDD) where communications channels
use different frequencies
• Time division duplex (TDD) where a frequency is shared and
individual timeslots are used per communication channel
The move to TDD changes the network synchronization requirements
from simple frequency synchronization using methods such as SyncE or
1588v2 packet based synchronization for frequency only, to a network
that needs to also understand the phase of the synchronization signal
and to also receive accurate time-of-day timestamps. This is commonly
referred to as phase synchronization.
Also the more complex LTE-A features such as coordinated
multipoint (CoMP) transmission and reception and enhanced inter-cell
interference coordination (eICIC) mandated phase synchronization.
Different mobile technologies and applications require differing level
of frequency and phase synchronization accuracy as shown in Table
1 to the right.
Superior sync is one of the key
cornerstones of the Infinera Mobile
Backhaul 2.0 solution.
Table 1. Frequency and Phase Synchronization Requirements.
As networks move to LTE (TDD) and LTE-A then they need frequency
with the same quality as previous generations of mobile networks
and also stable phase synchronization.
Frequency synchronization can be delivered using a variety of
methods but it is commonly delivered over the network using SyncE
technology. Frequency synchronization may also be provided locally
using a global navigation satellite system (GNSS) method, such as
global positioning system (GPS) in some regions of the world. Those
regions that do use GNSS/GPS may also use the network as a backup
in the case of failure or jamming.
Phase synchronization is delivered using 1588v2 precision timing
protocol (PTP). There are a number of ways in which the network
performance can assist the quality of the resulting PTP within the base
station. First, using network elements with low jitter has a positive
impact on the quality of the received PTP by reducing errors.
MOBILE BACKHAUL 2.0
Fig 3. Mobile Backhaul 2.0 Is Agnostic to Last Mile Technology Used.
Application Frequency PhaseGSM/UMTS/W-CDMA 16 ppb / 50 ppb None
UMTS / W-CDMA Femtocells n/a / 250 ppb None
CDMA2000 16 / 50 ppb ± 3 to 10 µs
TD-SCDMA 16 / 50 ppb ± 1.5 µs
LTE (FDD) 16 / 50 ppb None
LTE (TDD) 16 / 50 ppb ± 1.5 µs
LTE-A MBSFN 16 / 50 ppb ± 1.5 to 32 µs
LTE-A eICIC 16 / 50 ppb ± 1.5 to 5 µs
LTE-A CoMP (Network MIMO)
16 / 50 ppb ± 1.5 µsto ± 500 ns
6
Secondly, by supporting SyncE and 1588v2, the network is able to
operate in a hybrid mode, allowing the SyncE to assist the 1588v2
protocol and provide a better overall result. In addition, the network
can provide 1588 onpath support to again provide a better quality
result.
Poor synchronization has a negative impact on network performance
and results in a less efficient radio interface, poor performance for
data traffic and dropped calls.
Network operators spend considerable time and money on achieving
good synchronization at all cell sites and a mobile backhaul network
with the best possible synchronization support can produce savings in
both of these areas. Moreover, as mobile networks evolve to support
5 Gb/s standards then the synchronizations requirements will get
tighter and better synchronization performance today will enable
networks to support these future requirements too.
The Infinera Range of Mobile Backhaul 2.0 Synchronization Options
To enable mobile operators and wholesale operators who support
them with last mile access connections to best support the new
tighter LTE-A synchronization requirements, the Mobile Backhaul
2.0 solution now offer 3 options to support phase synchronization:
• In addition to using SyncE for frequency synchronization, SyncE can
be used in a hybrid “SyncE assist” mode which gives significantly
better 1588v2 phase synchronization performance.
• Full onpath support using 1588 transparent clock
• Partial onpath support using 1588 boundary clock
SyncE Assist
The Infinera range of EMXP units support SyncE with industry-leading
performance which is an order of magnitude or more better than
the TDM based synchronization used in the previous generation
of mobile backhaul networks. This can be used in a hybrid mode
to support 1588v2 phase synchronization within mobile backhaul
networks to greatly improve phase performance.
Getting 1588v2 phase synchronization to work in real-world mobile
backhaul networks can be difficult to scale up in larger networks. It
can be a real challenge to meet the 1.1 microsecond requirement
for mobile backhaul, which is the budget allowed within the total
1.5 microsecond total end-to-end budget.
Using SyncE within the mobile backhaul network can significantly
improve on the eNodeB 1588v2 phase synchronization performance
as shown in Figure 4 to the right.
Fig 4. Slave Clock Error for 1588v2 with and without SyncE Assist.
Adding 1588v2 T-TC Phase Support to All Nodes
Transport of 1588v2 can be further improved by providing telecoms
transparent clock (T-TC) support to the mobile backhaul network.
Rather than simply passing the 1588v2 packets through a node as
normal data packets, this mode of operation detects the 1588v2
packets and adjusts the time stamp in the 1588v2 packets to correctly
reflect the latency added by the node to the packet flow. As a result,
the slave clock at the cell site receives a more accurate timestamp
within the 1588v2 packets, and, therefore, provides better phase
synchronization to the cell site. This mode of operation is a simple on/
off configuration requiring no complex configuration and interworks
simply with other third party systems.
