Applying SDN/OpenFlow in Virtualized LTE to support Distributed Mobility Management (DMM)

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1 Applying SDN/OpenFlow in Virtulized LTE to support Distriuted Moility Mngement (DMM) Mortez Krimzdeh, Luc Vltulin, Georgios Krginnis Deprtment of Computer Science nd the Electricl Engineering, University of Twente, Enschede, The Netherlnds Keywords: Astrct: Virtulized LTE, DMM, IP ddress continuity, OpenFlow switches Distriuted Moility Mngement (DMM) is moility mngement solution, where the moility nchors re distriuted insted of eing centrlized. The use of DMM cn e pplied in cloud-sed (virtulized) Long Term Evolution (LTE) moile network environments to (1) provide session continuity to users cross personl, locl, nd wide re networks without interruption nd (2) support trffic redirection when virtulized LTE entity like virtulized Pcket Dt Network Gtewy (P-GW) running on n virtuliztion pltform is migrted to nother virtuliztion pltform nd the on-going sessions supported y this P-GW need to e mintined. In this pper we rgue tht the enling technology tht cn efficiently e used for supporting DMM in virtulized LTE systems is the Softwre Defined Networking (SDN)/OpenFlow technology. 1. INTRODUCTION Long Term Evolution (LTE) is the fourth genertion (4G) technology which is stndrdized y the 3 rd Genertion Prtnership Project (3GPP), see e.g., (3GPP Relese 10, 2013). It is cple of providing high dt rtes s well s support of high speed moility. In the LTE system two min network prts cn e identified which re clled Evolved UMTS Terrestril Rdio Access Network (e-utran) nd the Evolved Pcket Core (EPC). The e-utran consist of se sttions tht re denoted s Evolved Node-Bs (s). Ech of these s re controlling different cells which provide rdio coverge nd connectivity etween the User Equipment (UE) nd the EPC. The EPC is composed of severl network elements. The min importnt ones re the Serving Gtewy (S-GW), the Pcket Dt Network Gtewy (P-GW) nd the Moility Mngement Entity (MME). The P-GW, tht is the min moility EPC nchor point, connects the EPC to other externl networks. A moility nchor point is minly in chrge of moility relted user dt forwrding. Moreover, the P-GW lso performs vrious functions such s IP ddress/ip prefix lloction or policy control nd chrging. The S-GW supports the trnsport of the user dt etween the UE nd the externl networks. The MME is the control node tht processes the moility mngement signling, (i.e., hndover) etween the UE nd the EPC. Moility mngement provides the mechnisms for mintining ctive nd semless session continuity to users cross personl, locl, nd wide re networks without interruption. Most of the current IP moility solutions stndrdized y oth IETF (Internet Engineering Tsk Force) nd 3GPP rely on centrlized moility nchor entity which is in chrge of oth moility-relted control plne nd user dt forwrding. The presence of this centrlized network node mkes moility mngement prone to severl prolems nd limittions such s: (1) suoptiml routing, (2) low sclility, (3) signling overhed, (4) more complex network deployment, (5) security nd reliility issues due to the existence of potentil single point of filure, nd (6) lck of grnulrity on the moility mngement service, see e.g. (Bertin et l, 2009), (Chn et l, 2011). Currently, opertors nd reserch communities re investigting lterntive moility solutions tht re more distriuted in nture, y using distriuted moility nchors, denoted s Distriuted Moility Mngement (DMM). The use of DMM llows cheper nd more efficient network deployment cple to meet their customer requirements. As shown in Figure 1, DMM implements fltter system in which the moility nchors re plced

