A MANAGEMENT ARCHITECTURE FOR ENABLING WIRELESS SYSTEM OPERATION IN THE B3G CONTEXT AND EXPLOITATION OF THE ABC CONCEPT

Transcription

1 A MANAGEMENT ARCHITECTURE FOR ENABLING WIRELESS SYSTEM OPERATION IN THE B3G CONTEXT AND EXPLOITATION OF THE ABC CONCEPT Artemis Kutsrdi 1, Vera Stavrulaki 1, Panagitis Demestichas 1, 2, Niks Kutsuris 1, Gerge Kundurakis 1, Dimitris Kuis 1, Niklas Mitru 1 1 Natinal Technical University f Athens, Schl f Electrical and Cmputer Engineering 9 Irn Plytechniu St., Zgraphu Athens, Greece 2 University f Piraeus, Department f Technlgy Educatin and Digital Systems Piraeus, Greece artemis@telecm.ntua.gr, vera@telecm.ntua.gr, pdemest@unipi.gr, nkutsuris@telecm.ntua.gr, gkund@telecm.ntua.gr, kuis@telecm.ntua.gr, mitru@sftlab.ntua.gr Abstract: This paper presents a management architecture that enables wireless systems t perate in the Beynd 3G cntext, while allwing users t benefit frm the Always Best Cnnected cncept. It fcuses n the structure and functinality f a general netwrk and service management system fr hetergeneus wireless access netwrks, capable f ptimising service delivery and traffic lad distributin in cmpsite radi envirnments. Aspects cncerning the cmmunicatin between the user terminals and this management system receive special attentin. A test case where the validity f this management architecture s functinality is verified, and cnsequent results, are als presented. 1. Intrductin The evlutin f wireless cmmunicatin systems ver the past years demnstrates a clear trend twards architectures that will supprt multiple radi access technlgies and types f terminals, and that will incrprate functinality fr the supprt f the Always Best Cnnected cncept. The latter allws a persn cnnectivity t applicatins using the devices and access technlgies that best suit his needs, thereby cmbining the features f access technlgies, such as WLAN, with cellular systems, such as UMTS, in rder t prvide an enhanced user experience fr 3G and beynd. A challenging issue related t the abve is the develpment f a management framewrk that will enable ptimal system peratin, thus allwing users t enjy high-quality wireless services in a seamless way. This paper is structured as fllws: The secnd sectin defines and discusses the B3G and ABC cncepts. The third sectin intrduces a management architecture fr enabling the realizatin f these cncepts in a cmpsite radi system, and utlines its main mdules. The furth and fifth sectins elabrate n the functinality f the Sessin and the Netwrk mdules f the management system respectively. The sixth sectin presents a test case and results that serve t check the validity f this management architecture s functinality, and the final sectin cncludes the paper. 2. Beynd 3G and Always Best Cnnected cncepts The next generatin f mbile systems is expected t cmprise hetergeneus netwrks cnsisting f diverse radi segments, able t hst multimde wireless terminals, each f them capable f alternatively perating in each f the diverse radi segments available in the infrastructure. The different radi segments, r access technlgies (e.g. WLANs, cellular and bradcast netwrks), will be intercnnected by a backbne (e.g. an IP-based fixed netwrk) and jintly perated in an ptimized fashin that will allw fr an imprved verall resurce management and netwrk resurce prvisining in reply t requests frm the different service prviders. These ptimisatin pprtunities will increase the feasibility f prviding advanced QS-aware cntent services t the users f the multimde terminals ver the cmpsite netwrk. It is clear that the mst salient feature f these evlving systems will be the multiplicity f access technlgies and terminals, that will allw users t enjy wireless services at any time, at any place. This cnstitutes the always best cnnected (ABC) cncept: being cnnected at any pint in time t the best available access netwrk. The latter is defined as the netwrk that best suits the user s needs at that particular mment and may be a functin f the user s persnal preferences, f the different peratr s plicies and business agreements and f the infrastructure s available netwrk resurces. The applicatin f the ABC cncept t an envirnment f multiple access technlgies allws fr the beneficial cmbinatin f the cverage f cellular and bradcast This wrk is partially funded by the Cmmissin f the Eurpean Cmmunities, under the Fifth Framewrk Prgram, within the IST prject CREDO (IST : Cmpsite Radi and Enhanced Service Delivery fr the Olympics).