When the T-TC capabilities are enabled, a node will apply real-time
correction to each 1588v2 packet to compensate for the delay added
by the node. As each packet is corrected separately, the method
handles traffic asymmetry as the flows in each direction are corrected
independently. This is important as the 1588v2 protocol relies on
calculating the total round trip delay across the network and this
calculation can be hampered by asymmetrical delays across a network
due to different delays in the go and return routes. This can be due
to the go/return paths being routed differently or differing delays
across individual nodes in each direction.
Avoiding selecting differing go/return routes can be handled in the
management system and T-TC then handles any asymmetry within
nodes leading to improved 1588v2 performance.
MOBILE BACKHAUL 2.0
7
1588v2 T-TC advantageously reduces the packet delay variation
(PDV) experienced by the eNodeB slave clock. For example a fully
loaded mobile backhaul network with 10 Gb/s links of 10 hops may
have a PDV on the order of 16 microseconds, even if constructed
from high quality network elements because each node adds to the
PDV across the network.
The eNodeB slave clock will not be able to maintain time and
phase synchronization required by LTE-A, which leads to the phase
synchronization running off exponentially as the PDV increases.
In a ten hop network, for example, adding 1588 T-TC to the Mobile
Backhaul network will bring the PDV experienced by the eNodeB
down from 16 microseconds to 200 nanoseconds. This allows the
resulting phase synchronization error to go from well outside the
required 1.1 microsecond requirement, to around 80 nanoseconds,
which is well within the requirement.
Fig 5. Measurement of Packet Delay Variation (PDV) Without and With T-TC Showing the Significantly Reduced PDV that the T-TC Onpath Support Provides.
All of the Infinera Enhanced EMXP (EMXP IIe) support T-TC
functionality.
Bridging Non-T-TC or SyncE Assist Islands with T-BC
1588v2 T-TC and SyncE assist mode can improve phase performance.
However, mobile backhaul networks are not always built using nodes
that support either hybrid SyncE Assist mode or 1588 T-TC in every
network element, and new nodes may need to interact with legacy
nodes from multiple vendors.
To support these environments, Infinera is adding 1588v2 telecom
boundary clock (T-BC) capabilities to the Mobile Backhaul 2.0 solution.
This allows the network to realign the clock and compensate for the
wander that builds up in the network.
Using the same ten hop network as an example in which every third
node is a T-BC nodeallows the network to absorb errors introduced
by non-supporting nodes so that the final clock is within required
specifications.
8 Restricted
T-BC
T-BC
T-BC
GM T-SC
PLL absorbing wander PLL absorbing wander PLL absorbing wander Acceptable wander
10G 10G 10G 10G 10G 10G 10G 10G 10G
GbE GbE GbE GbE GbE GbE GbE GbE GbE GbE
Performance Monitoring
Correlating Asymmetry
Fig 6. The Infinera T-BC Implementation Reduces Wander Significantly.
MOBILE BACKHAUL 2.0
Global Headquarters 140 Caspian Court Sunnyvale, CA 94089 USA Tel: 1 408 572 5200 Fax: 1 408 572 5454 www.infinera.com
US Sales Contacts [email protected]
Asia and Pacific Rim Infinera Asia Limited 8th floor Samsung Hub 3 Church Street Singapore 049483 Tel: +65 6408 3320 [email protected]
Europe, Middle East, Africa Infinera Limited 125 Finsbury PavementLondon EC2A 1NQ, United KingdomTel: +44 207 065 1340 [email protected]
Customer Service and Technical Support North America Tel: 877 INF 5288 Outside North America Tel: 1 408 572 5288 [email protected]
© 2016 Infinera Corporation. All rights reserved. Infinera and logos that contain Infinera are trademarks or registered trademarks of Infinera Corporation in the United States and other countries. Enlighten is a trademark or registered trademark of Transmode Systems AB in the United States and other countries. All other trademarks are the property of their respective owners. Infinera specifications, offered customer services, and operating features are subject to change without notice. AN-Mobile-Backhaul-2.0-04-2016
A B O U T I N F I N E R A
Infinera (NASDAQ: INFN) provides Intelligent Transport Networks,
enabling carriers, cloud operators, governments and enterprises to scale
network bandwidth, accelerate service innovation and simplify optical
network operations. Infinera’s end-to-end packet-optical portfolio is
designed for long-haul, subsea, datacenter interconnect and metro
applications. Infinera’s unique large scale photonic integrated circuits
enable innovative optical networking solutions for the most demanding
networks. To learn more about Infinera visit www.infinera.com, follow us
on Twitter@Infinera and read our latest blog posts at blog.infinera.com.
MOBILE BACKHAUL 2.0
Bringing It All Together in Mobile Backhaul 2.0
As we move from today’s mobile environment to the network of the
future, networks will evolve to support more stringent requirements
in mobile backhaul to support the new network capabilities. Infinera’s
Mobile Backhaul 2.0 solution builds on low latency SyncE with
new 1588v2 capabilities including hybrid 1588v2/SyncE, 1588v2
transparent clock, and 1588v2 boundary clock options. The solution
gives industry leading low power and high density capabilities with
a powerful multi-layer management suite.
Networks built today need to support a variety of mobile
environments including mobile fronthaul and mobile backhaul in
HetNet environments and the Infinera mobile backhaul 2.0 and mobile
fronthaul solutions are unique in their high performance and range
of network architecture capabilities.