Use of MPLS Technology in Mobile Backhaul Networks

WHITE PAPERUse of MPLS technology

in 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 substantialshare 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 Term Evolution (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, scalableand 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 .............. 1

Market Trends and Challenges ......... 2

Overview of IP/MPLS Forum’s MPLS Mobile Backhaul Initiative .... 3

Business Benefits of IP/MPLS Forum’sMobile BackhaulInitiative .................... 3

Architectural Overview................... 4

RAN EquipmentSynchronization........ 5

OAM and Resiliency................... 6

Conclusion................. 7

1IP/MPLS Forum White Paper

Third-generation mobile networks have become a reality. ByNovember 2007 there were 190 3G networks in commercialservice across 83 countries worldwide with over 800 differenttypes of 3G devices launched into the market available from around 90 suppliers (source: Global Mobile SuppliersAssociation. Dec 2007). There was forecast to be 252 million3G subscribers worldwide by December 2007 (source: InformaTelecoms & 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 fromlegacy voice services.

However, these new 3G-based services will also require a substantial increase in bandwidth, which will in turn lead togreater mobile backhaul costs. It is estimated that backhaulcan account for as much as 30% of a mobile operator’s 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 themigration to 3G. As well as extra traffic, backhaul will need to be able to handle a range of new functionality, includingQuality of Service (QoS) and resiliency management. Thesenew elements will become increasingly important as mobileoperators migrate towards packet-based backhaul networks.

Mobile operators will also be required to protect existing legacy technology investments for some years. At the sametime 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 thanjust mobile backhaul and it increasingly being used to carrytraffic for more than one mobile operator. This requires meth-ods of separating and securing multiple operator traffic whilemaintaining service level agreements. We estimate that asmany 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 valuefrom the network.

The new backhaul infrastructure must therefore meet threemain criteria: it must be flexible (to support both legacy and IPservices), scalable (to support emerging future technologies)and cost-effective (to compensate for rising levels of backhaultraffic). It also needs to be a converged network, which meansthe 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 interfaceenhancements (HSPA, EV-DO, Rev C, mobile WiMAX etc.) are rolled-out. However, global ARPU trends remain only flator negative, despite an uplift in the proportion of revenuesrelating to higher-bandwidth data services. This creates amajor business challenge with backhaul as a significant bottleneck (see figure 1).

A study by Infonetics Research suggested that the global market 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: “MobileBackhaul Equipment, Installed Base, and Services”, Infonetics Research, 2007)

2 Use of MPLS technology in mobile backhaul networks

Voice DominantTraffic

Revenues

Data Dominant

Time

Quan

tity

Cellular operatorrevenue & traffic

decoupled

Market Trends and Challenges

Figure 1: ARPU declines; bandwidth increases


Figure 2. Scope of MMBI

Overview of IP/MPLS Forum’s 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

Access Network

Access Network

Traffic Grooming at Cell Site

Traffic Grooming at Cell Site

The IP/MPLS Forum’s MPLS Mobile Backhaul Initiative (MMBI)proposes a framework for the use of MPLS technology to bringsolutions to transport RAN backhaul traffic over access, aggre-gation and core networks. The framework describes possibledeployment scenarios and provides recommendations on howto deploy MPLS in each of these scenarios. This will create areference guide that will allow vendors and operators to selectthe appropriate feature sets for their specific scenario.

The focus is on a shared network infrastructure that is able tosupport (emulate) existing legacy services (2G, 2.5G) as well asnew services based on 3G and beyond (Eg: HSPA, LTE). Thiswill 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 technologywherever 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), resiliencycapabilities, clocking and synchronisation, Operations andMaintenance (OAM), and support for various TransportNetwork Layers (TNLs), LTE and mobile WiMAX.

Business Benefits of IP/MPLS Forum’s Mobile Backhaul Initiative

This combination of rising traffic requirements coupled withdeclining revenues is a key motivation for operators migratingRANs to a converged, packed-based architecture (see figure1). MPLS has been globally deployed in these types of net-works and has been an important element by creating anenvironment for the delivery of new data services. As thesepacket-based networks grow in popularity, MPLS must nowalso be extended into to the backhaul.

This architecture will directly impact mobile operators’ bottomline by simplifying operations, reducing Opex and leveragingthe 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 protectinvestments 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 forproviding QoS, traffic engineering (TE), legacy layer 1 andlayer 2 emulation (via pseudowires) and resiliency features.These advantages can be leveraged for use in a wide varietyof network architectures and applications such as EnterpriseVPN, IPTV, mobile backhaul among others.


In the legacy environment, RAN equipment communicates viaeither TDM or ATM TNLs and are connected with a T1/E1interface, or with an Ethernet interface (Fast Ethernet) if TDMor ATM is encapsulated over Ethernet via IP or MPLS. Thefunctionality 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. TheHDLC 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 Forum’s MPLS Mobile Backhaul Initiative are defined for variousTransport Network Layers (TNL) and mobile network generations. These scenarios are grouped as follows and comprise twobasic categories: legacy (TDM, ATM, HDLC) and future (IP/Ethernet).

