Mplstp Based Mobile Backhaul Networks 572

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MPLS-TP based3G/LTE Mobile Backhaul Networks

Delivering new value through next-generation transport networks


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Contents

Introduction ..................................................................................................................... 3Mobile Network Evolution & Backhaul............................................................................. 4

TN700 Based Solution .................................................................................................... 7

LTE Mobile Backhaul ................................................................................................. 8

Multicast Support ..................................................................................................... 10

Network Clock Synchronization ............................................................................... 11

Interoperability with IP/MPLS Network..................................................................... 12

Enhanced OAM........................................................................................................ 12

End-to-end Service Provisioning.............................................................................. 13

Advantages over IP/MPLS Switch/Router ..................................................................... 14

Summary....................................................................................................................... 16


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Introduction

Over the last 10 years, the progress of mobile service has been one of the biggest industrysuccesses in history. 4 billion connections to mobile devices worldwide were achieved for thewireless industry in December 2008 as a historic milestone (Souring: 3G Americas). Thisestimate by Informa Telecoms & Media represents 60% of the entire global population today. Insome countries, millions of people are now experiencing connectivity to the world for the firsttime through wireless and changing their economic, social and political fortunes forever.

The number of wireless users on 3G services continues to rise. Informa estimates that there arenearly 415 million 3G subscriptions to date, with 77% share of the 3G market on UMTS/HSPAnetworks or 320 million connections, and the remaining 95 million on CDMA EV-DO. Thenumber of commercial UMTS/HSPA networks has risen to 258 in more than 100 countries,including 41 networks in 20 countries in the Latin America and Caribbean region.

As many emerging markets are achieving a new level of communication, wireless technologycontinues its rapid advancement into next generation mobile networks. Currently, more than 100operators worldwide, including most industry leaders, have announced expectations to migratenetworks to LTE from 2010 and beyond. LTE is the next evolution of mobile broadbandtechnology that utilizes OFDM-based technology and a flat-IP core network allowing anenhanced Internet experience on mobile devices.

However, these trends have created challenges for mobile operators, including fiercecompetition and margin pressure. In order to improve both their profit margins and more marketshare, mobile operators are rapidly developing new applications and services to attract andmaintain customers. Now increasing mobile users are going broadband applications, such asemail, text messaging, web access, and live video, benefitting from more and more portablehandset devices.

The mobile backhaul network is the critical link between the broadband subscribers and thenetwork. Mobile backhaul networks link the remote base stations and cell towards to the mobileoperators core networks and provide access to both the voice network and the internet. Mobileoperators increasingly are focused on mobile backhaul transport, largely because its costsrepresent up to 25 percent of their leased-line OPEX according to a March 2006 report byHeavy Reading, an independent analyst firm. One way to minimize transport costs whileincreasing network flexibility is migrate to a packet-based architecture, which achievesbandwidth savings through statistical aggregation of non-voice data services. A key concern ofthe migration to 3G network is that any steps towards supporting future demands must be not atthe expense of existing revenue generating voice services. One solution is to base the mobilebackhaul network on packet based technology, which inherently supports mobile data services

and can scale to meet demand, while at the same time support TDM and other legacy servicessuch as ATM via circuit emulation services and pseudo-wires.

Nevertheless, mobile operators are reluctant to base their mobile backhaul network onconnection-less packet networks. The concern is that connection-less networks will not becapable of providing the levels of quality and reliability necessary to support voice services.Connection-less packet networks also demand new operational procedures and re-training ofstaff.
http://www.3gamericas.org/documents/Global_3G_Status_Update1.pdfhttp://www.3gamericas.org/index.cfm?fuseaction=page&pageid=324%20http://www.3gamericas.org/index.cfm?fuseaction=page&pageid=324%20http://www.3gamericas.org/documents/Global_3G_Status_Update1.pdf


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Hence the dilemma facing mobile operators: the demands of future services are best met usinga packet based network, but connection-less packet networks could affect existing revenue-generating voice services. However with the introduction of connection-oriented packet

networks, there is a possibility of solving this dilemma.In this paper, we will present a migration plan using UTStarcom connection-oriented packettransport MPLS-TP solution, which provides a path to a fully packet based network with thelevels of quality and reliability that can support both existing and future services.

