165410762-rxi-ericsson

System architectureEricsson’s Internet protocol-based base sta-tion system (IP BSS) is built on a server-gateway architecture—that is, the networkelements that handle payload are separatefrom the servers that control traffic. Allswitching is handled inside the IP network.The IP BSS consists of five main parts (Fig-ure 1):• the radio network server (RNS);• the radio base station (RBS);• the BSS gateway (GW);• the real-time IP network; and• the operation and maintenance (O&M)

system, which includes subnetwork man-agement.

The introduction of IP does not give rise toany perceived functional changes to voiceand data services. The IP BSS supports stan-dard GSM services and air interface proto-cols, and connects to the core network viastandard ETSI and ANSI interfaces.

Functionality of the main parts

RNS

In the IP BSS, the radio network server han-dles all radio network logic and call control.By radio network logic, we mean the selec-tion of cells for mobile stations (MS) that arein active mode, and air-interface channels. The radio network server is responsible for • setting up and releasing connections be-

tween a mobile station and the mobile ser-vices switching center (MSC);

• coordinating the assignment of trafficchannels; and

• controlling handover. It also distributes paging to all cells that be-long to a location area (LA) or a base stationcontroller (BSC) area. No payload data isrouted through the radio network server.The IP network handles all switching, ormore correctly, routing. Other RNS func-tionality includes control of the gateway,optimization of performance data, and con-figuration of radio base stations.

For general packet radio service (GPRS), theradio network server allocates radio channelresources to be used by the radio base station.It is also responsible for the signaling entityto the serving GPRS support node (SGSN).The radio network server thus handles auto-configuration and negotiates user datagramprotocol (UDP) and IP endpoints relative tothe SGSN.

224 Ericsson Review No. 4, 2000

Ericsson’s IP-based BSS and radio network serverNiilo Musikka and Lennart Rinnbäck

The IP-based base station system (IP BSS) is designed to support bothGSM BSS and TDMA-EDGE (EGPRS-136) radio access networks. It pro-vides a future-proof path to the GSM EDGE radio access network(GERAN), since it has been optimized to handle a mix of data (GPRS andEDGE) and real-time services, such as voice traffic.

The authors describe the architecture of the IP BSS, the main function-ality of the network elements, and the salient features of this new radioaccess solution.

3GPP Third-generation Partnership ProjectANSI American National Standards InstituteAPI Application program interfaceAU Application unitBSC Base station controllerBSS Base station systemBSSAP BSS application partBTS Base transceiver stationCIC Circuit identity codeCM Configuration managementCMH Connectionless message handlerCORBA Common object request broker

architecturecPCI Compact peripheral component

interconnect CRM Cell resource managerDHCP Dynamic host configuration protocolDiffServ Differentiated servicesDSCP Differentiated services code pointDTX Discontinuous transmissionEDGE Enhanced data services for global

evolutionEEM Embedded element managerEM Element managerETSI European Telecommunications

Standards Institute

FM Fault managementGEM Generic Ericsson magazineGERAN GSM EDGE radio access networkGO Global objectGPRS General packet radio serviceGSM Global system for mobile

communicationGW GatewayHDLC High-level data link communicationIP Internet protocolIRP Integration reference pointJ2SE Java 2 standard editionJNDI Java naming and directory interfaceJVM Java virtual machineLAN Local area networkMAC Media access controlMGW Media gatewayMIB Management information baseMIM Management information model MO Managed objectMPPP Multilink PPPMS Mobile stationMSC Mobile services switching centerNLS Name lookup serviceNM Network management systemO&M Operation and maintenance