2 systems with the flexibility and high bandwidth f WLAN systems. In this cntext, the explitatin f the cmpsite radi infrastructure requires an innvative Netwrk and Service Management System (NSMS), capable f driving the user terminals t the apprpriate quality level and netwrk fr each service, in a transparent manner. Figure 1 depicts a general cmpsite radi architecture that includes such a management cmpnent. Service and Cntent Prviders Netwrk and Service Management System IP-based Fixed Netwrk Radi Netwrks Cmpsite Radi Envirnment Netwrk Infrastructure Terminal Statins Figure 1. Main cmpnents in a cmpsite radi architecture. 3. Management architecture fr enabling the B3G and ABC cncepts Optimal system peratin is t be achieved thrugh the jint cntributins f bth the netwrk and the terminals: On the netwrk s side, the NSMS will perfrm tasks such as the balancing f the traffic lad between the different radi segments, and the general crdinatin theref the gal being ptimal jint resurce management. In mre detail, the NSMS shuld be capable f mnitring and analysing the perfrmance and the QS levels prvided by the different netwrk elements, f dynamically calculating and impsing the ptimal traffic lad distributin, and f inter-wrking with the user terminals. Figure 2 depicts the main mdules f the NSMS entity, that carry ut the abve-mentined tasks, namely the Sessin and the Netwrk. NSMS structure Sessin Terminals Netwrk Managed netwrks Figure 2. Main mdules f the netwrk management cmpnent (NSMS). The Sessin addresses a shrt-term ptimisatin prblem, targeted t the assignment f the user terminal t a specific netwrk, thus enabling the selectin f the apprpriate radi technlgy thrugh which services can be btained efficiently in terms f cst and QS, in near real time. The Netwrk, n the ther hand, addresses a mid-term ptimisatin prblem, targeted t the splitting f the aggregate traffic lad t the underlying netwrks, and t the assignment f traffic t QS levels. On the terminal s side, a Terminal Statin Management System (TSMS) that will interact with the NSMS is required. The purpse f that interactin will be making the ptimal selectin f the apprpriate radi segment t which the terminal will eventually be assigned. This interactin will als ensure that the netwrk s and the terminal s estimate f radi cnditins and QS levels in the system are beneficially cmbined fr making an educated selectin f the apprpriate radi technlgies thrugh which services can be btained as efficiently as pssible. Thus, bth the netwrk and the terminals cntribute intelligence twards ptimal system peratin. The interactin between the TSMS and the NSMS is nt expected t be limited t the initial radi selectin, but will rather be maintained thrughut the entire stay f the terminal in the cmpsite radi envirnment. The purpse f this cmmunicatin will be the handling f events riginating either frm the terminal, such as requests fr the prvisin f additinal services, infrmatin regarding the radi cnditins in the area r the QS levels assciated with the services currently running n that terminal, r frm the netwrk, such as the re-distributin f terminals acrss radi segments fr the purpse f balancing the verall lad. Bth kinds f events may result in terminals being subject t a vertical handver. Anther ntewrthy feature f this apprach is the supprt f advanced QS-aware services. It is assumed that the users f the cmpsite netwrk will have access t advanced IP-based services, btained thrugh applicatin client sftware running n tp f the wireless terminals and accessing cntent frm applicatin servers ver the netwrk. These services will be ffered at multiple QS levels. The accessibility t a service and its particular QS level will be determined by the user s prfile. The fllwing sectins discuss the functinality f the Sessin and the Netwrk f the NSMS in mre detail. 4. The Sessin Μanager 4.1. Functinality fr supprting the ABC cncept In an envirnment f multiple access technlgies, where the user is cnnected thrugh the best available access technlgy and is able t seamlessly mve between these netwrk technlgies while maintaining cnnectins t applicatin servers, functins are ften cnsidered t be brken int distinct blcks [1]. These include access discvery, access selectin, authenticatin/authrizatin/accunting supprt and mbility management amng thers, as illustrated in Figure 3, based n an apprach presented in [1].

