Nsn Epc White Paper

8/9/2019 Nsn Epc White Paper

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Enabling Mobile Broadbandgrowth

Evolved Packet Core

NSN White paperDecember 2013


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CONTENTS

Enabling mobile broadband growth 3

Enabling migration from current networks to LTE 4

The demand for cost-eective support of mobiledata growth

5

3GPP R8 Evolved Packet Core unies mobilenetworks

7

Solutions to match the needs of evolution steps 9

NSN is an end-to-end LTE/SAE vendor 17

Conclusion 18

Glossary of abbreviations 19


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Enabling mobile broadband growthIn recent times there has been a rapid growth in terminals, data cardusage and deployment of high speed networking technologies. Thesedevelopments have both, beneted from, and helped to drive up,the global accessibility of Internet. Today, wireless networks are seenas a viable alternative to xed broadband access leading to huge andcontinuing growth in mobile data business for operator.

The growth trend started with the launch of High Speed PacketAccess (HSPA) and the operators strategy to attract subscriberswith at monthly fee for using it. This business model has allowedmobile operators to compete with xed operators and oer mobilebroadband to consumer and business segments.

Mobile operators can support this growth cost-eectively by deployingmore ecient radio network technologies like Long Term Evolution(LTE) combined with ecient backhauling, simple network architectureand advanced tools in the Evolved Packet Core (EPC) to stay in controlof their network resources usage. The benet for subscribers is betterservice quality with increased bandwidth, lower latency and moreopportunities to use innovative services. And for operators, it all addsup to the ability to build more valuable customer relationships andenable new revenue opportunities in order to retain their business

cases.EPC forms part of Nokia Solutions and Networks’ (NSN) Liquid Net,a radically new architecture that unleashes frozen network capacityand creates a pool of resources that can move around the networkto full unpredictable demand, wherever and whenever people usebroadband.

Liquid Net encompasses Liquid Core, Liquid Radio and LiquidTransport. EPC is part of Liquid Core, which implements corevirtualization to enable any software application to run on COTSATCA® and ultimately on other generic multi-purpose hardware. Aswell as enabling the re-use of legacy hardware, core virtualization

enables operators to achieve greater hardware eciency and exibilityby dynamically allocating network resources to the various coreapplications in order to handle diering trac and service needs.


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Enabling migration from currentnetworks to LTE3GPP release 8 (R8) introduces major advances in mobile networks.For the subscriber, it means higher access rates and lower latencywhile for the operator, Long Term Evolution (LTE) radio technologyprovides lower cost per transmitted bit due to more ecient use ofradio network resources. The technology also oers more exibilityin frequency allocation due to its ability to operate LTE networksacross wide spectrum of frequencies. LTE also minimizes the powerconsumption of terminals that are used ‘always-on’.

3GPP R8 also introduces major advances in the core network thatimproves service quality and networking eciency leading to a betterend user experience. GPRS technology has already introduced thealways-on concept for subscriber connectivity and 3GPP R8 mandatesthis ability with at least one default bearer being always available forall subscribers. This allows fast access to services as well as network-initiated services such as terminating voice calls and push email. Theconnection setup time for person-to-person communication is alsominimized with always-on bearers.

Evolved Packet Core (EPC) was designed to support all mobile accesstechnology including LTE, 2G/EDGE, 3G/HSPA, evolved HSPA, CDMA,Wi-Fi and WiMAX and serves as a common anchor point for subscribersmoving between the dierent access networks. EPC’s ability tosupport both, LTE as well as current access technologies givesoperators a smooth migration path to LTE/SAE.

Besides providing connectivity between the radio network and thecontent and service networks, EPC also acts as the policy and chargingenforcement point. The mobile packet core gateway is the centralpoint through which all the trac travels making it the natural placeto enforce policy and charging rules.

TerminologyA 3GPP project, LTE, has specied Evolved UTRAN (eUTRAN) radiotechnology. eUTRAN is generally referred to as LTE radio.

In order to deploy LTE radio technology, operators need to upgradethe Packet Core. A 3GPP project, called Service Architecture Evolution(SAE), has specied Evolved Packet Core (EPC).

eUTRAN and EPC specications are included in 3GPP R8. The wholesystem including radio and core is referred to as Evolved PacketSystem (EPS).

EPS technology can be referred to as LTE/SAE.


