Ericsson Review No. 2, 1999 89

The Mobility Gateway provides what is re-ferred to as interworking location register(ILR) functionality. This functionality isneeded because different networks use dif-ferent protocols to communicate betweennodes, such as the home location register(HLR) and the mobile switching center(MSC). Specifically, GSM networks use themobile application part (MAP) protocol,whereas TDMA/AMPS networks use theAmerican National Standards InstituteANSI-41 protocol (Figure 1).

To ensure a truly open environment thatsupports multi-vendor connectivity, mes-sages implemented in the Mobility Gateway

Jambala Mobility Gateway—Convergence andinter-system roamingAndré Bertrand

As business becomes truly global and international, the need to communi-cate anytime, anywhere becomes more crucial. The demand for interna-tional roaming has grown spectacularly and is expected to continue grow-ing into the new millennium.

With the tremendous installed base of GSM and TDMA/AMPS wirelessnetworks in the world, international roaming has evolved to require inter-system roaming capability; that is, roaming between GSM andTDMA/AMPS networks. In addition, operators seeking to enter estab-lished wireless markets are increasingly requiring the use of inter-systemroaming to enable them to use the cellular coverage offered by partners inthe same or neighboring areas.

The author describes the Jambala Mobility Gateway, a new applicationfrom Ericsson that provides the level of convergence necessary to inter-face GSM and TDMA/AMPS networks.

conform to TDMA/AMPS (IS-41, revisionsB and C, and ANSI-41, revision D) and GSMstandards (MAP versions 1 and 2). Further-more, the Mobility Gateway does not im-pose any modifications on individual net-work components, such as HLRs andMSC/VLRs in current GSM andTDMA/AMPS environments.

The mapping of MAP and ANSI-41 pro-tocols allows for the exchange of informa-tion needed to provide basic mobility man-agement across different networks, thus per-mitting users to roam from one network toanother. Consequently, the protocols andinterfaces associated with service delivery in

TDMA / AMPS network

Dual-standard handset

ANSI-41

Mobility Gateway

MAP

GSM network

Figure 1 Inter-system roaming.

Jambala™ is a trademark owned by Telefonaktiebolaget LM Ericsson, Sweden.

Java™ is a trademark owned by SunMicrosystems, Inc., USA and other countries.

TRADEMARKS

90 Ericsson Review No. 2, 1999

different networks begin to look increas-ingly similar, even though the physical net-work elements are different.

The presence of a GSM subscriber in aTDMA/AMPS network is indicated by theMobility Gateway receiving a registration no-tification invoke message from the servingMSC (Figure 2). For the roaming subscriber,the Mobility Gateway is perceived as aTDMA HLR (with respect to the servingTDMA MSC), translating the registrationnotification message into a correspondingGSM update location message and sending itto the subscriber’s GSM HLR. As viewedfrom the GSM HLR, the Mobility Gatewayfunctions as a GSM VLR. Information re-ceived in insert subscriber data messages issaved in the subscriber’s profile in the Mo-bility Gateway and mapped onto the ap-propriate data used in the registration notifi-cation return result message. After the updatelocation result is received in the MobilityGateway, it generates the registration notifi-cation return result and sends it to the servingMSC.

It is important to note that the MobilityGateway does not replace existing HLRs inGSM and TDMA/AMPS networks. For asubscriber roaming between these net-

works, there will always be only one sub-scription, either in a GSM HLR or in aTDMA HLR, but not in both. The Mobil-ity Gateway contains the information nec-essary to identify the subscriber when eithernetwork is being used. If the subscriber isroaming in the other network type, the Mobility Gateway accesses the HLR in thesubscriber’s home network and forwards theinformation to the other network usingANSI-41 and GSM MAP messages as appropriate.