OS Operating systemPDH Plesiochronous digital hierarchyPHB Per-hop behaviorPM Performance managementPPP Point-to-point protocolQoS Quality of serviceRBS Radio base stationRFC Request for commentsRLC Radio link controlRNS Radio network serverSCB-RP Support and connection boards with

integrated regional processorsSCCP Signaling connection control partSGSN Serving GPRS support nodeSNM Subnetwork managerSS7 Signaling system no. 7STM Synchronous transfer modeTCP Transmission control protocolTDMA Time-division multiple accessTRC Transcoder controllerTRX TransceiverUDP User datagram protocolUMTS Universal mobile telecommunications

systemUTRAN UMTS terrestrial radio access networkWAN Wide area network

BOX A, ABBREVIATIONS

Ericsson Review No. 4, 2000 225

RBS

The radio base station, which includes radiotransmission and reception functions for theair interface, is controlled by the RNS whenvoice calls are set up to mobile stations. Theactual voice frames are sent directly to thetranscoder in the gateway. Basic softwareand hardware parameters are set in the op-eration and maintenance system. Faults thatoccur on circuit boards and other explicithardware are reported directly to this sys-tem. Apart from reports on lost capacity, no reports are made to the radio networkserver.

The radio network server orders the con-figuration of the physical resources that rep-resent a cell. To handle the GPRS/EDGEpacket service, the radio base station in-cludes radio link control (RLC) and mediaaccess control (MAC), which manage pack-et data traffic to and from the SGSN andmobile stations. The radio base station alsoincludes an embedded IP router which dis-tributes packets internally and which can beused for connecting several radio base sta-tions in a cascading configuration.

BSS gateway

The gateway is composed of a media gate-way and a signaling system no. 7 (SS7) gate-way. The media gateway • is responsible for pools of transcoders that

handle speech and circuit-switched dataservices;

• participates in handover; and • connects transcoders to a particular cir-

cuit on the A-interface. On request by theradio network server, a resource managerin the media gateway allocates resourcesand sets up or switches connections.

The SS7 gateway handles SS7 signaling tothe mobile services switching center anddistributes BSS application part (BSSAP)messages to the correct entity (processor) inthe radio network server. The transmissioncontrol protocol/Internet protocol (TCP/IP)is used for the signaling of BSSAP messagesbetween the SS7 gateway and the radio net-work server. The O&M system is used forloading software into and configuring thegateway building blocks.

O&M system

The O&M functionality is built into dedi-cated subnetwork managers (SNM) and thenetwork elements (Figure 2). Each networkelement thus includes its own element man-ager. TCP/IP is used for all managementcommunication. Several means of commu-

nication are provided for the communica-tion between network elements and theO&M system—for example, the network el-ements contain Web pages that can be readby any browser with the appropriate accessrights. A command line interface has alsobeen provided.

Subnetwork management

OSS

RNS

ILM

MSC

SGSN

A

Gb

RBS

RBS RBS

RBS RBS

BSS gateway

Radio control

IP network

Figure 1System architecture.

RBS

EMRNS

EMRXI 820

EMDXX/

MINI-LINK

EMGW

EM

SNM for RAN mgmnt

SNM for IP layer

mgmnt

SNM for transmission

mgmnt

Client

ClientClient

NMS

IP network

Figure 2Operation and maintenance system.

The element managers interwork with thesubnetwork manager over an interface thathas been based on the common object re-quest broker architecture (CORBA). Thesubnetwork manager can integrate raw frag-mented performance data into a single co-herent picture for presentation to the oper-ator.

Apart from the radio base stations, whosecell parameters are configured by the radionetwork server, all network elements areconfigured by the O&M system or by them-selves. Subscriptions between a network el-ement and the subnetwork manager can beset up to have the network element provideevents that enable the keeping of real-timestatistics. This capability can be used to ob-tain an overview of the number of calls percell, or for local troubleshooting.

The IP BSS is simple to install and facil-itates the deployment of numerous nodes.• When the network element is connected

to the transmission network it begins de-tecting transmission parameters. It thenconfigures itself (layers 1 and 2) accord-ingly.

• An IP connection can then be establishedbetween the network element and the IPnetwork. The network element commu-nicates with IP network servers to obtainIP addresses and other data that enable itto communicate over the IP network.

• Finally, the network element is config-ured according to the specified radio net-work plan (that is, it downloads cell pa-rameter settings, such as frequency andpower levels).