Mobile Network Evolution & Backhaul

The terrain of mobile backhaul network spreads from the first transport equipment connectingcell sites (e.g., BTSs/Node Bs/eNBs sites) to the transport aggregation equipment connectingcentral sites (e.g., BSCs/RNCs/aGWs sites). The mobile backhaul is considered to be

consisting of three segments, i.e., access network, aggregation network and metro/regionalnetwork (see Figure 2).

The mobile backhaul must be capable of transporting diverse mobile services including 2G, 3Gand future LTE services. The logical interfaces and the services transported through the mobilebackhaul are summarized in (not limited to) Table 1.

Standards Interfaces Underlying Transport

2G Abis between BTS and BSC TDM

ATM IMA over E1/T1, ATM over SDH3G Iub between NodeB andRNC

IP over Ethernet

S1 between eNB and aGWLTE

X2 between pair of eNB

IP over Ethernet

Table 1: Interfaces and Services

The 2G Abis interface between BTS and BSC can be based on TDM. The 3G Iub interfacebetween Node B and RNC can be based on ATM/IMA and IP over Ethernet. From a logicalperspective, the Abis and Iub interfaces are purely static point-to-point connections.

In the LTE network, the eNB has S1 and X2 interfaces. The S1 interface terminates on theaGW. The X2 interface runs between eNBs and is used for neighbor discovery, handovers andcell optimization. Each eNB needs to be able to communicate with its direct neighbors. Basedon LTE ongoing standardization and implementation, most likely, the S1 and X2 interfaces willbe based on IP over Ethernet.


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Figure 1: Mobile Backhaul Network Overview

Two types of fundamental connections must be established in the mobile backhaul. One is thepoint-to-point connection between the transport equipment connecting the cell sites and thetransport equipment connecting the central sites for transporting Abis, Iub and S1. The other isthe point-to-point connection between the transport equipments/interfaces connecting two eNBsfor transporting X2.

To enable the richness of potential applications, unicast and multicast should be supported bytransport equipments in mobile backhaul with efficient utilization of network bandwidth.

Also, IP/MPLS Forum has described the key requirements for mobile backhaul in the followingtable:

Mobile Operator Requirements Solutions / Test Areas

Support bandwidth growth and acompetitive cost model

Packet services in the radio access (RAN)networks

Support a diverse set of interfacetypes at cell site

MPLS ATM and TDM pseudowires, Ethernet,and IP

Implement network-based clocksynchronization

IEEE 1588v2, Real Time Protocol (RTP),Synchronous Ethernet, Network Time ProtocolVersion 3 (NTPv3), external clock reference

Resiliency on par with TDM network MPLS, PBB-TE, MPLS-TP/T-MPLS, and nativeEthernet resiliency mechanisms

Table 2: Mobile Backhaul Requirements

In addition, network clock and time synchronization plays a critical role when makingtechnology/vendor choice for mobile backhaul. It has particular relevance for LTE, because thistechnology requires not only highly accurate clock frequency synchronization, it needs time syncas well. The following table depicts the requirement for frequency and time sync for each of themajor mobile technology:


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Mobile Technology Clock Frequency Timing Phase

GSM 0.05ppm NA

WCDMA 0.05ppm NA

CDMA2000 0.05ppm 3sTD-SCDMA 0.05ppm 1.5s

WiMAX 0.05ppm 1 s

LTE 0.05ppm Time sync is required

Table 3: Network Clock and Time Sync Requirements


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TN700 Based Solution

UTStarcom TN700 series products represent the latest generation of equipment supportingCarrier Ethernet. Each product in this series is fully MEF9 and MEF14 certified and cantherefore be used for offering Carrier Ethernet Services. All of the TN700 products use high-speed backplane buses and high capacity packet switch fabrics which greatly enhanceefficiency and reduce the overall size and power requirements of the systems.

With its support for MPLS-TP, the TN700 products not only support Carrier Ethernet but thetransport of other legacy traffic including ATM, Frame Relay, and TDM providing carriers withthe option of offering those services as well. This allows an enterprise to migrate to CarrierEthernet as they gradually retire their legacy equipment.

