i Pmp Ls Mobile Back Haul White Paper

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WHITE PAPER

Use of MPLS technologyin mobile backhaul networks

Introduction

Backhaul plays a vital role in mobile networks by acting as the link between Radio Access

Network (RAN) equipment (Eg: radio basestation) and the mobile backbone network. This

means that backhaul is able to transport mobile data from the end user to the internet (or

similar network), mobile networks and traditional telephone networks.

The rapidly evolving telecoms marketplace has meant that mobile operators are facing a

significant spike in bandwidth demands in the backhaul due to the proliferation of 3G-based

data services and the emergence of high-speed air interface enhancements such as High

Speed Packet Access (HSPA).

At the same time, backhaul network operators are being required to significantly reduce opera-

tional costs in order to compensate for declining Average Revenue Per User (ARPU) and to com-

pete with a host of new competitors and technologies. Operators are also required to protect

(or sufficiently emulate) core legacy services such as voice, which still account for a substantial

share of revenue.

In this new situation backhaul networks with many cell sites have become the bottleneck

offering insufficient capacity to support higher bandwidths and often expensive to upgrade.

To address the problem operators are migrating from existing separate, legacy ATM and TDM

backhauling networks to a more cost-effective, converged, MPLS-enabled, and multi-purpose

infrastructure. In addition to reducing operational costs, MPLS-based networks will also lay the

foundations for the delivery of next generation mobile services, such as location-based services,

mobile gaming and mobile TV, and for the use of future technologies such as Long TermEvolution (LTE) and mobile WiMAX.

Ultimately, this fully consolidated network will be able to handle many different types of traffic

on a single cell site, enabling the operator to offer many different services to many different

types of customer.

The IP/MPLS Forum is tackling these backhaul challenges via its MPLS Mobile Backhaul Initiative

(MMBI). The initiative aims to leverage the benefits of MPLS technology in the backhaul by

providing a framework for a single MPLS aggregation/backhaul network that is flexible, scalable

and economical.

This White Paper outlines the market dynamics that are driving the need to deploy MPLS

technology in Radio Access Network (RAN) backhaul and provides a brief overview of the MMBI.

February 2008

CONTENTS:

Introduction ..............

Market Trends

and Challenges .........

Overview of

IP/MPLS Forums

MPLS Mobile

Backhaul Initiative ....

Business Benefits

of IP/MPLS Forums

Mobile Backhaul

Initiative ....................

Architectural

Overview...................

RAN Equipment

Synchronization........

OAM and

Resiliency...................

Conclusion.................

1IP/MPLS Forum White Paper


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Third-generation mobile networks have become a reality. By

November 2007 there were 190 3G networks in commercial

service across 83 countries worldwide with over 800 different

types of 3G devices launched into the market available

from around 90 suppliers (source: Global Mobile Suppliers

Association. Dec 2007). There was forecast to be 252 million

3G subscribers worldwide by December 2007 (source: Informa

Telecoms & Media: Sept 2007).

This trend allows mobile operators to generate revenues

from a range of new next generation data services that

are designed to generate revenues in addition to those from

legacy voice services.

However, these new 3G-based services will also require a

substantial increase in bandwidth, which will in turn lead to

greater mobile backhaul costs. It is estimated that backhaul

can account for as much as 30% of a mobile operators

operating costs (Opex) (source: Yankee Group, 2005).

If mobile operators were to expand the backhaul network

to meet these new bandwidth requirements in the traditional

manner the move to 3G could represent a significant increase

in required bandwidth and associated opex.

The cost of backhaul is not the only consideration in the

migration to 3G. As well as extra traffic, backhaul will need

to be able to handle a range of new functionality, including

Quality of Service (QoS) and resiliency management. These

new elements will become increasingly important as mobile

operators migrate towards packet-based backhaul networks.

Mobile operators will also be required to protect existinglegacy technology investments for some years. At the same

time operators will need a backhaul strategy that is future-

proof and will be able to support a new generation of

networks and access technologies such as LTE. This requires

the mobile backhaul network to support many different

generations of technologies simultaneously.

The access and aggregation networks are used for more than

just mobile backhaul and it increasingly being used to carry

traffic for more than one mobile operator. This requires meth-

ods of separating and securing multiple operator traffic while

maintaining service level agreements. We estimate that as

many as three-quarters of 2G and 3G cell sites are co-located.