The O&M system includes an IP layer man-agement function that is used for manag-ing the IP network. IP network implemen-tations for wireless systems are composed of

numerous nodes, either stand-alone or em-bedded in radio base stations. To addressthe need for cost-effective, large-scale man-agement, Ericsson has developed the IPlayer manager1, which includes support forthe automatic configuration of large-scaleIP-based mobile networks. It also includesa sophisticated means of managing IP net-work performance, in order to support end-to-end real-time sessions for delay-sensitiveapplications and signaling.

Real-time IP network

The IP network handles all routing in thesystem. Quality-of-service (QoS) properties(differentiated services, DiffServ) permitreal-time traffic to be carried with mini-mum delay. If differentiated services cannotbe provided, then bandwidth must be di-mensioned to provide minimum delay forreal-time traffic. The IP network uses real-time IP routers that have been optimized forthe requirements of wireless data and voicetraffic.1 Ericsson’s RXI 820 real-time routerwas designed specifically to meet the re-quirements in this part of the network.

Simple traffic case: call to a mobilestationA paging command arrives over the A-in-terface to the SS7 gateway. The completeSS7 stack is terminated in the gateway (theRNS does not need to include an SS7 stack)and the paging command is sent via TCP/IPto the radio network server, which distrib-utes the paging command to the appropri-ate radio base stations (Figure 3).

A radio base station detects a channel re-quest and signals the radio network server.The radio network server selects a dedicat-ed radio channel and directs the mobile sta-tion to it. The radio network server also sig-nals to the SS7 gateway, instructing it to setup a signaling connection control part(SCCP) connection to the mobile servicesswitching center.

The mobile station then starts sendingmeasurement reports over the dedicatedchannel. The radio base station forwardsthese measurement reports to the radio net-work server and sends its own measurementsfor further evaluation.

The mobile services switching center as-signs a circuit identity code (CIC) on the A-interface and signals this to the radio net-work server (via the SS7 gateway), which in-structs the media gateway to allocate atranscoder. The media gateway connects thetranscoder to the CIC. The radio network


GW

SS7GW

Signaling Payload

MGW

MSC

IP

RBS

RNS

Figure 3Traffic case: call to a mobile station.


server also informs the radio base station andtranscoder of their counterparts’ IP address-es. The call can now be exchanged.

Operator benefits

System architecture

The IP BSS architecture has been designedto handle third-generation real-time multi-media services, GPRS and EDGE, and voiceover IP. It can be connected to a second-generation core network via A and Gb in-terfaces, and to a third-generation core net-work via Iu (UTRAN) interfaces. The IPBSS thus constitutes a big step toward thewireless Internet and all-IP networks.

The server-based architecture separatescontrol from payload, which means that eachplatform has been tailored to specific needs.The radio network server is a control nodeand the gateway handles payload.

The simplicity of traditional connection-less IP technology makes for efficient trans-port of packets, since no signaling is need-ed for setting up connections.

TransmissionThanks to its layered structure, the IP par-adigm offers a great degree of flexibility. In-deed, any physical and link layer technolo-gies can be used. Therefore, new, optimizedlink layer technologies can be introducedwithout affecting the application softwareof the IP BSS.

By using IP, it is possible to dimensionbandwidth according to actual traffic insteadof by peak allocation. In terms of transmis-sion, this yields significant savings, espe-cially for bursty GPRS or EDGE traffic aswell as for voice traffic that is transmitted bymeans of discontinuous transmission (DTX).

The embedded routers in the radio basestation and stand-alone routers at hub sitescan yield additional savings in transmission.A router can be used as an aggregation de-vice by• aggregating traffic from several trans-

ceivers in the embedded router in theradio base station; and

• aggregating traffic from several radio basestations in a hub site.

Depending of the extent of aggregation, thesubsequent bandwidth requirement is lessthan the sum of the individual links fromthe radio base stations. Routers can be usedinstead of remote base station controllers.The scheduling of differentiated services (inthe routers) differentiates traffic according

to priority, which further increases the useof the links.