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The demand for cost-eective supportof mobile data growthWith circuit-switched services, the amount of trac is directlyproportional to operator’s revenue. However, as developed marketshave reached saturation, operators have been forced into ercecompetition on voice call taris. The consequent fall in voice revenueshas been compensated for by improving network eciency with3GPP release 4 MSC Server System, which is already leading tocost-eective voice services.

Mobile networks are experiencing a transformation from circuit-

switched to packet-switched technology. Along with this development,the operator’s business model is changing from a pure serviceprovider to a service and connectivity provider. In circuit-switchedmobile networks, services are predominantly provided and controlledby the operator. Internet access is revolutionizing this business modelin packet-switched networks, where the operator provides connectivityand data transport. New methods are also needed to manage thegrowing volumes of data trac.

Driving down the cost per transmitted bitAn important business challenge that mobile operators are facingis the decoupling of the association between trac volume andrevenues. With revenue growth not keeping pace with the growth indata volumes, the only way for operators to retain protability is tolower the cost per transmitted bit.

Even though most capital and operational expenditures are due to theradio and transmission networks, there is also room for optimization inthe core network. Examples of improvements that can be introducedin today’s networks are deployment of all-IP interfaces with the radionetwork and adding Direct Tunnel in 3G networks. Mobile operators

Traffic volume

Revenue (€/bit)

Network cost ? (€/bit)

Time

Voice-dominated Data-dominated

Figure 1: The gap between mobile trac growthand revenue growth is expanding. The challenge isto shape the network OPEX curve according to therevenues, not the trac.


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are currently forced to maintain parallel networks for voice and data

services and considerable savings are expected when all services canbe oered over a single, IP-based network technology.

Enabling service evolutionLTE/SAE is designed to support all operator services, includingdata, high-quality voice and multimedia. Current packet-switchedmobile networks have been designed to accommodate user-initiated communications. If services and applications are to enablefacilities such as person-to-person communication, the network andterminals must support ‘always-on’ sessions, allowing subscribers to

be always reachable for incoming calls. Always-on sessions are alsoneeded for machine-to-machine applications (M2M).

For packet core, always-on sessions mean increasing demandfor higher subscriber density. Together with the 3GPP R8 atarchitecture, where all the mobility transactions are directly visibleto the core network, the signaling performance of the core networkelements must also be carefully considered.

Trac patterns in mobile networks are evolving. The originalassumption for mobile data services was that the operator providesthe services and access to corporate intranets. Currently, mobiledata subscriptions, particularly HSPA, are mostly used for both open

Internet access and company intranet access.

Staying in control of trac growthLTE radio technology will allow increasing amounts of trac to betransmitted over the network, increasing the operator’s need to stayin control of trac. Better technology is allowing the developmentof new applications and services, many of which the operator willneed to treat dierently to ensure users get the best possibleservice quality. Prioritized treatment is particularly important forpremium services such as operator VoIP and other high-quality

real-time services.

In current 2G/3G and CDMA broadband networks, there is alreadyan urgent need to deploy online usage control to service access.A typical example is the fair usage policies that are applied to setlimits to the maximum access speed that the subscriber is allowedto retrieve from the network or to limit the maximum amount ofdata consumed during the subscription period.


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3GPP R8 Evolved Packet Core uniesmobile networksEvolved Packet Core plays an essential role in unifying mobilenetworks, oering interoperability between LTE and existing wirelessaccess technologies. With these capabilities, it oers smoothtransition to 3GPP R8 architecture and technology, independent ofthe access technologies currently deployed in operator networks.

Evolved Packet System to carry all services

3GPP R8 species Evolved Packet System (EPS) as a at all-IP networkarchitecture that is ready to carry all operator services, from mobilebroadband data to high-quality voice and multimedia. EPC links thewireless access networks to the service and content networks. Inthis position, it is the natural point to enforce charging and tractreatment policies to allow the operator to stay in control of how theirnetwork resources are used.

Evolved Packet Core has to support LTE radio network, subscribermobility and oer interoperability between LTE and other operatoraccess networks. For this handovers between LTE and other networkshas to be supported and service continuity has to be ensured. 3GPP

R8 species optimized interworking between LTE and other 3GPPaccesses and CDMA to minimize handover times.