The access and aggregation networks can be used to hostmultiple services as well as multiple operators. For example,

an ISP that has an IP/MPLS based network could provide

services such as IPTV, broadband access and enterprise VPN

as well as mobile backhaul services, generating further value

from the network.

The new backhaul infrastructure must therefore meet three

main criteria: it must be flexible (to support both legacy and IP

services), scalable (to support emerging future technologies)

and cost-effective (to compensate for rising levels of backhaul

traffic). It also needs to be a converged network, which means

the operator does not need to run two separate networks(leased lines and IP).

These market trends have made backhaul a strategic asset

for mobile operators and one that is currently a major area

of investment; these trends will grow as further air interface

enhancements (HSPA, EV-DO, Rev C, mobile WiMAX etc.)

are rolled-out. However, global ARPU trends remain only flat

or negative, despite an uplift in the proportion of revenues

relating to higher-bandwidth data services. This creates a

major business challenge with backhaul as a significant

bottleneck (see figure 1).

A study by Infonetics Research suggested that the globalmarket for backhaul equipment grew to $3.5 billion in

2007 and is forecast to grow to $5.6 billion by 2010,

including legacy emulation services. (source: Mobile

Backhaul Equipment, Installed Base, and Services,

Infonetics Research, 2007)

2 Use of MPLS technology in mobile backhaul networks

Voice Dominant

Traffic

Revenues

Data Dominant

Time

Quantity

Cellular operatorrevenue & traffic

decoupled

Market Trends and Challenges

Figure 1: ARPU declines; bandwidth increases


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Figure 2. Scope of MMBI

Overview of IP/MPLS Forums MPLS Mobile Backhaul Initiative

Backhaul TransportTransport network &Mobile Core Network

Core Network for2G,3G,LTE,

WiMAX

2G,3G,LTE,

WiMAX

RAN

IP/MPLS Forum Focus Area

for Backhaul

RNCBSCSAEAggregation

Network

AccessNetwork

AccessNetwork

TrafficGroomingatCellSite

TrafficGroomingatCellSite

The IP/MPLS Forums MPLS Mobile Backhaul Initiative (MMBI)

proposes a framework for the use of MPLS technology to bring

solutions to transport RAN backhaul traffic over access, aggre-

gation and core networks. The framework describes possible

deployment scenarios and provides recommendations on how

to deploy MPLS in each of these scenarios. This will create a

reference guide that will allow vendors and operators to select

the appropriate feature sets for their specific scenario.

The focus is on a shared network infrastructure that is able to

support (emulate) existing legacy services (2G, 2.5G) as well as

new services based on 3G and beyond (Eg: HSPA, LTE). This

will enable a migration path between existing legacy ATM and

TDM backhaul networks to a more cost-effective, converged,

MPLS-enabled, and multi-purpose network.

The work is independent from the air interface technology

wherever possible but allows for the possibility that some

specific backhaul requirements related to the air interface

may need to be considered.

Areas within the scope of the initiative include: QoS

considerations (Eg; to support specific service types), resilien

capabilities, clocking and synchronisation, Operations and

Maintenance (OAM), and support for various Transport

Network Layers (TNLs), LTE and mobile WiMAX.

Business Benefits of IP/MPLS Forums Mobile Backhaul Initiative

This combination of rising traffic requirements coupled with

declining revenues is a key motivation for operators migrating

RANs to a converged, packed-based architecture (see figure

1). MPLS has been globally deployed in these types of net-

works and has been an important element by creating an

environment for the delivery of new data services. As thesepacket-based networks grow in popularity, MPLS must now

also be extended into to the backhaul.

This architecture will directly impact mobile operators bottom

line by simplifying operations, reducing Opex and leveraging

the cost benefits of backhaul technologies such as Ethernet.

It will also enable operators to support next generation

services such as location-based services (LBS), mobile IPTV

and mobile gaming, and will be sufficiently flexible to protec

investments in new and emerging technologies.

This flexibility works in two ways: it will protect radio

equipment investment legacy 2G/3G and it will be able

to be re-used again as mobile operators migrate to futuretechnologies such as LTE and mobile WiMAX.

MPLS is an established technology with proven support for

providing QoS, traffic engineering (TE), legacy layer 1 and

layer 2 emulation (via pseudowires) and resiliency features.

These advantages can be leveraged for use in a wide variety

of network architectures and applications such as Enterprise

VPN, IPTV, mobile backhaul among others.