Support for multi-protocol transport enables the TN700 to offer packet based mobile-backhaul

solution. As depicted in the diagram below, all different types of base stations e.g., 2G, 2.5G,3G, HSPA, or LTE can be connected to TN700 products and generated traffic can beaggregated over 10G POS (packet over SDH/SONET) or Ethernet links. The solution also iscapable of handling the inter eNodeB (X2 interface) communication for LTE in a very efficientand cost-effective manner using L2VPN mechanism. We will discuss this topic in more detaillater in this document.

BTSBTS

Node BNode B

eNB/Node B

Node BNode B

TN725

TN705

TDM n*E1 (copper)

ATM IMA n*E1/ T1 (copper)

STM-1 ATM (Fiber)

FE/GE (Fiber/ Copper)

10G/2.5G/155MPOS

10GE/GE

Cell SiteNetwork CO (Access)

SAToP (RFC 4553)

ATM over MPLS (RFC 4717)

CEP (RFC 4842)

EoMPLS (RFC 4448)

TN Solution Set

TN703E

Figure 2: Connecting Various Types of Base Stations to TN700

Using TN700 Solution, carriers can deploy next generation future-proof network that is based onsimple, easy-to-operate, and cost-efficient MPLS-TP technology. Use of this technology drivesdown the OPEX significantly, because it uses less power, less space, and makes use of existingpersonnel and their skill set. MPLS-TP supports deterministic-data plane (This means that theforward and return path for a LSP traverses through the same set of nodes) enabling it for


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predictable performance for all different traffic types. Furthermore, its enhanced OAMcapabilities make the trouble-shooting and fault localization much more predictable and reliable.With TN700 solution, a mobile operator can provide complete end-to-end backhaul solution

while maintaining the connectivity to existing IP/MPLS core and TDM/SDH/Microwave backhaulnetwork. TN700 solution also meets the stringent clock synchronization requirements for3G/4Gbackhaul. It supports Sync Ethernet and 1588v2. It also has very high clock accuracy of0.05ppm holdover over 24 hour time-period. Clock synchronization capability will eliminate theneed for local GPS or primary clock source reducing the OPEX further.

Cell Site Mobile Backhaul Mobile Core Network

2G BTS

3G Node B

3G Node B

3G NodeB orLTE eNodeB

BS C

aW G

RN C GGSNGGSN

MG WMG W

MSCMSC GMSCGMSC

SGSNSGSN

Operators Circuit Switching

Backbone Network

Operators Packet Sw itchingBackbone Network

SGSNSGSN

T1/E1 (Copper)

ATM(IMA/STM-1)

Ethernet(Fiber, GPON, xDSL)

A-bis

E1/T1

AAL2/5

ATM

E1/T1

IMA

AAL2/5

ATM

STM-1

IP

MLPPP

E1/T1

LTE

UDP/IP

Ethernet

STM

-1

ATM

STM-1chGbE/10G

bE

Any traffic overMPLS-TP

TN705

TN705

TN703

TN725

Unified Backhaul Networknified Backhaul Network

Figure 3: End-to-End Mobile Backhau l Solution using TN700

LTE Mobile Backhaul

TN700 provides full support for LTE mobile backhaul using L2 based VPLS and VPWS. L2Reference model can be found in [1]. As shown in the diagram below, the mobile backhaulnetwork can be created using TN703 for edge, TN705 for aggregation and TN725 fordistribution function. This network enables both S1 connectivity (eNodeB to aGW) and X2connectivity (eNodeB to eNodeB). To provide high availability, the aggregation switches can beconnected in a mesh topology. Combined with 0.05 ppm clock holdover accuracy, synchronousEthernet, 1588v2, and comprehensive OAM, the TN700 offers a highly reliable, future-proof,cost-effective and low maintenance backhaul solution.


