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

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© 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.