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In the legacy environment, RAN equipment communicates via

either TDM or ATM TNLs and are connected with a T1/E1

interface, or with an Ethernet interface (Fast Ethernet) if TDM

or ATM is encapsulated over Ethernet via IP or MPLS. The

functionality necessary to transport legacy traffic over MPLS

can be performed either at the edge node, the access node,

the access gateway or directly in the RAN equipment. The

HDLC layer features in CDMA 1x-RTT and covers RAN equip-

ment communicating by means of HDLC-encoded bit streams

Architectural Overview

Legacy

Network architectures for RAN backhaul in the IP/MPLS Forums MPLS Mobile Backhaul Initiative are defined for various

Transport Network Layers (TNL) and mobile network generations. These scenarios are grouped as follows and comprise two

basic categories: legacy (TDM, ATM, HDLC) and future (IP/Ethernet).

Network Specification TNL Speed (approximate)

GSM/GPRS (2G/2.5G) TDM 56 - 114 Kbps

EDGE (2.5G) TDM 236.8 Kbps 473.6 Kbps

UMTS /HSDPA/HSUPA R3, R99/R4 ATM ~384 Kbps (uplink)

(3G) R99/R5, R6 ATM ~ 2 to 3.1 Mbps (downlink)

IP

CDMA 1x-RTT (2.5G) IS-2000 HDLC or TDM 144 Kbps

CDMA 1x EV-DO (3G) IS-856 IP ~ 1.8 Mbps (uplink),

~ 3.1 Mbps

(downlink)

Mobile WiMAX WiMAX Forum IP 50 Mbps

Network Access

Architecture R1.1

Long Term Evolution (4G) R7/R8 IP > 50 Mbps (uplink)

> 100 Mbps (downlink)

The same flexibility that lets MPLS be applied to these various

applications allows it to be applied to legacy mobile backhaul

networks as well as future technologies such as LTE. For

example, the same MPLS network infrastructure can be used

to carry the legacy traffic pseudowires may also be used to

carry and provide QoS guarantees to next generation LTE

traffic. Additionally, MPLS can be deployed on any layer 2

technology capable of supporting MPLS labelled switching.

IP/MPLS - with its packet-switching advantages and

pseudowire technology - is ideally suited to overcome the

scalability limitations of traditional circuit based technologies

such as ATM and TDM. MPLS permits support of these tech-

nologies using pseudowires to protect existing investments in

legacy equipment. For future IP and Ethernet based interfaces,

it is possible to aggregate traffic over single TE tunnels and

provide differentiated services for this aggregate so that QoS

requirements are met while at the same time providing further

improvements in scalability.

Because a single service provider can leverage the MPLS

network to meet the requirements of not only the diverse

set of mobile backhaul technologies but also to those ofother applications, the MPLS network also provides economies

of scale. This has a significant impact in reducing both a

service providers capital and operational costs. Furthermore,

investments in MPLS technologies benefit the service provider

by making it future proof and still applicable in the fast

evolving mobile technology scenarios (eg: LTE and beyond).


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MobileCore

Network(s)

3: BackhaulTransport Reliability

1: Radio FramingAccuracy

2: Hand Off Control

Node

Node RN

ET

ETBSCBSC

5IP/MPLS Forum White Paper

Future

RAN Equipment Synchronization

Figure 3: Clocking and synchronisation in RAN

In R5 3G, LTE and mobile WiMAX environments, the RAN

equipment interfaces use the IP TNL either at the Iub inter-

face (for 3G) or on R7/R8 for LTE or mobile WIMAX. Mobile

traffic over IP TNL can be transported either via Ethernet

pseudowires or regular IP/MPLS TE tunnels over MMBIs

mobile backhaul network. IP termination can take place either

at the edge node, the access node, the access gateway or

directly at the RAN equipment.

Various deployment scenarios arise depending on the locatio

(and the extent) of MPLS technology in the mobile backhaul

network and whether it comprises both the access and aggre

gation sections of the network or just the aggregation sectio

For further details on the MMBI reference architecture

please visit: http://www.ipmplsforum.org/ or e-mail

[email protected]

RAN equipment needs to be fully synchronised to a common

reference timing signal to ensure sufficient frequency stability,

radio framing accuracy and handoff control for RF channels.

Thus the mobile backhaul network needs to support distribu-

tion of frequency from the Radio Network Controller (RNC) to

the RAN equipment.