3GPP R8 architecture3GPP R8 architecture is simpler than current release 7 architecture(R7). The most important dierence is that the R8 network is an all-IPnetwork where all the services are provided over IP-based connections.However, interoperability with current circuit-switched networks is

Figure 2: 3GPP R8 architecture

Evolved Packet Core (EPC)

ePDG

SGSN

BSC

RNC

Radio Access NetworkOther access networks

eNodeB MME

S-GW P-GW

IMS

Services inPacket Data Network

Internet

Operator services

Company intranets

PCRFHLR/HSS AAA

HSGW

Charging

Control planeUser plane

Untrusted non-3GPP IP access

Trusted non-3GPP IP access

2G

3G

LTE

CDMA access network


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provided to ensure features like voice call continuity. Interoperability

with existing packet-switched networks is also specied, allowingsubscribers to move easily between dierent access networks.

Simplications are introduced by implementing the radio networkfunctionality in a single node, the evolved NodeB. Trac ows areseparated in the core network, that is user plane and control plane,allowing a more exible network architecture. The user plane data iscarried from the eNodeB directly to the S/P-GW. To handle control planetrac, EPC introduces a Mobility Management Entity (MME) that takesthe role of SGSN as a dedicated control plane element, taking care ofaspects like session and mobility management.

The Serving Gateway (S-GW) and Packet Data Network Gateway (P-GW)together takes the role of the current GGSN. These functions can beimplemented in one or two separate network elements. S-GW acts as a userplane anchor for mobility between the 2G/3G access system and LTE accesssystem. P-GW acts as mobility anchor for all accesses and as a gateway forInternet, company intranets, and operator services. It acts as a centralizedcontrol point for policy enforcement, packet ltering and charging.

3GPP R8 architecture is not only used for introducing LTE radio access;it is rather a new architecture for Packet Core. This basically means thatall new functionality dened by 3GPP will come to R8-based architectureand interfaces only. In the long run, all operators have to move to R8architecture in order to benet from new functionality. 3GPP R8 upgradewithout EPC is the right approach for operators who are currently delayingthe introduction and deployment of LTE.

For example, an operator can deploy R8 for 2G/3G networks only. And asMME is purely for LTE access, he does not need it from the beginning. Thisscenario can be deployed by rst upgrading GGSN to P-GW connecting toR7 SGSN via Gn, or by upgrading SGSN to R8 and connecting to S/P-GWwith S4 interface; and then adding MME later when LTE radio access isbeing taken into use.

Basically, EPC is not only intended for LTE access, but is actually anevolutionary step towards a common core for 2G, 3G, and LTE radio access.

Operators can still have SGSN and GGSN network elements for 2G and3G access in an R8 architecture. While SGSN is a must for 2G and 3G,GGSN is also possible, because 3GPP has agreed GGSN in R8 and laterarchitectures. There is no dierence between GGSN and P-GW withGn from 2G/3G perspective, since 3GPP species that P-GW with Gninterface also supports stand-alone GGSN functionality, and all new 3GPPfunctionalities should work in both logical elements. For instance, 3GPPhas agreed that R8 GGSN provides the same charging as P-GW (CDR). Themain dierence between these logical network elements is that P-GWadditionally provides S5 interface and related functionalities for LTE andEPS bearers.

From operator point of view, moving from R8 packet core to LTE/EPCis simpler than from R7 packet core. This is due to fact that the radionetwork needs anyhow changes when moving to LTE.


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Solutions to match the needs ofevolution stepsOperator networks need to be upgraded to LTE/SAE in smooth stepsthat ensure service continuity for subscribers. This evolution towardsEvolved Packet Core can be started today.

Introducing EPC in the operator networkIntroducing EPC in a operator network can be performed in steps whiletaking advantage of the synergies with 3GPP R7 architecture.

Leveraging the synergies with 3GPP R7

3GPP R8 is a logical evolution from earlier 3GPP releases and allowsexisting 3GPP operators to take advantage of the synergies with theirexisting networks. For HSPA operators, 3GPP R7 already speciesseparation of user plane and control plane trac handling. DeployingDirect Tunnel to carry the user plane trac directly from the radionetwork to the GGSN, operators can save up to 30 % OPEX costs,mainly due to transmission network savings. With R7 Direct Tunnel, thenetwork architecture is already aligned with 3GPP R8 architecture thatmandates user plane and control plane separation for LTE networks.