3 Mbility management AAA supprt Access selectin Access discvery Figure 3. Technical cmpnents in an envirnment f multiple access technlgies, as presented in [1]. Access discvery invlves finding the available access netwrks and peridically perfrming new access discvery t find ut if a better alternative has becme available. An imprtant issue invlving these tasks is the cllectin f statistics f the different access netwrks. Access selectin, as its name implies, invlves the prcess f deciding ver which access technlgy the terminal shuld cnnect. In the case f terminal-based access selectin the terminal needs t be infrmed f the capabilities f the access netwrks. In the case f netwrk-based supprt fr access selectin, a netwrk management system is required in rder t prvide netwrk-specific infrmatin and t achieve ladbalancing and t maximize ttal system thrughput. Authenticatin, authrizatin and accunting supprt invlves the tasks f verifying the user s identity, establishing which services the user is entitled t and cllecting all the necessary infrmatin t bill the user fr these services. In a brader sense, the adpted AAA slutin wuld als be respnsible fr the general handling f the user s prfile. The latter is set up when a user subscribes t a service and cntains infrmatin such as the user s persnal preferences, his r her credentials fr authenticatin purpses and accunting data. Mbility management refers t the ability t maintain a sessin when the terminal mves between different access technlgies and t reach the user n his r her current netwrk and terminal at any pint in time. Mbility management may als be enhanced t include the ability t maintain a sessin when the user mves between different devices, in which case apprpriate cntent adaptatin, needed in rder t adapt t different device capabilities, becmes a key issue. The develpment f prtcl slutins fr access discvery and access selectin is a tpic f nging research (e.g. [2]), as n specific standard has yet been develped t cver these tw functins in a systematic way. The Sessin cmpnent f the management architecture discussed in this paper is respnsible fr the executin f these tw functins and fills the abve-mentined gap by adpting a simple signalling prtcl, used between the netwrk management entity and the TSMS, a terminal middleware. This slutin des nt preclude the ptential merging f interfaces, in the future, in a cmmn prtcl that will cver all aspects f the terminal netwrk cmmunicatin. As fr authenticatin, authrizatin and accunting slutins, the Internet Engineering Task Frce is currently develping the standard fr the nextgeneratin AAA prtcl, which is called Diameter. This prtcl prvides a number f enhancements ver the existing prtcl fr remte authenticatin dial-in user service (RADIUS). Where mbility management is cncerned, sessin cntinuity, which refers t the ability t maintain a sessin when the terminal mves between different access technlgies, may be prvided fr thrugh the use f Mbile IP, an IP layer slutin aimed at making mvements n the IP layer transparent t higher prtcl layers. User reachability, which refers t the ability t reach the user n his r her current netwrk and terminal at any pint in time, may be prvided fr thrugh the use f the Sessin Initiatin Prtcl (SIP). Mre specifically, SIP is an applicatin layer cntrl prtcl, whse main functinalities are user lcatin, user availability, user capabilities, applicatin level sessin set-up and applicatin level sessin management [2] TSMS Sessin infrmatin flw The TSMS Sessin cmmunicatin is f paramunt imprtance fr the verall functinality f the cmpsite radi system. It enables the realizatin f the ABC cncept by prviding the infrmatin that is essential fr the executin f the access discvery and access selectin functins discussed in the previus subsectin. The present subsectin gives an verview f the TSMS Sessin infrmatin flw. The prtcl thrugh which the TSMS and the Sessin will cmmunicate must perfrm the fllwing functins: Upn initializatin, the TSMS shall use it t request infrmatin regarding the services that the user f the terminal has subscribed t. The Sessin shall