Reduced signaling loadTo reduce the signaling load, the MobilityGateway stores subscriber profiles based onreceived and derived information whilemapping and transferring information be-tween GSM and TDMA/AMPS networks.The subscriber profile is then available inthe Mobility Gateway and can be sent toserving VLRs without accessing the HLReach time. When the profile of a TDMA sub-scriber changes in the subscriber’s HLRwhile the subscriber is roaming in a GSMnetwork, the serving GSM VLR is notified(and the Mobility Gateway transparentlyupdates its record). Figure 3 illustrates the

TDMA or dual-standard handset GSM subscription

Mobility Gateway

6

345

2

7

1 8

HLR MSC/ VLR

GSM network

TDMA / AMPS network

“VLR” “HLR”

Figure 2Registration/location update of a GSMsubscriber roaming in a TDMA/AMPS net-work.Key:1 = Registration access2 = Registration notification invoke3 = Update location invoke4 = Insert subscriber data invoke5 = Insert subscriber data result6 = Update location result7 = Registration notification return result8 = Registration accepted message

Ericsson Review No. 2, 1999 91

scenario in which a call is delivered to a GSMsubscriber roaming in a TDMA/AMPS net-work.

The roaming GSM subscriber is reachedby calling his or her directory number (mo-bile station ISDN number, MSISDN). As-suming the call comes from the publicswitched telephone network (PSTN), it isrouted to the gateway mobile switching cen-ter (GMSC), whose task is to interrogate thesubscriber’s HLR in the home GSM networkto determine how the call is to be routed.Essentially, this involves asking the HLR fora routable number to which the call can bedelivered. In this example, since the GSMHLR previously received an update locationmessage from the Mobility Gateway thatserves as a GSM visitor location register(VLR), the HLR initiates a provide roamingnumber invoke message to the Mobility Gate-way. The Mobility Gateway then initiatesconveyance of the ANSI-41 equivalent mes-sage, which is called routing request invoke, tothe “real” serving MSC/VLR in theTDMA/AMPS network. The response to therouting request, which contains a routablenumber, is translated and sent back to theGSM HLR and transferred to the GMSC.With this information, the GMSC can de-

TDMA or dual-standard handset GSM subscription

Mobility Gateway

4

3

2

8

7

1

9

5

6

10

HLR

MSC/ VLR

GMSC

PSTN

GSM network

“VLR” “HLR” TDMA / AMPS network

Figure 3Call delivery to a GSM subscriber roamingin a TDMA/AMPS network.Key:1, 2 = Call3 = Send routing information invoke4 = Provide roaming number invoke5 = Routing request invoke6 = Routing request return result7 = Provide roaming number result8 = Send routing information result9 = Call delivery (voice trunk)10 = Mobile terminal call setup

AC Authentication center (TDMA)AMPS Advanced mobile phone serviceANSI American National Standards Insti-

tuteAUC Authentication center (GSM)CAS Customer administration systemCORBA Common object-request broker

architectureGMSC Gateway mobile switching centerGSM Global system for mobile communi-

cationHLR Home location registerILR Interworking location registerITU International Telecommunication

UnionMAP Mobile application partMSC Mobile switching centerMSISDN Mobile station ISDN number (Note:

the terms mobile station and mobileterminal are used interchangably.)

OA&M Operation, administration and main-tenance

PDA Personal digital assistantPSTN Public switched telephone networkSCP Service control pointSS7 Signaling system no. 7TDMA Time division multiple access (name

of products and services based onthe TIA/EIA 136 standard)

TMN Telecommunications managementnetwork

VLR Visitor location registerWAP Wireless application protocol

BOX A, ABBREVIATIONS

92 Ericsson Review No. 2, 1999

liver the call to the serving MSC in theTDMA/AMPS network.

Subscribers are thus able to have a singlesubscription and directory number for bothnetworks. This can be achieved even if twodifferent mobile terminals are used (one forGSM and one for TDMA/AMPS). Note:Dual-standard handsets offering GSM 1900and AMPS 800 are already being used in cer-tain markets.