For example, in the case where the air-interface is based on Tim

Division Duplexing (TDD), the base station clocks must be syn-

chronized to ensure no overlap of their transmissions within th

TDD frames. Ensuring synchronisation allows for tighter accura

cies and reduced guard bands thereby ensuring higher capacity

In the case of legacy TNLs such as TDM, synchronisation alsofocuses on backhaul transport reliability (see figure 3).


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The MMBI outlines the following methods for clock distribution

over an IP/MPLS based backhaul network. In the case of RAN

equipment with IP TNL (including LTE), packet based methods

where the frequency reference is carried over packets (e.g.,

based on Network Time Protocol (NTP)) may be used to deliver

frequency to address the frequency stability requirements of the

radio equipment. For legacy TNLs, such as TDM, and ATM, a

dedicated timing stream implemented using a pseudowire maybe used to carry the reference timing signal from the RNCs to

the RAN equipment both for backhaul transport reliability as

well as frequency stability requirements of the radio equipment.

Other methods for distributing the reference timing signal

to the RAN equipment include, delivery via methods such as

synchronous Ethernet or IEEE 1588 v2 or by deriving timing

from the PDH/SDH transmission mechanisms used in the

mobile access networks. In particular in order to support thestrict synchronization requirements of TDD systems, the use

of GPS is a widely used option.

One of the main advantages of MPLS is that it provides a wide

selection of flexible troubleshooting and OAM tools that enable

the deployment of a truly carrier-grade backhaul network.

These include fault detection methods to drive protection

switching mechanisms such as MPLS Fast Reroute. Other

protocols enable fault diagnosis, fault isolation (eg: LSP Ping

and LSP traceroute) and performance monitoring. MPLS

protocols also provide tools for loopback and connectivity

check. Examples include VCCV for pseudowire-based MPLS

backhaul solutions and BFD for IP based MPLS backhaul

solutions. These OAM tools will remain applicable for future

LTE mobile backhaul networks implemented as either IP

based or Ethernet pseudowire based solutions.

For legacy TNLs and Ethernet pseudowire based solutions,

the MMBI initiative leverages previous specifications by the

IP/MPLS forum that support interworking between native

Layer1/Layer2 OAM and MPLS OAM.

OAM and Resiliency


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Conclusion

The migration towards 3G networks and devices is expected to quick-

en over the next few years. Air interface enhancements such as HSPA,

a relatively inexpensive network upgrade, will also continue to grow in

popularity. Mobile operators have also begun to develop strategies and

technology roadmaps that will enable them to launch 4G services

using technologies such as LTE and mobile WiMAX. The first commer-

cial launches of these 4G networks are expected in 2008.

As network speeds continue to improve the environment

for innovative new data services will also prosper. If delivered

successfully, these new services will provide a lucrative new

revenue stream for operators. These new data services will

encompass many elements: location-based services, mobile

TV, social networking, mobile gaming and many more.

But the increase in bandwidth requirements for these new

services will mean that traditional backhaul networks based

on legacy technologies such as ATM will no longer remain a

cost-effective method for handling backhaul. Nor will they be

sophisticated enough to cope with functions such as qualityof service and resiliency management, which will be integral

parts of this new service delivery environment. For these

reasons, mobile backhaul is at risk of becoming the bottleneck

in todays mobile networks.

MPLS technology in the backhaul is the solution to this problem

for a series of reasons. The flexibility of the technology means it

will offer benefits and cost efficiencies in both legacy mobile

backhaul and for future environments based on new technolo-

gies such as LTE. This means existing technology investments

are protected and at the same time ensures that the technology

will remain sufficiently future proof and scalable.

The ability to support QoS, traffic engineering and resiliency

features will ensure that new services can be successfullyrolled-out, while mobile operators will be able to leverage

further cost benefits by using an MPLS-based backhaul

network to deliver many non-backhaul services.

The goal of the IP/MPLS Forum is to provide guidelines on

the architecture, scenarios and technology choices for IP/MPLS

RAN backhaul within the various network environments

(legacy, IP, converged).

The MMBI framework is based on the mobile network defini-

tions outlined by the industry standards organizations (3GPP,

3GPP2, WiMAX Forum etc.) The solution is based on MPLSspecifications and protocols developed at the IETF. The MMBI

initiative is also being coordinated with other mobile backhaul

activities underway at industry organizations such as the

Metro Ethernet Forum (MEF) and the DSL Forum.

For more information please visit:

http://www.ipmplsforum.org/ or e-mail [email protected]


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Fax: +1-510-492-4001

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i Pmp Ls Mobile Back Haul White Paper