in turn use the prtcl t issue a reply t this request. The TSMS shall use it t request a service. The Sessin shall in turn use the prtcl t accept r t deny this request, and t specify the netwrk t which the TSMS shuld switch fr the prvisin f this service, in case the crrespnding request has been accepted. This functin cnstitutes ne f the mst basic aspects f the cmmunicatin between the TSMS and the Sessin. The TSMS shall use the prtcl t ntify the Sessin that a service has stpped running n a terminal, and the Sessin may use it t explicitly ask the TSMS t stp a service. The TSMS shall use the prtcl t peridically reprt t the Sessin the list f available netwrks in the terminal and the list f services that the terminal is running. The TSMS shall als

4 reprt t the Sessin a set f status parameters f the terminal and f each f the available netwrks in the infrastructure (fr example bit rate, received pwer level, etc.). The prtcl shuld supprt the transmissin f these quality reprts bth n the TSMS s wn initiative (fr instance when the perceived service quality is reduced) and upn a request frm the Sessin. The TSMS shall use the prtcl t issue keepalive prbes, s that the Sessin can be aware f an unexpected terminatin f the terminal, that wuld therwise g unnticed. This infrmatin is critical t the Sessin since the validity f its calculatins relies heavily n the accuracy f the infrmatin it receives regarding the number f terminals that are present in the netwrk and the services that are assciated with these terminals. The Sessin shall use the prtcl t instruct the TSMS t perfrm a vertical handver t a different netwrk. In emergency situatins, such as verall netwrk degradatin, the prtcl may als be used t request quality parameters frm the terminal. In such a case, the TSMS shall in turn use the prtcl t prvide the Sessin with the requested measurements reflecting the quality level at which each service is prvided t the particular terminal Sessin cre peratin The Sessin is the NSMS mdule respnsible fr perfrming all peratins cncerning the cmmunicatin between the NSMS and the terminal. It cmpses, sends, receives and prcesses the messages thrugh which this cmmunicatin is achieved, accrding t the adpted cmmunicatin prtcl. The Sessin hlds infrmatin abut the active terminals that are served by each netwrk, and als abut the quality level assigned t them. Based n that infrmatin and n cnsequent calculatins, it issues recmmendatins t the terminals n chsing the best available netwrk fr the prvisin f a particular service. Thus, the Sessin addresses a shrt-term ptimisatin prblem, targeted t the assignment f the user terminal t a specific netwrk. The slutin f this ptimisatin prblem enables the sphisticated selectin f the apprpriate radi technlgy, fr a specific user, thrugh which services can be btained efficiently in terms f cst and QS, in near real time. The ptimisatin prblem addressed by the Sessin relies n the fllwing input data: (a) the set f services the user is requesting and the crrespnding set f quality levels at which these services are requested; (b) the prfile f the user requesting the set f services. This includes parameters such as the maximum price that the user is willing t pay fr the requested services; (c) the netwrk plicies. This mainly invlves the cst deriving frm the assignment f the user demand t the several quality levels. The ptimisatin prcess carried ut by the Sessin shuld result in an allcatin f the requested services t specific quality levels, and in an allcatin f the requested services t specific netwrks. The calculatin f these allcatins shuld ptimise an bjective functin, which is assciated with the quality levels at which each service will be prvided, and the utility deriving frm the assignment f the user demand t high quality levels. These allcatins are bund t certain cnstraints, such as the capabilities f the user terminal, r the limit t the verall price that the user is willing t pay during usage f the cmpsite radi system. The Sessin ptimizatin prcess is illustrated in Figure 4. Service Request User Prfile Netwrk Plicies Optimizatin Prcess