For simplicity, the above examples haveonly shown the traffic scenarios of a GSMsubscriber roaming into a TDMA/AMPSnetwork. The Mobility Gateway also sup-ports roaming in the other direction fromTDMA/AMPS into a GSM network.

The Mobility Gateway consists of an in-terworking function that uses Jambala’s net-work signaling and traffic services to convertapplication-level messages (Figure 4); for ex-ample, update location to registration notifica-tion. The interworking function also popu-lates and maintains roaming subscriber pro-file data in messages received from the HLR

Jambala™ Mobility Gateway

Interworking function (IWF)

Network signaling services

GSM MAP ANSI/ITU SS7

ANSI-41 ANSI/ITU SS7

Traffic services OA&M basic services

OA&M function

Figure 4Components of the Mobility Gateway.

The article, Jambala—Intelligence beyond digi-tal wireless1, introduced the new Jambala appli-cation platform. The following is a summary ofthe Jambala application platform.

The JAMBALA application platform is builton years of extensive research in open sys-tems. The platform, which consists of Erics-son’s new TelORB operating system/middle-ware and a multiprocessor hardware platform,offers the following features suitable for real-time, fault-tolerant telecommunication appli-cations:• a multiprocessor execution environment;• a real-time, object-oriented execution envi-

ronment;• a fault-tolerant, real-time, memory-resident,

object-oriented database;• multiprocessor database distribution;• software fault tolerance through application

distribution;• zero-downtime software upgrade; • zero-downtime hardware upgrade;• a TMN-based OA&M model;• a CORBA 2.0-compliant interface for inter-

operability;• support for C, C++, and Java applications;• off-the-shelf hardware components;• N+1 hardware redundancy;• geographical redundancy; and• application platform resource scalability.

Automatic software error recoveryThe execution environment provides mecha-nisms for handling faulty code and erroneousdata that can lead to execution failures. Thesemechanisms ensure that execution failures are

automatically corrected or terminated withoutaffecting the operation of the network node. Thisis achieved by terminating individual processesrather than letting them hang.

Data fault tolerance and redundancyAll data is replicated; thus, if a processor goesdown, all data is accessed from its replicate.Once the processor is rebooted, all the data isre-transferred.

On-line backupThe application data, which is stored in the data-base, is log-marked for on-line backup at regular intervals. Backups can be performedautomatically by the backup scheduler or be initiated manually by a system administrator.When backup is initiated, application data iscopied to disk and sorted into files in a backuparchive partition of the file system. The hardwareplatform configuration is scaled to eliminate the effect of backups on application perfor-mance if additional hardware resources areused.

Adaptive hardware configuration When a processor board is added to the plat-form, the platform’s configuration managerautomatically reallocates its data and process-es to the new processor, according to the plat-form's configuration data. The configurationmanager monitors the platform's processorsand triggers the appropriate alarms, should afailure occur. It also attempts to recover theprocessor if a failure is detected. Recoveryinvolves the automatic reloading of processor

data and processes from replicas kept on otherprocessors.

Smooth software upgradeUpgrading software does not require any sys-tem downtime; the new version of the softwarecoexists with the incumbent version during soft-ware upgrades. The platform allows for the con-current execution of both old and new softwarein the same processor at the same time. All soft-ware processes that have to be executed whilean upgrade is being performed are allowed tocontinue using the old software, while all newprocesses are directed to the new software.

N+1 hardware redundancyRedundancy exists in signaling links, Ethernetswitches, O&M processors and all other hard-ware. Therefore there is no single point of fail-ure.

Hot-swappable hardware replacementHot-swappable hardware replacement allowsfor the smooth replacement of any hardwarecomponent. Hardware can be swapped withoutaffecting the system, thereby eliminating theneed to turn off the power.

Geographical node redundancyGeographical node redundancy allows a stand-by Jambala node to be deployed in a differentarea. The secondary node is capable of assum-ing the primary node’s functions in the event ofan active node failure, thereby ensuring that thefaulty node does not have any impact on over-all network performance.