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EPC (Evolved Packet Core)

P-GW P-GWS5 Connectivity

MME/S-GW MME/S-GWAge

o

Ac

Pool Area 1Pool Area 2

U-PE

N-PEN-PE

U-PEU-PE

U-PE

eN B

TN703

eN B

TN703

eN B

TN703

eN B

TN703

eN B

TN703

eN B

TN703 eN B

TN703

eN B

TN703

TN725 TN725

TN705 TN705

Figure 4: LTE Mobile Backhaul Solution

Connectivity between the base-stations is a unique function of LTE, it is known as X2 interface.X2 connectivity is achieved by implementing H-VPLS, where the edge nodes TN703 performsthe U-PE function and aggregation nodes TN705/TN725 perform N-PE function. A PW/LSP(VPWS) is setup from each eNodeB to other within a pool area via the aggregation node servingthe pool area, so that each eNodeB can reach its pool area neighbor directly as needed.Moreover the N-PE or aggregation nodes are connected via VPLS. If an eNodeB needs tocommunicate with another eNodeB under different aggregation node, the communication willoccur via the VPLS setup between the aggregation nodes. Please note that physical link forboth X2 and S1 connectivity will be the same between eNodeB and aggregation node.


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aGWeNodeBeNodeB

eNodeBeNodeB

eNodeBeNodeB

eNodeBeNodeB

U-PE

U-PE

U-PE

U-PE

N-PE

N-PE

U-PE

U-PE

VPLS

aGW

Inter-pool X2

Intra-pool X2

S1 Connectivity

Pool Area 1

Pool Area 2

VPWS

Figure 5: S1 and X2 Connectivi ty

As stated earlier, TN700 is based on MPLS-TP technology. By design, MPLS-TP doesntdepend upon IP layer (or addresses) for packet forwarding or OAM. The VPWS and VPLSservice setup doesnt require IP address information. This characteristic further simplifiesnetwork planning. It also important to note that according to recent study, in LTE, the traffic ofS1 I/F will occupy more than 95% of network traffic (X2 will be less than 5%). So S1 interfacewill contribute to majority of traffic. And in such scenario, transport technology such as MPLS-TP with static provisioning support is the best mobile backhaul solution for LTE.

Multicast Support

TN700 uses combination of H-VPLS and IGMP proxy/snooping to achieve the multicastfunction. In the following an example network is depicted. The TN700 form the H-VPLS network the distribution layer performs N-PE function and aggregation/access layer performs U-PEfunction

IPTV Feed

IP/MPLS

N-PE

U-PE

IGMP Proxy

eNodeBeNodeB

eNodeBeNodeB

eNodeBeNodeB

eNodeBeNodeB


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Figure 6: Mult icast Support

As Carrier-class Ethernet services are reaching wide spread deployment, a consensus is being

reached that transport networks need an evolution towards packet-based networking. However,with a confusing number of solutions in the marketplace deployment has been slow. Thesesolutions include NG-SDH with GFP/VCAT/LCAS, IP Routers with MPLS, T-MPLS and MPLS-TP.

Network Clock Synchronization

Highly accurate clock resiliency at par with TDM networks is one of the key requirements formobile backhaul application. Clock accuracy is critical for packet based services offered by 3G,HSPA, and LTE. TN700 has implemented several functions and mechanisms to ensure that allthe requirements related to network clock and time synchronization are met. The followingdiagram depicts the synchronization architecture for TN700 based network

1588v2 Eliminates theneed for GPS sync at eachcell-site1588v2 Eliminates theneed for GPS sync at eachcell-site

TDM BasedTiming

Distribution

~

PR CIEEE 1588

Grandmaster

SyncEthernet&1588v2

POSPOS

Ethernet

Node B

Node B

1

2

Scenarios:

RN C

TN703E Figure 7: Network Synchronization Architecture

With TN700 solution, the mobile operator has a choice of using traditional TDM clock, if Packetover SDH backhaul (using SSM/S1 byte) is deployed. For 10GE/GE backhaul, the clocksynchronization can be offered using Sync Ethernet (sync Ethernet is PHY point-to-point levelinterface for carrying network clock; resembles SDH/SONET clock distribution model).

For these applications, carrying time (time of the day) information accurately is equally critical.Sync Ethernet cant carry time of the day information. For carrying this information, TN700 hasimplemented a time over packet (ToP) protocol IEEE 1588v2. The ToP Server transmitstiming packets over asynchronous data path; the ToP slave recovers timing from these packets.ToP doesnt only requires end nodes to support 1588v2, the intermediate nodes are transparentto this protocol.