User Plane and Control Plane separation considerably simpliesnetwork design decisions, making it easier for the operator to adaptto growth in both subscribers and trac. LTE networks are introducedfor mobile broadband and early adopters of the services are expectedbeing high volume subscribers. An exception occurs in 2G networkswhere Control Plane and User Plane trac ows are tightly coupled.This sets some limitations in alignment of 2G and LTE networkarchitectures, as the 2G SGSN has to also handle the user plane trac(besides control plane). Operators introducing 3GPP R8 and LTE alsobenet from the all-IP networking synergies. Upgrading interfacesto IP, especially deploying Gb and Iu interfaces over IP, allows the

transport network technology to be unied and prepared for theall-IP 3GPP R8. The existing SGSN pooling concept, multipoint Gb/Iu,

3GPP R7: Direct Tunnel 3GPP R8: Flat architecture

GGSNRNC

SGSN

MME

P-GWS-GW

eNodeBsNodeBs

User planeControl plane

Figure 3: Direct Tunnel and 3GPPR8 at architecture


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currently deployed in 2G/3G networks, is also specied in 3GPP R8 for

LTE via MME pooling over the S1 interface.In current 2G/3G networks, the common factors of 2G and 3Gtechnologies are used in both control and gateway deployments. As 2Gtrac volumes are modest compared to HSPA and LTE trac volumes,decisions on network optimization should always be driven by thesebandwidth intensive technologies. In other words, the synergy benetsof 3G and LTE technologies outweigh the benets of combinedcontrol for 2G and 3G. 2G, 3G and LTE consume equal amounts ofcontrol capacity per supported bearer, but HSPA and LTE can carryconsiderably larger trac volumes (user plane). Because of this,network expansions will concentrate on 3G/HSPA and LTE technologies.

EPC as overlay versus upgrade deployment

The main advantage of introducing 3GPP R8 EPC is the possibilityto introduce LTE radio technology. EPC is, however, specied to bebackwards compatible and can also be applied to serve existing 2G/3Gnetworks. It also supports interoperability with non-3GPP technologieslike CDMA and WLAN.

The two key alternatives for EPC deployment are introduce the MMEand S/P-GW functionalities as software upgrades to the existingpacket core platforms or deploy the functionalities on stand-aloneplatforms in an overlay type setup. As 3GPP R8 introduces majorchanges and improvements to the packet core network, it is benecial,at least in the early phases of technology introduction, to apply EPCin isolation from the existing packet core to keep the main productionsystem intact. The introduction of EPC is also a logical period tointroduce next generation packet core nodes to meet the increasedrequirements in trac volumes, signaling and subscription handling.

LTE sets new requirements on the packet core. On the control side,these include adapting to the at architecture where MME acts as a

eNodeBs

MME pool MME pool

Gateway

Serving PDN

S5

Gateway

Serving PDN

S5

“Flex”S1-MME

S1-U

Control plane

User plane

Trackingarea 3

Trackingarea 2

Trackingarea 1

Figure 4: S1 Flex interface forMME pooling with geographicalredundancy


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dedicated control element. It also includes the ability to support the

increase in mobility management transactions when the operator’sprimary voice service migrates from a circuit-switched network to LTE.

On the gateway side, LTE and mobile broadband in general demandssupport for increasing trac volumes.

With at architecture, the gateway also plays a part in subscribermobility transactions, while introducing more options in networktopology. Another factor is that dierent services set dierentrequirements on the network topology. Despite the majority of servicesbeing provided from the Internet, operators still need to stay in controlof the usage of their network resources. The importance of both staticand dynamic policy control is increasing in line with the rising usage ofreal-time services. Subscription types can be dierentiated by enforcingpolicies governing bandwidth usage and charging.

Stepwise migration to 3GPP R8 EPCThe key functions of the Packet Core network are to support subscribermobility, provide connectivity between the radio access network andthe service networks and serve as a centralized control point to enforceoperator business policies. 3GPP R8 allows operators to migratefrom their existing Packet Core to EPC in smooth steps, ensuring thesubscribers see no major disruptions as their network evolves.

EPC introduction with minimum changes to the existingpre-R8 Packet Core

Deploying EPC as an overlay allows LTE to be introduced withminimum changes to the existing pre-R8 Packet Core. According to3GPP R8, the P-GW supports in-built GGSN functionality includingGn interface support. The Gn interface can also be applied between2G/3G SGSN and a stand-alone MME element to support handoversbetween 2G/3G networks and LTE. In handovers between the accesstechnologies, EPS bearers are mapped one to one to 2G/3G PDPcontexts and vice versa.