The management of transmission in theradio access network can also be simplified:instead of managing individual plesiochro-nous digital hierarchy (PDH) timeslots, thebandwidth in the BSS network can be ex-tended independently of transceivers(TRX). If a good performance-monitoringtool is used, new transceivers can be com-missioned at radio base station sites with-out having to coordinate this action with ex-tensions of the transmission network.

Other IP-based services can easily be con-nected to the same access network—for in-stance, to use spare capacity and reducecosts. However, care must be taken to guar-antee the quality of service of the radio ac-cess network.

O&MThe distributed Web-based operation andmaintenance architecture ensures accessi-bility and user-friendliness with fewer inter-node dependencies. The operator can accessany radio base station, radio network serv-er, or gateway from any terminal. Since eachradio base station has its own IP address, itis possible to connect to it directly, to de-termine the cause of a problem.

A local area network (LAN) for operationand maintenance has been introduced at theradio base station site. The LAN is an Eth-ernet connection from the embedded routerin the RBS for connecting other site equip-ment that implements its own IP-basedO&M. To minimize the cost of installationand operation, all IP BSS products supporta high level of plug-and-play functionality.

During low traffic hours, greater band-width is available for operation and mainte-nance. Indeed, the entire bandwidth can beused for O&M signaling when traffic is low.At night, for example, excess capacity canbe used for downloading software to radiobase stations.

For fault and performance management,the operator can define filters and subscrip-tion functions to specify the kind of data eachnetwork element is to send to the subnet-work manager. This is particularly useful formonitoring certain network elements.

Integration reference points (3GPP orEricsson-specific) are used for communica-tion from the subnetwork manager to thenetwork management system. All configu-ration data is stored in the network ele-ments, thereby ensuring that the data is al-ways up-to-date and consistent. Copies of

the data are not kept at other parts of theO&M system. If required, however—for im-proved performance, or for some other rea-son—data can be cached in the subnetworkmanager.

IP transport

The challengeThe characteristics of the radio access net-work for GSM base station systems andTDMA-EDGE are as follows:• A large amount of traffic is delay-

sensitive, real-time voice traffic. This traf-fic is transferred in small packets of ap-proximately 35 octets, where each packetincludes one speech frame. Packets thatcontain best-effort data are normallymuch larger (greater than 500 octets).

• The bandwidths available on links in theradio access network—especially in thelast few kilometers to radio base sta-tions—are very low (less than 1.5 to 2Mbit/s). In many markets, these links arealso expensive to lease.

• A typical radio access network consists ofseveral hundred radio base stations, eachof which must have a stable network syn-chronization clock in order to fulfill thestringent requirements for generatingradio frequencies.

The solutionEricsson’s solution for the IP BSS features • quality-of-service differentiation by delay

and drop priorities (differentiated servicesarchitecture);

• low delay, thanks to the use of homoge-nous packet sizes (long packets are brokendown into smaller fragments by means ofthe multilink point-to-point protocol,MPPP);

• bandwidth efficiency using TCP/UDPheader compression;

• policing—overflow traffic is discarded;and

• IP layer management with a high degreeof automation for configuration manage-ment and performance monitoring.1

Quality-of-service differentiation

The IP BSS network handles several flowsof traffic streams (compressed speech,GPRS, traffic signaling, and network sig-naling). Because the nature of each trafficstream is unique, each stream must be for-warded independently in the networknodes. Accordingly, the IP BSS networkuses differentiated services, as defined inRFC 2475. In a DiffServ network, therouters forward the packets of different traf-fic streams according to the per-hop behav-ior (PHB) assigned to the packets. A differ-entiated services code point (DSCP) in theIP header of each packet (Figure 4) indicatesthe per-hop behavior.

The applications that generate IP pack-ets mark them with a DSCP according tothe level of service that the application re-quires. The metering, dropping and sched-uling are optimized in the routers to givegood voice service and to maximize the useof available bandwidth resources. For in-stance, a large part of the bandwidth can beallocated to operation and maintenancewhen no higher-priority end-user servicesare in progress.