BOX B, JAMBALA OVERVIEW

Ericsson Review No. 2, 1999 93

and serving MSC/VLR. Authentication mes-sages are passed from the Mobility Gatewayto the appropriate authentication centerfunctionality for the roaming subscribers.The authentication centers, TDMA AC andGSM AUC, are provided with the MobilityGateway and co-located with it on the Jam-bala platform. Several other advanced sub-scriber services, such as message waiting notification and short message service (SMS)are also supported through the MobilityGateway when subscribers roam into theother type of network.

The Mobility Gateway is a pure signalingnode, meaning that no voice trunks are con-nected to it. The two signaling systems in-volved are the ANSI SS7 and the ITU SS7(formerly called C7). It is possible to utilizeall four signaling and protocol combinationsor any subset thereof on the same MobilityGateway node:• GSM MAP over ITU SS7;• GSM MAP over ANSI SS7;• TDMA ANSI-41 over ITU SS7; and• TDMA ANSI-41 over ANSI SS7.The Mobility Gateway also includes an op-eration, administration and maintenance(OA&M) function that uses Jambala’s basicOA&M services to give the operator or cus-tomer administration system (CAS) the nec-essary capabilities to operate, monitor, andcontrol its operation.

Other JambalaapplicationsThe Mobility Gateway is one of many ap-plications developed on the Jambala appli-cation platform. A TDMA HLR and an au-thentication center have already been im-plemented. A TDMA service control point(SCP) is also being developed to offer intel-ligent network (IN) services.

An HLR is a database that handles sub-scriber data, which includes the service pro-file, location information, and activity sta-tus. The HLR also passes information on thesubscriber and the subscriber’s location toother network elements. An authenticationcenter is the network node required to au-thenticate mobile terminals. An SCP con-tains wireless IN service programs thatallow the operator to deploy customized ser-vices quickly. The software resident in theSCP functions as an interpreter for execut-ing service programs.

Furthermore, a wireless application pro-tocol (WAP) gateway is being developed.The WAP gateway is a network node that

serves as a bridge between the wireless net-work and the Internet. It converts and op-timizes Internet information to meet theunique constraints of current wireless trans-port and devices such as smart phones andpersonal digital assistants (PDA).

Multiple applicationsupportThe Jambala platform supports many dif-ferent applications that run concurrently onthe same Jambala node. For example, it ispossible to run the Mobility Gateway ap-plication concurrently with an HLR appli-cation. Indeed, there are no implicit limita-tions to the number of service offerings thatcan be run on the same platform. Limita-tions, if any, are indirectly dictated by traf-fic patterns (the number of transaction re-quests) and data use (memory capacity).

ConclusionEricsson’s Jambala Mobility Gateway ex-tends the boundaries of domestic and inter-national roaming by allowing inter-systemroaming—by means of the interworking lo-cation register functionality—betweenGSM and TDMA/AMPS networks.

The Mobility Gateway does not imposeany modifications on individual networkcomponents, such as HLRs and MSC/VLRsin current GSM and TDMA/AMPS envi-ronments.

The Mobility Gateway, which is a puresignaling node, consists of an interworkingfunction that uses Jambala’s network sig-naling and traffic services to convert application-level messages. Messages im-plemented in the Mobility Gateway con-form to TDMA/AMPS and GSM standards.The mapping of MAP and ANSI-41 proto-cols allows for the exchange of informationneeded to provide basic mobility manage-ment across different networks. Conse-quently, the protocols and interfaces associ-ated with service delivery in different net-works begin to look increasingly similar,even though the physical network elementsare different.

The Mobility Gateway uses Jambala’sbasic OA&M services, which gives the op-erator or customer administration systemthe necessary capabilities to operate, moni-tor and control its operation.

The advantages of the Jambala applica-tion platform are optimum scalability, mod-ularity, performance and cost-effectiveness.

1 Jones, F.: Jambala—Intelligence beyonddigital wireless. Ericsson Review Vol.75(1998):3, pp.126–131.

REFERENCES