Allcatin f services t netwrks Allcatin f services t quality levels Figure 4. Sessin ptimizatin prcess 4.4. Sftware aspects As previusly stated, the TSMS NSMS cmmunicatin cnstitutes a cardinal part f the verall system management prcess. An interesting issue invlves the sftware aspects regarding the afrementined cmmunicatin. This subsectin presents a first apprach regarding this issue. The selected prtcl fr the cmmunicatin between the TSMS and the Sessin f the NSMS must be able t carry ut all the functins utlined in subsectin B in a simple way. This means that it shuld perfrm the tasks f requesting, allwing, denying and stpping a service, the task f requesting and issuing infrmatin regarding the terminal s quality parameters r the services a user is subscribed t and, finally, the task f instructing a terminal t perfrm vertical handver using as few messages as pssible and aviding redundancy in the exchanged infrmatin. It als means that the prtcl shuld be able t carry all the necessary types f data structures, encde IP addresses, netwrk lists and netwrk types and, ideally, intrduce as little verhead as pssible. It can be viewed as a signalling prtcl, since data transprted in its messages is nt applicatin data. Thus, it shuld use as few resurces as pssible, since resurces shuld be available fr the user. Anther imprtant requirement invlves the speed with which this signalling infrmatin is relayed acrss the netwrk: sme f the messages that need t be exchanged can be urgent, like the ntificatin f netwrk unavailability, r the request f a netwrk switch. It is imprtant t nte that typical rund trip times in GPRS cnnectins can be f abut half a secnd, s the number f required packet exchanges in rder t send a message thrugh the TSMS Sessin prtcl must be as small as pssible. The selected prtcl shuld als prvide a mechanism fr the authenticatin f the exchanged

5 messages. Authenticatin is used t prve the identity f the sender and t guarantee that the message has nt been mdified in transit. It shuld als supprt antireplay prtectin. This is imprtant fr tw reasns: First, frm the security pint f view, an eavesdrpper culd intercept a message and send it again withut mdifying it, thus causing cnfusin in the system. Secnd, it is als pssible fr the netwrk t duplicate packets because f retransmissins. The prtcl must als supprt acknwledgements fr sme messages, t guarantee that they arrive. Nte, hwever, that nt all types f messages may require acknwledgements. Finally, it must prvide a slutin fr cmmunicatin when ne f the cmmunicating entities is behind a NAT gateway. Anther imprtant pint is the fact that the TSMS Sessin interactin can easily be viewed as a client - server mdel, with the TSMS acting as the client and issuing requests and reprts, and the Sessin acting as the server, issuing replies and ntificatins. This bservatin, cmbined with the abve-mentined requirements, culd lead t the decisin t define this prtcl ver UDP, as presented in [4]. UDP ffers a way f sending encapsulated IP datagrams withut having t establish a cnnectin between the parties exchanging the infrmatin. In general, UDP is characterized by speed and simplicity, its mst significant dwnside being the lack f reliability where retransmissin and rdering f packets are cncerned. TCP, n the ther hand, effectively deals with bth f these issues at the cst f speed. In additin, many client - server applicatins, which invlve requests frm the client and subsequent replies frm the server, prefer using UDP, rather than anther transprt layer prtcl, fr example TCP, that wuld have t g thrugh the truble f establishing and releasing a cnnectin. It shuld be nted hwever that the adpted prtcl fr the TSMS Sessin interactin culd just as well be defined ver TCP, r ver a higher-level prtcl. In any case, the underlying philsphy shuld be the same. As mentined in subsectin B, the TSMS Sessin interface is als used t reprt t the latter a set f status parameters f the terminal and f each netwrk. The status parameters that are netwrkspecific refer t the physical layer (fr instance the received pwer level) and the data link