Operators can configure the mapping ofend-user service classes into queues. How-ever, the service classes for internal IP BSSfunctions cannot be configured.

Low delay using homogenous packet sizes

On narrowband links, long packets must bebroken into smaller fragments, in order tokeep speech packets from being delayed.The packets are broken into fragments atthe link layer, using the multilink PPP(Figure 5).

If more than one DiffServ class must befragmented, the multilink PPP can be com-plemented by the MPPP multiclass exten-sion, to give optimal separation betweenfragmented quality-of-service classes.


IdentificationFlags

Fragment offset

Protocol

Time to liveSource address

Destination address

Options

Padding

Header checksumVersion IHL

CUDSCP

Total length

0

01

02

03

Figure 4IP header.


Bandwidth efficiency using TCP/UDPheader compression

The UDP/IP header (28 octets) must becompressed to obtain efficient transmission.UDP/IP header compression reduces theheader to just 5 to10 octets, including PPPand high-level data-link communication(HDLC) overhead. The header compressiontechnique is described in RFC 2507.

Policing—discarding overflow traffic

At the edge of the DiffServ IP network,traffic is grouped into quality-of-serviceclasses. The traffic is also compared to de-fined traffic contracts, to determine if it isto be admitted into the network. How-ever, as relates to the base station system,all applications that send traffic into thenetwork from base stations or gateways aretrusted. The role of traffic contract mech-anisms can thus be reduced to that of han-dling error cases. Each defined traffic-generating unit (such as a radio base sta-tion) is allocated a maximum bandwidththat it may never exceed.

Homogenous implementation of real-time routers in the IP networkEricsson is implementing the same real-time router technology throughout the IPnetwork to guarantee that delay-sensitiveservices are handled in an optimized fash-ion. Besides the stand-alone RXI 820, Ericsson’s real-time router is embedded in

the base station. In subsequent releases, itwill also be embedded in gateways. This ho-mogenous implementation of real-timerouters in the IP network guarantees opti-mized end-to-end real-time performance.Similarly, it allows for • a homogenized O&M solution for all IP

components; and• rapid deployment of new functionality—

by means of simultaneous network-widesoftware upgrades—without affecting in-teroperability.

Where interworking relates to other man-ufacturers’ routers, a distinction must bemade between interoperability and real-time performance: interoperability is astandards issue, whereas real-time perfor-mance is dependent on the implementa-tion. Ericsson’s solution, which is fullybased on open industry standards, guaran-tees end-to-end real-time performancewithout introducing weak links into therouter chain.

MigrationEricsson’s current base station system can beupgraded to become an IP BSS. The upgradeconsists of • introducing the radio network server;• introducing a new interface board for IP

into the RBS 2000; and • upgrading the base station controller and

transcoder controller (BSC/TRC) to work

PPP only

PPP + MPPP

Incoming traffic PPP layer scheduler

Outgoing traffic

Max voice delay

Max voice delay

Incoming traffic PPP layer scheduler

Outgoing traffic

Voice

Video

Data

2

3

1

2 4

3

1

Voice

Video

Data

Figure 5 Fragmentation.

as a gateway and to enable it to connectto the IP network.

The combined BSC/TRC (Figure 6) func-tions as a gateway to IP-enabled radio basestations and radio network servers, and as anordinary BSC/TRC for radio base stationsthat use synchronous transfer mode (STM).In a subsequent release, the gateway func-tionality will be implemented on the Cellopacket platform used in Ericsson’s third-generation mobile networks.2 Operators ofan Ericsson base station system can thusreuse a large part of their installed equip-ment when they upgrade to the IP BSS. TheO&M system is the same for both the IP BSSand current base station systems.

The radio network serverThe structure of the radio network server isdivided into three main layers with subor-dinate layers: • application software;• system software; and• hardware platform. In general, a higher layer is solely dependenton the services provided by the layer imme-

diately below it. The RNS applications aredependent on the services provided by theapplication program interface of the systemsoftware platform. The number and type ofprocessors and the means of inter-processorcommunication are hidden from the appli-cations.