BSC

RNC

eNodeB

2G

3G

LTE

Pre-R8

SGSN GGSN

S-GW

S5

Gi

Gn

(Gn) (Gn)

P-GW

MME

SGi

Operatorservices

Internet

Corporate

services

Figure 5: EPC deployed as overlayon top of existing 2G/3G network


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As P-GW is the anchoring point for LTE subscribers, independently ofwhich access network they use, connectivity must also be providedbetween 2G and 3G access networks and P-GW.

Upgrading Packet Core to R8 level

3GPP introduces new interfaces between the network elements.Known as S interfaces, they form the basis of new feature developmentand improvements in 3GPP from R8 onwards. An example of the

improvements is deploying GPRS Tunneling Protocol version 2 (GTPv2)in control plane signaling. In order to keep the 2G/3G packet corenetwork aligned with the development, the G-interfaces must beupgraded to S-interfaces. For the 2G/3G SGSN, this means softwareupgrades to support the S3 interface with the MME and the S4interface with S-GW.

GTPv2 provides EPS bearer and QoS model where P-GW sees all LTE/3G/2G access similarly, which proves benecial from policy controland charging standpoint. GTPv2 also has advantage from mobilityperspective as it can move all bearers of the users in single mobilitytransactions.

BSC

RNC

eNodeB

R8

SGSN GGSN

S5

Gi

Gn

S4S3

P-GW

MME

S12

S-GW

SGi

2G

3G

LTE

Operatorservices

Internet

Corporateservices

Figure 6: Upgrading existing2G/3G network with 3GPP R8

interfaces

Figure 7: Common gateway for all3GPP accesses

BSC

RNC

eNodeB

R8

SGSN

S5

SGi

S4

S3

P-GW

MME

S12

S-GW

Operatorservices

Internet

Corporateservices

2G

3G

LTE


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Using the S3 interface makes intersystem mobility between LTE

and 2G/3G networks more exible. This allows bearer managementaccording to 3GPP R8, including Dual Stack Bearer (IPv4/IPv6) supportand QoS in the core. The full set of R8 features, including local mobilityanchoring for roaming users, minimizes the signaling load for thehome network.

Towards a fully integrated R8 network

In the integrated scenario, all accesses including 2G/3G accesses use acommon gateway, the 3GPP R8 S/P-GW.

With Direct Tunnel and S4 interface, the 3G SGSN is very tightlyaligned with Evolved Packet Core architecture and can provide

synergies when deployed in the same physical network element as theMME. According to 3GPP specications, the handling of user plane andcontrol plane trac is tightly coupled in 2G SGSN and Direct Tunneltype optimization is not possible. This limits the synergy benetsthat can be attained by deploying 2G SGSN in the same physical nodeas the MME. Many operators may nd it best to continue using theirexisting SGSN for 2G trac handling.

The common gateway for 2G, 3G and LTE provides obvious synergies,yet the operator may decide to upgrade existing GGSN to allow serviceaccess to LTE subscribers. In this scenario, low bandwidth servicessuch as WAP browsing and MMS would remain in the existing GGSN,whereas high volume services such as Internet and corporate intranetaccess would be migrated to the S-GW/P-GW that also allows serviceaccess for 2G/3G subscribers.

Upgrading the GGSN to a 3GPP R8 P-GW early will make the futureupgrade to LTE much simpler. Also, using a R8 SGSN will simplify takinga combined SGSN/MME into use when LTE is introduced.

Upgrading the Packet Core network elements to R8 lets operatorsbenet from additional features like new PCRF cases and the simpliedroaming model of R8.

There are various PCRF cases with Gx interfaces in use, which havedierent implementations for PDP context and EPS bearer handling.Therefore operators would rather not choose the “old” way to startwith policy deployments knowing that they would need to makechanges in any case. With GTP-based S8 interface for roaming(between S-GW and P-GW), operators benets as all roaming will takeplace between these two network elements only and Direct Tunnel canbe used in roaming cases and later when LTE is used.

Uninterrupted services supportLTE/EPC is designed to support all services, including the operator’s

primary voice service. In order to achieve this, EPC bearers are always-on, allowing fast call setup and ensuring subscribers are alwaysavailable for incoming calls. LTE radio interface provides more ecientradio usage for VoIP via maximized terminal battery lifetime and


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minimized latency. The at architecture contributes to the optimized

path for user plane trac and minimal latency.