layer (fr instance bit rate) f the different radi segments, as well as t the netwrk / IP layer (fr instance upstream / dwnstream IP layer bit rate). In this sense, this interface ffers a means fr perfrming a netwrk mnitring task, much like the SNMP prtcl des: SNMP ffers a systematic way f mnitring and managing a netwrk. Managed ndes in the netwrk must be able t lcally run a managing prcess, an SNMP agent, that will keep a lcal data base f variables describing its status and histry. The ttal f all variables (bjects) in the netwrk is given in the Management Infrmatin Base (MIB). The managing statin interacts with SNMP agents thrugh the SNMP prtcl, which allws the managing statin t ask abut the status f an agent s lcal bjects and t change them if necessary. The SNMP mdel assumes that every managed nde is able t internally run an SNMP agent. This hwever may nt be true f sme devices. In general, althugh SNMP ffers a wide range f netwrk mnitring and managing capabilities, prviding a large amunt f infrmatin frm all layers, it is a bulky prtcl that is impractical t implement in the device scale f laptps and prtable phnes. 5. The Netwrk The Netwrk is respnsible fr the mnitring f the managed netwrk infrastructure. Mre specifically it mnitrs and analyses the statistical perfrmance and QS levels prvided by the netwrk elements (segments) f the managed infrastructure, and the assciated requirements riginating frm the service area (envirnment cnditins, e.g., traffic lad, mbility levels, etc.). It als assesses the relevant netwrk and service-level perfrmance, and dynamically finds and impses the apprpriate traffic distributin, thrugh which the service management requests, and service area cnditins are handled in the mst cst-efficient manner. The Netwrk cnsists f the fllwing entities: Resurce Brkerage, Service Management, and Mnitring and Cnfiguratin (Figure 5) ([5],[6]). The general functinality f the Resurce Brkerage sub-cmpnent is t c-rdinate all the ther entities f the NSMS in rder t handle varius cnditins, such as cngestin in a certain service area. The Service Management entity prvides ptimisatin functinality fr determining the apprpriate service cnfiguratin (allcatin t QS levels) and aggregate traffic distributin (allcatin t netwrks). The peratin f these tw sub-cmpnents is independent frm the underlying radi access technlgy. The Mnitring and Cnfiguratin entity n the ther hand, depends n the radi access technlgy. This latter cmpnent prvides auxiliary functinality fr handling new service area cnditins r management requests. It mainly mnitrs the underlying netwrk segments and frwards the related infrmatin t the Resurce Brkerage entity. Service Management Netwrk 6. Results Resurce Brkerage Mnitring and Cnfiguratin Figure 5. Netwrk sub-cmpnents peratin independent f the underlying radi access technlgy peratin dependent n the underlying radi access technlgy A labratry envirnment invlving real netwrk segments and innvative terminals was used fr cnducting a series f experiments validating the Sessin functinality and its interactin with

6 the terminal as well as the peratin f the NSMS in general. The labratry cmpsite netwrk infrastructure, cmprises GPRS, Wireless Lcal Area Netwrk (WLAN) and Digital Vide Bradcasting Terrestrial (DVB-T). The GPRS netwrk cnsists f a GPRS cell with 8 time slts (TS) available fr GPRS usage with CS-2 mdulatin type. A WLAN IEEE b Access Pint als cvers the area. The DVB-T netwrk cnsists f a DVB-T gateway, in charge f multiplexing the packet traffic frm an Ethernet interface int the DVB-T signal, a DVB-T mdulatr and a RF cnverter. The utput rate fr IP services was set at 10Mbps thrugh prper cnfiguratin f the DVB-T gateway. A MIPv4 platfrm with a GPRS NAT handling mdule ffered t the terminals seamless handver supprt between the varius netwrk segments. Three types f services have been assumed, namely Vide Streaming, Sprts Event and Generic Internet Service Prvisin (e.g. Web brwsing). Figure 6 prvides the tw reference quality levels per service Sprts event Vide streaming Generic Internet Figure 6. Quality f Service reference