BenefitsThe radio network server is based on Ericsson’s TSP server platform. Thanks toindustry-standard operating systems,processor boards, and components, thisplatform can quickly be adapted to newtechnologies. The use of common APIs andindustry-standard development languagesensure openness, portability, and the abili-ty to incorporate sourced components. Thesystem software and Solaris operating sys-tem constitute the execution environment.The system software hides the underlyingprocessing architecture from applications.The software can be upgraded during oper-ation.

The hardware platform consists of a clus-ter of high-performance processors. Thephysical infrastructure of subracksequipped with processor boards and dupli-cated Ethernet switches provides scalabili-ty and high availability. All boards can beswapped (hot swapping) while the systemis in operation. The radio network server isa robust and fault-tolerant system that hasbeen designed especially for telecom appli-cations. The application is divided intosmall software units that are distributedover the processing platform. This modu-lar approach gives operators flexibility inconfiguring for different network scenarios.The dynamic distribution of load makes forefficient use of processing resources. If oneprocessor fails, the affected applicationunits are restarted quickly on other proces-sors, which effectively means non-stop op-eration.

Hardware platformThe hardware platform is based on thegeneric Ericsson magazine (subrack) withtwo support and connection boards with in-tegrated regional processors (SCB-RP). Theboards are equipped with Ethernet switch-es. Via the backplane, processors are con-nected to the Ethernet switches for dupli-cated 100 Mbit/s inter-processor communi-cation (Figure 7). The switching hierarchyhas two levels. The SCB-RP boards withlevel-1 switches are placed at each end of asubrack. The level-2 Ethernet switches in-


RBS

RBS

BSC/TRC (AXE)

RNS

NMS/SNM

MSC

SGSN

RBS upgraded to IP

New RBS for IP communication

RBS with STM communication

SGSNGb (IP)

Gb (FR)

A (PCM)

A (SS7)

RBS RBS

RBSRBS

RBS

Figure 6Evolution of the base station subsystem.


terconnect the subracks by means of1000Base-T links in a star configuration.

Besides the switches, each subrack con-tains interface boards for external commu-nication and various processor boards. Thesmallest configuration is composed of a single subrack—this configuration can be expanded to encompass several subracks.The interface boards have 100Base-Tx linksto the external router (RXI 820), which haswide area network (WAN) interfaces for connecting to other IP BSS nodes. Thenumber of interface boards is dependent on the bandwidth needed for external sig-naling.

The processor boards are composed of UltraSPARC cPCI boards attached toadapter boards that provide electrical andmechanical conversion to the GEM back-plane. Two processors serve as node controlboards (one active and one in standby mode).Likewise, one processor per subrack servesas the boot server. Apart from these, all otherprocessors are diskless.

The dual –48V DC power feed is distrib-uted via the SCB-RP boards to the back-plane. The voltage is converted on eachboard according to its specific level andpower requirements. All boards supporthot-swapping capabilities. The GEM sub-racks are stacked in a standard Ericsson BYB 501 cabinet.3

System softwareThe structure of the software platform hasbeen divided into multiple layers (Figure 8).The bottom layer consists of the Solaris op-erating system.

The radio network server, which hasmainly been developed in Java, exploits theversatility of the Java 2 standard-edition(J2SE) platform—that is, it includes sup-port for concurrency, distribution, memorymanagement, code loading, and IP com-munication.

On top of the Java 2 platform, various soft-ware platform services have been partitionedinto an execution control layer, an interac-tion layer, and a system services layer.

The coordination layer manages threads,queues jobs, detects deadlocks, and protectsagainst overload.