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Interoperability with IP/MPLS Network

As mentioned earlier in this paper, TN700 is based MPLS-TP. Since MPLS-TP data plane isbased on MPLS, the TN700 offer full compatibility with existing IP/MPLS core network. TN700may be deployed in each metro network and connectivity can be provided between thesenetworks via the IP/MPLS core. It is also possible to interconnect mobile-backhaul Metro tomobile core network via the same IP/MPLS core. The following diagram depicts some of theseIOP scenarios. TN700 has proven IOP with leading vendors products such Alcatel-Lucent,Cisco, and Juniper Networks.

Core Network(IP/MPLS)

Metro Network Mobile

(MPLS-TP)Metro Network

Enterprise(MPLS-TP)

Metro Network Enterprise

(MPLS-TP)

Mobile CoreNetwork

PERNC

TN703

TN703

TN703TN703

TN703

TN703

TN705TN705TN725

TN705TN705

TN703

TN725TN725

TN725

(A)

(A)

(B)

(B)

Internet

Figure 8: TN700 IOP with I P.MPLS based core

Enhanced OAM

One of the key strengths of MPLS-TP based TN700 is the standard based enhanced OAMsupport. The MPLS-TP working group continues to put significant effort on the integrated OAMfor MPLS-TP based networks. These networks will support both Ethernet OAM (ITU Y.1731,802.1ag, and 802.3ah) and MPLS/PW OAM (Y.1711). The working group has proposed a newframework for the OAM and has defined brand new functions such as Tandem Connection

Monitoring (TCM) getting direct inspiration from SDH/SONET space. Moreover the MPLS-TPmakes it mandatory to support OAM irrespective of operational condition of control plane(optional for MPLS-TP). The following diagram depicts the OAM framework for TN700 solution:


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B1

MPLS-TPMetro

MPLS-TPMetro B2

IP/MPLSCore

Access Link OAMIEEE 802.3ah


end to end LSP OAM ITU-T Y.1711

SegmentLSP OAM

SegmentLSP OAM

end to end ETH OAM IEEE 802.3ag/ITU-T Y.1731

MIP


MEP MEP

MEPMEP

MIP MIP

TN-A TN-B TN-Y TN-Z

P1 P2


MIP

MIP MIP

Figure 9: TN700 OAM Architecture

End-to-end Service Provisioning

UTStarcom TN700 solution comes with powerful e2e service provisioning NMS system Netman 6000. Netman 6000 supports all classical functions of a network management system

including topology management, device management, fault management, performancemonitoring, security management, and network provisioning. Netman 6000 implementsgeographical redundancy (carriers choice) to support business continuity and high availability.One of the key strengths of this NMS is service provisioning. The service provisioning layerhides the complexity of MPLS-TP and presents the network in a simplified manner to theoperator. In addition, it is possible to create LSP and PW (as part of VPWS/VPLS service) withbatch commands for efficiency, speed, and accuracy. Operator is also offered a built-in networkcapacity planner that empowers them to plan the network in a timely manner with much lesseffort.


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Primary OMC-O Server

DCN

OMC-O Clients

NM S

Proxy

NM S

Proxy

OMC-O Clients

TN705/TN725 TN705/TN725

Backup OMC-O ServerPrimary OMC-O Server

DCN

OMC-O Clients

NM S

Proxy

NM S

Proxy

OMC-O Clients

TN705/TN725 TN705/TN725

Backup OMC-O Server

Figure 10: Netman 6000 OMC-O Redundancy Architecture

Advantages over IP/MPLS Switch/Router

Connection Oriented and Deterministic Data Plane

Unlike IP/MPLS, the Label Switched Paths (LSP) and Pseudo Wire (PW) are established viaNMS using static provisioning. Such characteristic hide the complexity of underlying complexMPLS protocol. Also, since the path is setup statically, it is much easier to plan the network,because at any given time operator can view the overall network usage and based on thisinformation can expand the network in much more predictable and efficient manner. In addition,every LSP/PW connection is co-directional (also known as bi-directional), which means bothforward and return path will traverse through the same set of MPLS-TP nodes. This function isalso referred to as deterministic data plane. This function allows operators to not onlytroubleshoot the network with confidence; operators can identify the troublesome parts of thenetwork before the actual problem really happens.