levels High quality user bit rate Lw quality user bit rate In the results presented here, the initiatin f the test case scenaris is made thrugh the GPRS netwrk. In ther wrds, the GPRS netwrk is cnsidered the Hme netwrk. Hwever, the results btained can be cnsidered generic with respect t which underlying wireless access technlgy is cnsidered the Hme netwrk. Figure 7 depicts a snapsht f part f the graphical user interface f the TSMS cntacting the Sessin in rder t request a Generic Internet Service. The Sessin indicates the apprpriate netwrk (GPRS) and quality level (high) which results in the TSMS remaining at the GPRS netwrk and starting the service. Sessin Figure 7. Result f Generic Internet Service Request In the sequel (Figure 8), the TSMS requests a mre demanding service, i.e. Vide Streaming service. The Sessin addresses the shrt-term ptimisatin prblem discussed earlier and instructs the terminal t switch t the WLAN netwrk in rder t btain bth services at the highest pssible quality level. Sessin Figure 8. Result f additinal request fr Vide Streaming service The results depicted abve are btained when the status f the GPRS and WLAN netwrks is such that allws the efficient, in terms f QS, prvisin f services. Alternatively, a situatin may ccur where fr example, althugh the terminal requests a lw demanding service (e.g. Web brwsing), the GPRS Netwrk is nt available. This will result in the Sessin addressing the shrt-term ptimisatin prblem, taking int accunt that the available netwrks are nw nly WLAN and DVB. It shuld be nted that fr the test case discussed here, the Sessin, thrugh netwrk cst parameter set up, was cnfigured t cnsider the WLAN netwrk as the lwer cst netwrk (cmpared t DVB). Therefre, in a case where GPRS is unavailable, as the ne described abve, and the user requests Generic Internet, the terminal is instructed t switch t the WLAN netwrk, as illustrated in Figure 9. Sessin Figure 9. Result f Generic Internet Service Request The results intrduced in this subsectin are indicative f the functinality f the Sessin and its interactin with the terminal. 7. Cnclusins This paper presented a management architecture that enables wireless systems t perate in the Beynd 3G cntext, while allwing users t benefit frm the Always Best Cnnected cncept. It described the structure and functinality f a netwrk and service management system (NSMS) fr hetergeneus wireless access netwrks, capable f ptimising service delivery and traffic lad distributin in cmpsite radi envirnments. It elabrated n the cre functinality f each f the NSMS s main mdules, namely the Sessin and the Netwrk, and gave special

7 fcus n issues regarding the cmmunicatin between the user terminal and the Sessin. A test case where the validity f this management architecture s, and especially the Sessin s, functinality is verified, and cnsequent results, were presented. REFERENCES [1] E. Gustafssn and A. Jnssn, "Always Best Cnnected", IEEE Wireless Cmmunicatins, February [2] E. Njedju, P. Bertin, P. Reynlds, "Mtivatin fr Netwrk Cntrlled Handffs using IP Mbility between hetergeneus Wireless Access Netwrks", IETF Internet Draft, draft-njedjuinter-an-handffs-00.txt, June 2003, wrk in prgress. [3] J. Rsenberg, H. Schulzrinne, G. Camarill, A. Jhnstn, J. Petersn, R. Sparks, M. Handley, E. Schler, "SIP: Sessin Initiatin Prtcl", RFC 3261, June [4] M. Catalina Galleg, P. Rux, "Candidate Netwrk Selectin in Cmpsite Radi Envirnments", accepted fr publicatin in HET- NETs 03 Technical Prceedings, July [5] G. Kundurakis, N. Kutsuris, V. Stavrulaki, L. Papadpulu, V. Tuntpuls, D. Kuis, P. Demestichas, N. Mitru, "Netwrk and Service Management System fr Optimising Service Delivery and Traffic Distributin in Cmpsite Radi Envirnments" In Prc. IST Mbile &Wireless Telecmmunicatins Summit 2003, Aveir, Prtugal, June [6] P. Demestichas, N. Kutsuris, G. Kundurakis, K. Tsagkaris, A. Oiknmu, V. Stavrulaki, L. Papadpulu, M. Thelgu, G. Vivier, K. El Khazen, "Management f Netwrks and Services in a Cmpsite Radi Cntext", IEEE Wireless Cmmunicatins Magazine, August 2003 (Evlutin twards 4G Mbile Cmmunicatin Systems).