Execution control layer

The execution control layer, which usessome of the services provided by theRonja/DPE middleware4, gives the applica-tion layer functions for high availability, ina way that minimizes impact on the appli-

cation. The applications execute on a virtu-al machine and are unaware of the underly-ing processing architecture. The executioncontrol layer provides the following services: • applications can be divided into smaller

application units (AU), which can easilybe deployed in various combinations onmultiple processors;

• takeover—to achieve a dynamic distribu-tion of load between processors, the ap-plication units can be moved from oneprocessor to another during operationwithout disturbing traffic;

• upgrades—the application units can beupgraded during operation and withoutdisturbing traffic; and

• failover—failed units are restarted withminimal disturbance to traffic. If a proces-sor fails, all affected application units arerestarted on other processors.

Interaction layer

The interaction layer provides the applica-tion layer with a high-level communicationinterface that makes the application inde-pendent of the communication mechanismin use.

Level 1 Ethernet switch



100Base-Tx links to external networks

1000Base-T links for subrack interconnection

Interface board

Adapter

-48V-48V

UltraSPARC cPCI processor boardsLevel 2 Ethernet switch boards

Subrack 1

Subrack 2

Subrack 3

Figure 7Hardware platform structure of the radio network server.

Application software

Hardware platform

Coodination layer

J2SE

OS

Execution control layer

Interaction layer

System services layer

Figure 8Layers of the software platform.

The interaction layer handles sockets andthreads, and contains functions for encod-ing and decoding messages.

For internal RNS communication, the in-teraction is proxy-based (Figure 9). Differ-ent application units interact by means ofglobal interfaces implemented by global ob-jects (GO). The interaction layer providesthe mechanisms that an application unitneeds to invoke methods on a global objectin another application unit, regardless ofwhether or not the application units are lo-cated on the same processor (JVM). Theglobal object is found by means of a namelookup service (NLS).

Depending on the interface, several dif-ferent protocols are used for external com-munication. The interaction layer estab-lishes a logical connection between an RNSprocessor and an external node for ex-changing asynchronous messages. Thephysical connection is hidden from the ap-plication.

System services layer

The system services layer consists of a nam-ing service, logging service, timer service,and persistence service. The persistence ser-vice ensures that the configuration and traf-fic data persist and survive failures. The ap-plication unit actively saves its state to thesystem services layer, which replicates thestate onto another processor. During failovera new application unit is created on thestandby processor and its state is restoredfrom the system services layer.

The naming service, which is based on the standard Java-naming-and-directory-

interface (JNDI) API, uses Jini lookup inthe name lookup service (NLS). The namelookup service enables application units toestablish contact with one another regard-less of their locations.

Thanks to the NLS, the physical locationsof different resources remain hidden fromthe application layer. Instead, logical namesare used. These names do not change whenthe application units are moved to new lo-cations.

RNS application architectureThe structure of the application software isdivided into two main layers (Figure 10):• the GSM application contains different

kinds of application unit; and• the operation-and-maintenance applica-

tion contains an embedded element man-ager (EEM).

Additional applications can be located onthe same layer as the GSM application. Dif-ferent application configurations can beused.

GSM application

The GSM application controls circuit-switched connections in IP BSS networks. Italso handles common signaling (such as pag-ing) to a mobile services switching center orSGSN.

The cell resource manager (CRM) appli-cation unit serves every function that is re-lated to a single cell—there are as many ap-plication units as there are cells served bythe radio network server. The connection-less message handler (CMH) handles func-tions that are common to several cells. Forexample, the radio network server can serveone or more logical base station con-trollers—one CMH per BSC—which im-plies that a high-capacity radio networkserver can interwork with several MSCs orSGSNs.

The division of the GSM application intocell resource managers is the basis for dis-tributing load dynamically (takeover). Acell application unit can be upgraded orrestarted independently of other cell appli-cation units. The division of the GSM ap-plication into small autonomous cell appli-cation units is a foundation for very highavailability. Most messages are routed di-rectly between a cell application unit (cellresource manager) and the interaction layerwithout passing a central point, which fur-ther improves robustness. The GSM root(Figure 10) contains functions for creatingor restarting application units, and controls


All SPARC trademarks are used under licenseand are trademarks or registered trademarksof SPARC International, Inc. in the UnitedStates and other countries. Products bearingSPARC trademarks are based upon an archi-tecture developed by Sun Microsystems, Inc.