Ensuring continuity for voice service

Today, a operator’s primary voice service is provided over the circuit-switched network. Primary in this context refers to the voice servicethat the user gets when picking up a mobile phone and dialing anumber. The operator may oer a secondary voice service comparableto Internet-based VoIP service.

In an early phase of LTE deployment, the most commonly availableterminals will probably be data cards for laptops. For this kind ofterminal, the secondary voice service is oered with VoIP clients. When

handheld LTE terminals become available, subscribers will expectthe primary voice service to be available. The short to mid-termsolution to enable operators to provide primary voice service to LTEsubscribers is Circuit Switched Fall Back (CSFB), which is specied in3GPP R8.

In the CSFB scenario, the end user terminal is simultaneously attachedto both the EPS (MME) and CS (MSC) domain. When the user initiatesor receives a voice call, the UE is moved from LTE to the 2G/3G CSnetwork before the call is set up. The procedure is standardized in3GPP R8.

Later, as LTE radio coverage increases, it becomes possible to consideroering the operator primary voice service over the LTE network. LTE/SAE networks can support high-quality voice, through:

• Always-on connectivity allowing short connection setup times

• Minimum latency on the transmission path and

• Quality of Service (QoS) management for both the voice media andassociated Session Initiation Protocol (SIP) signaling.

When subscribers leave the LTE radio network coverage area, the activevoice sessions must be handed over to another access network. If theoperator is already providing VoIP over HSPA service, the sessions can

be handed over to the HSPA network.For cases where the voice session is handed over from LTE VoIP toCS voice, 3GPP R8 species the so called Single Radio Voice CallContinuity (SRVCC) scenario. SRVCC is one directional, only allowingswitching the current voice call from LTE to 2G/3G CS radio. Theprocedure of handing over a voice session to 2G/3G CS voice isstandardized in 3GPP R8.

Simultaneous voice and data sessions can be supported duringhandovers in a 3G network when the multi-Radio Access Bearer (RAB)is enabled, and in a 2G network when Dual Transfer Mode is enabledin both CSFB and SRVCC scenarios.

The ultimate aim is an all-IP network where IP Multimedia Subsystem(IMS) is the 3GPP standardized connectivity control machinery forvoice and multimedia sessions.


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Supporting messaging and WAP

WAP and Multimedia Messaging Service (MMS) are pure data servicesand can be supported today in LTE networks. For SMS there are twooptions:

• CS fallback solution where the SMSs are sent and received betweenUE and MSC over an EPS network so that MME tunnels SMS over LTEand uses an SG interface with the MSC.

• Generic SMS over IP solution where IMS provides SMS support andEPS provides a bearer for SMS transfer.

Policy enforcement to manage the growthEvolved Packet Core has an essential role of enforcing policies to keepthe operator in control of network resources. Policies are applied toenforce dierentiation between subscribers and services. An example ofa subscription-based dierentiation is controlling the maximum accessspeed that the subscriber is able to retrieve from the network. Whenhigh-quality real-time services, in particular, operator primary voicehas to be oered, policies must be applied to guarantee the necessarybandwidth and minimum transmission delay for these data ows.

Operator tools to enforce policies include allowing, limiting or denyingtrac ows according to the selected policy and applying charging

control. The Quality of Service (QoS) level can also be dierentiatedbased on the service or application accessed.

Policy control architecture

According to 3GPP R8, the Policy and Charging Rules Function (PCRF)acts as a centralized point to control policy and charging. PCRFprovides the rules for the Policy and Charging Enforcement Function(PCEF), which resides in the mobile gateway.

The benets of deploying centralized policy enforcement in mobilenetworks are widely recognized as this strategy minimizes the numberof network elements and thus the OPEX costs. Trac detection

functionality is implemented in the gateway element together withall policy enforcement capabilities in order to simplify networkarchitecture and management.

Charging

Charging is an essential tool in enforcing operator’s business models.While migrating the network from 2G/3G to LTE, it is essential thatcontinuity of the existing business models is supported for bothpacket-switched and circuit-switched services. In practice, this meanssupporting similar charging models independently of the deployedradio access technology.