Network Specification TNL Speed (approximate)

GSM/GPRS (2G/2.5G) TDM 56 - 114 KbpsEDGE (2.5G) TDM 236.8 Kbps – 473.6 KbpsUMTS /HSDPA/HSUPA R3, R99/R4 ATM ~384 Kbps (uplink)(3G) R99/R5, R6 ATM ~ 2 to 3.1 Mbps (downlink)

IPCDMA 1x-RTT (2.5G) IS-2000 HDLC or TDM 144 KbpsCDMA 1x EV-DO (3G) IS-856 IP ~ 1.8 Mbps (uplink),

~ 3.1 Mbps (downlink)

Mobile WiMAX WiMAX Forum IP 50 MbpsNetwork 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 variousapplications allows it to be applied to legacy mobile backhaulnetworks as well as future technologies such as LTE. Forexample, the same MPLS network infrastructure can be usedto carry the legacy traffic pseudowires may also be used tocarry and provide QoS guarantees to next generation LTE traffic. Additionally, MPLS can be deployed on any layer 2technology capable of supporting MPLS labelled switching.

IP/MPLS - with its packet-switching advantages andpseudowire technology - is ideally suited to overcome the scalability limitations of traditional circuit based technologiessuch as ATM and TDM. MPLS permits support of these tech-nologies using pseudowires to protect existing investments inlegacy equipment. For future IP and Ethernet based interfaces,

it is possible to aggregate traffic over single TE tunnels andprovide differentiated services for this aggregate so that QoSrequirements are met while at the same time providing furtherimprovements 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 of other applications, the MPLS network also provides economiesof scale. This has a significant impact in reducing both a service provider’s capital and operational costs. Furthermore,investments in MPLS technologies benefit the service providerby making it “future proof” and still applicable in the fastevolving mobile technology scenarios (eg: LTE and beyond).

Mobile Core

Network(s)

3: BackhaulTransport Reliability

1: Radio Framing Accuracy

2: Hand Off Control

Node

Node RN

ET

ETBSCBSC


Future

RAN Equipment Synchronization

Figure 3: Clocking and synchronisation in RAN

In R5 3G, LTE and mobile WiMAX environments, the RANequipment interfaces use the IP TNL – either at the Iub inter-face (for 3G) or on R7/R8 for LTE or mobile WIMAX. Mobiletraffic over IP TNL can be transported either via Ethernetpseudowires or regular IP/MPLS TE tunnels over MMBI’smobile backhaul network. IP termination can take place eitherat the edge node, the access node, the access gateway ordirectly at the RAN equipment.

Various deployment scenarios arise depending on the location(and the extent) of MPLS technology in the mobile backhaulnetwork and whether it comprises both the access and aggre-gation sections of the network or just the aggregation section.

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 commonreference 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) tothe RAN equipment.

For example, in the case where the air-interface is based on TimeDivision Duplexing (TDD), the base station clocks must be syn-chronized to ensure no overlap of their transmissions within theTDD 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).


The MMBI outlines the following methods for clock distributionover an IP/MPLS based backhaul network. In the case of RANequipment with IP TNL (including LTE), packet based methodswhere the frequency reference is carried over packets (e.g.,based on Network Time Protocol (NTP)) may be used to deliverfrequency to address the frequency stability requirements of theradio equipment. For legacy TNLs, such as TDM, and ATM, adedicated 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 aswell 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 assynchronous Ethernet or IEEE 1588 v2 or by deriving timingfrom the PDH/SDH transmission mechanisms used in themobile 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 wideselection of flexible troubleshooting and OAM tools that enablethe deployment of a truly carrier-grade backhaul network.

These include fault detection methods to drive protectionswitching mechanisms such as MPLS Fast Reroute. Other protocols enable fault diagnosis, fault isolation (eg: LSP Pingand LSP traceroute) and performance monitoring. MPLS protocols also provide tools for loopback and connectivitycheck. Examples include VCCV for pseudowire-based MPLS

backhaul solutions and BFD for IP based MPLS backhaul solutions. These OAM tools will remain applicable for futureLTE 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 theIP/MPLS forum that support interworking between nativeLayer1/Layer2 OAM and MPLS OAM.

OAM and Resiliency


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 inpopularity. Mobile operators have also begun to develop strategies andtechnology roadmaps that will enable them to launch “4G” servicesusing 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 deliveredsuccessfully, these new services will provide a lucrative newrevenue stream for operators. These new data services willencompass many elements: location-based services, mobileTV, social networking, mobile gaming and many more.

But the increase in bandwidth requirements for these newservices will mean that traditional backhaul networks basedon legacy technologies such as ATM will no longer remain acost-effective method for handling backhaul. Nor will they besophisticated enough to cope with functions such as qualityof service and resiliency management, which will be integralparts of this new service delivery environment. For these reasons, mobile backhaul is at risk of becoming the bottleneckin today’s mobile networks.

MPLS technology in the backhaul is the solution to this problemfor a series of reasons. The flexibility of the technology means it

will offer benefits and cost efficiencies in both legacy mobilebackhaul and for future environments based on new technolo-gies such as LTE. This means existing technology investmentsare protected and at the same time ensures that the technologywill remain sufficiently “future proof” and scalable.

The ability to support QoS, traffic engineering and resiliencyfeatures 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/MPLSRAN 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 MMBIinitiative is also being coordinated with other mobile backhaulactivities underway at industry organizations such as theMetro Ethernet Forum (MEF) and the DSL Forum.

For more information please visit:http://www.ipmplsforum.org/ or e-mail [email protected]

48377 Fremont Blvd., Suite 117 Fremont, CA 94538Phone: +1-510-492-4056Fax: +1-510-492-4001E-mail: [email protected]

Documents

Use of MPLS Technology in Mobile Backhaul Networks