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TRADEMARKS

A B

C' C''B''B'

Application layer Application layer

Interaction layer

Proxy Dispatcher DispatcherProxy

AU AU

GOC

GO

AU

JVM JVM

Interaction layer

Figure 9Internal communication of the radio network server via the interaction layer.


takeovers and upgrades. The cell resourcemanager is responsible for • setting up and releasing connections be-

tween mobile stations and the mobile ser-vices switching center;

• assigning traffic channels; and • media gateway interworking. Each cell contains a pool of radio resourcesand an algorithm that allocates logicalchannels. Measurements from serving andneighboring cells are received by the locat-ing algorithm, which determines handover.The source and target CRM applicationunits interwork for handovers betweencells.

Element management

The embedded element manager, which isresponsible for the operation and mainte-nance of the RNS node (network element),serves the subnetwork manager client via aninterface that is based on CORBA. It canalso serve a thin client through a Web in-terface. The embedded element manager isan application unit that interworks withother application units in the GSM applica-tion.

The embedded element manager containsapplications for configuration management(CM), fault management (FM), performancemanagement (PM) and self-management.The configuration management part han-dles the configuration of radio network pa-rameters. It is based on a management in-formation model (MIM) that describes • classes with attributes; and • relationships between classes. The configuration management part alsocontains a management information base(MIB) with managed objects (MO) that areinstances of classes defined by the manage-ment information model.

The performance management part mon-itors, records, and supervises performanceaccording to notifications received from theapplication units. The performance-monitoring function handles statistics gath-ered from counters and gauges; the perfor-mance-recording function handles events;and the performance-supervision functiondefines thresholds for a gauge—when thethreshold is exceeded, it generates an alarm.

The fault-management part handlesalarms, keeping a list and log of alarms.

The self-management part contains • a hardware inventory—which includes

the status of the RNS hardware; and• a software inventory—which is used for

managing software.

ConclusionThe IP-based base station system (IP BSS),which is built on a server-gateway architec-ture, is designed to support both GSM BSSand TDMA-EDGE (EGPRS-136) radio ac-cess networks. The solution features quali-ty-of-service differentiation, low delay,bandwidth efficiency (using TCP/UDPheader compression), policing, and IP layermanagement with a high degree of au-tomation for configuration managementand performance monitoring. The IP BSSconsists of • an RNS, which handles all radio network

logic and call control;• an RBS, which includes radio transmis-

sion and reception functions for the air in-terface. The RBS is controlled by the RNSwhen voice calls are set up to mobile sta-tions. The actual voice frames are sent di-rectly to the transcoder in the gateway;

• a BSS gateway, which is composed of amedia gateway and a signaling system no.7 (SS7) gateway—the media gateway isresponsible for pools of transcoders thathandle speech and circuit-switched dataservices. It participates in handover, andconnects transcoders to a particular cir-cuit on the A-interface.

• a real-time IP network—all switching ishandled inside the IP network; and

• an O&M system—the O&M functionali-ty is built into dedicated subnetworkmanagers and network elements. Eachnetwork element includes its own ele-ment manager.

Ericsson’s current base station system can beupgraded to become an IP BSS.

1 Börje, J., Lund, H-Å. and Wirkestrand, A.:Real-time routers for wireless networks.Ericsson Review Vol. 76 (1999):4, pp. 190-197.

2 Reinius, J.: Cello—An ATM transport andcontrol platform. Ericsson Review Vol.76(1999):2, pp. 48-55.

3 Stockman, B. and Wallers, A.: The BYB 501metric equipment practice. Ericsson ReviewVol. 74(1997): 2, pp. 62-67

4 Karlson, M.: Ronja—A Java application plat-form. Ericsson Review Vol.77(2000):4, pp.244-247.

REFERENCES

Operation and maintenance application OM

root

1 per RNS

1 per RNS 1 per BSC 1 per cell

GSM root

Radio network config

Connection- less

message handler

Cell resource manager

Embedded element manager

GSM application

Figure 10Layered application architecture.

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