Online charging control is generally deployed for both prepaid andpostpaid subscriptions, and the need to support this remains validin EPC as well. By deploying online charging control for prepaid


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MME dimensioning S/P-GW dimensioning

Sessiondensity

Signalingcapacity

IndependentDPI

Throughputcapacity

Featureintelligence

Signalingcapacity

Flatarchitecture

Subscriber &Sessions density

MME dimensioning S/P-GW dimensioning

Subscriber &Sessions density

Throughputcapacity

Sessiondensity

Flatarchitecture

Signalingcapacity

Signalingcapacity

IndependentDPI

Featureintelligence

subscribers, the operator can minimize fraud in service usage. Use

cases for online charging control for postpaid users include companiesthat want to set limits on their employee’s use of data services.

Flow-based charging is generally applied in current 2G/3G networksand will also have application in LTE networks. Examples of there areapplication of time-based charging for VoIP calls and dierentiatedcharging of services provided by the operator.

Enforcing fair usage policies

Fair use policies allow the operator to control the usage of networkresources, ensuring fair sharing of available capacity among thesubscribers. Fair use policies can be implemented in various ways such

as setting limits as per access speeds and the data download duringthe subscription period. With automated interactive user dialogs, theoperator can encourage usage and sell more subscription packages tothe subscriber.

Dimensioning an Evolved Packet Core networkEvolved Packet Core dimensioning is fundamentally dierent fromdimensioning a traditional 2G/3G GPRS network. 3GPP R8 mandatesa at architecture that causes a number of changes in the process ofnetwork dimensioning. MME dimensioning is simplied, as it is a pure

control element dimensioned according to subscribers and transactionswithout being aected by user plane trac. With 3GPP R7 DirectTunnel, the same simplication can be achieved in current 3G networks.

As eNodeBs are directly connected to the gateway in the user plane,all the mobility transaction events are directly visible to the gateway.The number of transactions will dramatically increase with theintroduction of LTE where all the attached subscribers always haveat least one active EPS bearer. With dedicated control and gatewayelements, operators can adapt to the changes in usage patterns andtrac load in the network.

Figure 8: Scalability of MME andS/P-GW


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The following key dimensioning parameters for mobile Packet Core

must be supported simultaneously and have to scale independentlyof each other:

• Throughput capacity to support non-real-time services and packetsper second to support real-time services

• Number of subscribers to allow high subscriber density

• Number of transactions per second to support subscriber mobility

• Feature intelligence to optimize signaling and mobility handling inat architecture

• Service intelligence (DPI) to ensure user experience while optimizingnetwork resources

NSN is an end-to-end LTE/SAE vendorNSN LTE/SAE oering covers the whole end-to-end system includingeUTRAN radio network, Evolved Packet Core, transport and backbonesolutions, charging and subscription data management solutions aswell as network management and services to design, build and operatethe networks.

For Evolved Packet Core networks, we oer the MME and S-GW/ P-GW functionalities based on next generation Advanced TCA (ATCA)

platforms. We see the introduction of Evolved Packet Core as a timelydevelopment to upgrade the Packet Core elements to meet futureneeds. Those operators currently deploying 3GPP R7-based SGSN orGGSN functionality in their networks can smoothly evolve by upgradingthe ATCA-based elements to 3GPP R8 with software. NSN’s FlexiNetwork Gateway (Flexi NG) supports combined operation modesof S/P-GW and GGSN to ease network migration and the combinedMME/SGSN functionality will be supported by our Flexi Network Server(Flexi NS).

Evolved Packet Core mandates MME as a dedicated control planeelement. As the leading vendor for 3GPP R7 Direct Tunnel with

3GPP standardization, we were the rst to implement it. With thelargest number of implementations in live operator networks, wehave gained a solid understanding and experience in at architecturenetworks, which is reected in our EPC oering.

Rapidly increasing data volumes in mobile networks, the pressure toreduce the cost per transmitted bit and the prospect of eventuallyoering all services including voice over LTE/SAE networks areencouraging operators to use the greater eciency of LTE. This keytransformational shift requires a solution that ensures a high-qualityend-user experience at an optimal cost.

NSN, with the largest customer base worldwide, deep insights inpacket core technology implementation and a driving role in 3GPPstandardization has a comprehensive end-to-end view of LTE and EPC.