Enhanced standards based OAM

MPLS-TP working group is putting tremendous effort in the OAM enhancement. Although isOAM is based on existing standards such as Y.7131 (Ethernet OAM), IEEE 802.1ag and802.3ah (Ethernet OAM), and Y.1711 (MPLS) OAM, the key differentiator is the frameworkitself. In MPLS-TP, more emphasis is on identifying each LSP/PW uniquely and then applyingvarious OAM functions to each MPLS-TP which participates in this path. The MPLS-TP OAMframe derives several concepts such as Tandem Connection Monitoring (TCM), which is usedfor inter-provider LSP OAM.


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Lower OPEX

MPLS-TP is based on L2VPN model of MPLS. The L3 implementation is in-general complex

and requires lot more processing power in IP/MPLS switch/router. As a result, IP/MPLSrouter/switch consumes lot more power than MPLS-TP. Additionally the MPLS-TP basedproducts can be made available in much smaller factor. Both power and real-estate savingsdrive the overall OPEX down. Also, since MPLS-TP is based on simple L2 architecture, thesesystems are much easy to operate compared to IP/MPLS router. In fact, any operations teamwho is currently handling SDH networks can easily trained on UTStarcoms MPLS-TP product,because we offer unique end-to-end service (LSP) provisioning via our NMS platform.


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Summary

Now mobile carriers are facing great challenges moving to an all-IP based network to get moreefficient bandwidth with a much lower cost per bit. Carriers must ensure to full utilize their oldnetwork for invest protection, and also want to make seamlessly and economically migration tothe new network.

The TN700 Solution provides operators with the flexibility to implement a smooth, cost-effectivemigration from 2G, 3G to future LTE in their mobile backhaul network. It combines the pros ofMPLS, pseudowire, and Ethernet technologies to provide not only legacy TDM and ATMservices with guaranteed SLAs, but also Ethernet service to ensure scalability for unpredictablebandwidth requirement and packet economics for a compelling business case. So TN700solution empowers mobile carriers to expand the scope of their network while reducing thenumber and complexity of network elements and the corresponding OPEX and CAPEX that

negatively impact profits. The TN700 solution also lets operators leverage UTStarcom industryleadership in the development of MPLS-TP network technology, as well as the carrier networkdesign, implementation and support experience.

References

[1] MPLS in Mobile Backhaul Networks Framework and Requirements IP/MPLS 20.0.0 Oct 2008

[2] MPLS Architectural Considerations for a Transport Profile April 2008

[3] MPLS-TP Framework draft-blb-mpls-tp-framework-01.rtf (www.ietf.org)
http://www.ietf.org/http://www.ietf.org/


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The information contained in this document represents the current view of UTStarcom on the issues discussed s of the date of publication. Please note the foregoing may not be acomprehensive treatment of the subject matter covered and is intended for informational purposes only. Because UTStarcom must respond to changing market conditions, theinformation herein should not be interpreted to be a commitment on the part of UTStarcom and the specifications are subject to change without notice. UTStarcom makes nowarranties, express or implied, on the information contained in this document

UTStarcom, Inc. USA1275 Harbor Bay ParkwayAlameda, CA 94502 USATel: 510-864-8800Fax: 510-864-8802

www.utstar.com

About UTStarcom, Inc.UTStarcom is a global leader in IP-based, end-to-end networking solutions and international service and support. Thecompany sells its broadband, wireless, and handset solutions to operators in both emerging and establishedtelecommunications markets around the world. UTStarcom enables its customers to rapidly deploy revenue-generatingaccess services using their existing infrastructure, while providing a migration path to cost-efficient, end-to-end IPnetworks. Founded in 1991 and headquartered in Alameda, California, the company has research and design operations

in the United States, China, Korea and India. UTStarcom is a FORTUNE 1000 company. For more information aboutUTStarcom, visit the companys Web site at www.utstar.com

Copyright 2009 UTStarcom, Inc. All Rights Reserved. UTStarcom, the UTStarcom logo, A World of BetterCommunication and mSwitch are registered trademarks of UTStarcom, Inc. and its subsidiaries. All other trademarks arethe property of their respective owners.

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Mplstp Based Mobile Backhaul Networks 572

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