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ConclusionEvolution of terminals and networking technology coupled withInternet access as a global phenomenon are allowing advancedoperators to report dramatic growth in mobile data usage. None ofthese three alone could have set o the boom in data services usagebut the combination of all three have been fundamental to its growth.

3GPP R8 and LTE/SAE form a unifying evolutionary step for all existingmobile networks including 3GPP and 3GPP2 networks, as well asWi-Fi and WiMAX. EPC has an essential role in supporting the LTEradio network and in maximizing the return on investment made inthe network. It is the link between Internet, intranets, and operatorservices and the LTE radio access, supporting subscriber mobility withservice continuity across dierent network technologies. Serving as acentralized aggregation point for the trac ows, the EPC is a naturalpolicy enforcement point that allows the operator to stay in control ofnetwork resource usage.

The key components of EPC are MME and S/P-GW. 3GPP R8architecture allows the MME to be dedicated to handling controlfunctions, essentially for supporting subscriber mobility transactionsin the network. The gateway must be designed to take into accountthe increased data volume and packet processing requirements, high

subscriber density and the need to support mobility transactions inthe at architecture.

Introducing EPC in operator networks is best performed in steps. Bydeploying a Direct Tunnel solution, operators can start migrating theirnetworks towards 3GPP R8 architecture today. In the initial phaseof EPC deployment, the MME and S/P-GW functionalities are bestimplemented with an overlay solution, leaving the existing productionnetwork intact. Interoperability with the existing 2G/3G network canbe introduced without any upgrades to the existing system. In thefollowing phases, the 2G/3G network elements can be upgraded to3GPP R8 level. The ultimate target is a 3GPP R8 common core network

where all accesses are served by a common gateway.More than 20 operators have implemented NSN’s Liquid Net usingEPC for 4G LTE. This switch to a more uid and dynamic network issimplied because Liquid Net is based on evolutionary change ratherthan wholesale revolution, allowing operators to start transforming anetwork in any domain at any time.


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Glossary of abbreviations2G 2nd Generation of Mobile Telephone

Systems (GSM)

3G 3rd Generation of Mobile TelephoneSystems (UMTS)

3GPP 3rd Generation Partnership Project

3GPP2 3rd Generation Partnership Project 2

AAA Authentication, Authorization, andAccounting

ATCA Advanced Telecommunications

Computing ArchitectureBSC Base Station Controller

CDMA Code Division Multiple Access

CDR Charging Data Record

CS Circuit Switch

CSFB Circuit Switched Fallback

DPI Deep Packet Inspection

EDGE Enhanced Data rate for GSM Evolution

eNodeB LTE Base Station

EPC Evolved Packet CoreEPS Evolved Packet System

eUTRAN Evolved UTRAN

Gi Interface to PDN, e.g. Internet

GGSN Gateway GPRS Support Node

Gn Interface between SGSN and GGSN

GPRS General Packet Radio Service

GTP GPRS Tunneling Protocol

Gx Interface between P-GW and PCRF

HDTV High Denition Television

HLR Home Location Register

HSPA High Speed Packet Access

HSS Home Subscriber Server

IMS IP Multimedia Subsystem

IP Internet Protocol

LTE Long Term Evolution

M2M Machine-to-machine

MME Mobility Management Entity

MMS Multimedia Message System/Service

MSC Mobile Switching Center

NodeB 3G Base Station

OPEX Operational Expenditure

PCEF Policy and Charging EnforcementFunction

PCRF Policy and Charging Rules Function

P-GW Packet Data Network Gateway

PDN Packet Data Network

PDP Packet Data Protocol

QoS Quality of Service

R8 Release R8 (3GPP)

RAB Radio Access Bearer

RNC Radio Network Controller

SAE Service Architecture Evolution

SGSN Serving GPRS Support Node

S-GW Serving Gateway

S/P-GW Serving GW / PDN GW

SIP Session Initiation Protocol

SMS Short Message System/Service

SRVCC Single Radio Voice Call Continuity

UE User Equipment

UMTS Universal Mobile TelecommunicationSystem (WCDMA)

UTRAN UMTS Terrestrial Radio Access Network

VoIP Voice of IPWAP Wireless Application Protocol

Wi-Fi Wireless Fidelity (IEEE 802.11b wirelessnetworking)

WiMAX Worldwide Interoperability for MicrowaveAccess (IEEE 802.16)

WLAN Wireless Local Area Network (IEEE 802.11)


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