2 closer to the user, distriuting the control nd dt infrstructures mong the entities locted t the edge (ccess) of the network. DMM my e prtilly or fully distriuted, where in the former the distriution scheme is pplied only to the dt plne while in the ltter to oth the dt nd control plnes. It is importnt to notice tht in the fully distriuted pproch dt nd control plnes needs to e decoupled lthough they re oth hndled y the distriuted nchor points. Registrtion Route Setup Control Function Route Setup Registrtion Figure 1.Generic DMM pproch scheme The Cloud Networking (MCN) project 0(EU FP7 MCN, 2013), s one of the EU FP7 projects, integrtes the use of cloud computing concepts in LTE moile networks in order to increse LTE s performnce. This is ccomplished y uilding shred distriuted LTE moile network tht cn optimize the utiliztion of virtulized computing, storge nd network resources nd minimize communiction delys. In prticulr, the integrtion of cloud computing concepts in LTE system, cn e relized y: (1) extending the cloud computing concept eyond the typicl (mcro) dt centers towrds new smller (micro) dt centers tht re distriuted within the e- UTRAN nd the EPC, nd (2) deploying nd running cloud-sed (virtulized) e-utran, denoted s RAN s Service (RANS), nd EPC, denoted s EPC s Service (EPCS). This trend is lso in line with the emerging ETSI ctivities in Network Functions Virtuliztion (NFV). The use of DMM cn e pplied in such environments not only to enhnce the LTE moility mngement performnce nd provide session continuity to users cross personl, locl, nd wide re networks without interruption, ut lso to support trffic redirection when virtulized LTE entity, like the P- GW running on n virtuliztion pltform (i.e., originting dt centre) is migrted to nother virtuliztion pltform (i.e., destintion dt centre) nd ongoing sessions supported y this P-GW need to e mintined. In (Chn, 2013), the min IETF requirements for DMM solutions in IPv6 networks deployments re defined s follows: Distriuted deployment: IP ddress moility nd routing solutions provided y DMM must enle distriuted processing for moility mngement so tht trffic does not need to trverse centrlly deployed moility nchors nd therey void non-optiml routes. Trnsprency: DMM solutions must provide trnsprent moility support ove the IP lyer when needed. IPv6 deployment: DMM solutions should trget IPv6 s the primry deployment environment nd should not e tilored specificlly to support IPv4, in prticulr in situtions where privte IPv4 ddresses nd/or NATs (Network Address Trnsltions) re used. Co-existence: The DMM solution must e le to co-exist with existing network deployments nd end hosts. For instnce, depending on the environment in which DMM is deployed, DMM solutions my need to e comptile with other deployed moility protocols or my need to interoperte with network or moile hosts/ routers tht do not support DMM protocols. Security considertions: A DMM solution must not introduce new security risks or mplify existing security risks ginst which the existing security mechnisms/protocols cnnot offer sufficient protection. Flexile multicst distriution: DMM should consider multicsting. So the solutions cn e developed tht, not only to provide IP moility support when it is needed, ut lso to void network inefficiency issues in multicst trffic delivery (e.g., duplicte multicst suscriptions towrds the downstrem tunnel entities). In the context of this pper lso the following dditionl requirements re defined: Dynmicity: The dynmic use of moility support y llowing the split of dt flows long different pths tht my trvel through either the moility nchor or non-nchor nodes, even though no specific route optimiztion support is ville t the correspondent node. This requirement will tckle the lck of fine grnulrity of the centrlized moility mngement pproches. Seprting control nd dt plnes: Keeping the control plne centrlized while distriuting the dt plne is possile solution to minimize the signling overhed etween the moility nchors due to the lck of knowledge tht distriuted nchor point hs of its peers nd their connected UEs. Network-sed: Not urdening the UE with extr signling nd keeping the user unwre of the on-going hndoff procedure within the sme

3 domin re fundmentl spects tht need to e provided y the DMM solutions deployed in LTE networks. Severl DMM solutions hve een proposed in the IETF nd 3GPP contexts. However, it is not yet cler whether these DMM solutions cn e pplied in virtulized LTE network systems. In this pper we rgue tht the est cndidte enling technology tht cn efficiently e used for supporting DMM in virtulized LTE systems is the SDN/OpenFlow technology. In prticulr, this pper nswers the following reserch question: Cn SDN/OpenFlow e used efficiently for DMM support in virtulized LTE systems? This pper is orgnized s follows. Section 2 is providing rief overview of the SDN/OpenFlow technology nd explins how it could e exploited to support DMM in virtulized LTE systems. In Section 3 rief introduction of other possile cndidte technologies is provided. Moreover Section 3 nlyses nd compres these technologies with the SDN/OpenFlow pproch. Section 4 shows in n exmple how the SDN/OpenFlow concept cn e pplied in the virtulized LTE system. Furthermore, Sections 3 nd 4 re nswering the reserch question listed ove. Finlly, Section 5 concludes nd provides recommendtions for future work. 2. SDN/OPENFLOW SDN (ONF, 2103) is n rchitecture tht decouples forwrding functions nd network control, which ecome directly progrmmle. This enles the underlying infrstructure to e strcted for pplictions nd network services. In prticulr, SDN cple switches nd routers cn e configured nd progrmmed using centrlized mngement entity, denoted s SDN controller. Severl SDN sed protocols re eing developed, such s the IETF FORCES (Forwrding nd Control Element Seprtion) nd OpenFlow. OpenFlow (OpenFlow, 2013) is the most commonly used SDN sed protocol which crries signlling messge etween SDN controllers nd the underlying network infrstructure, ringing network pplictions to life. With OpenFlow, the forwrding plne of SDN/OpenFlow cple switch or router cn e ccessed over the network nd reconfigured ccording to the needs of pplictions nd network services. The vst mjority of Ethernet switches nd routers used nowdys contin flow-tles to implement firewll, NAT, QoS (Qulity of Service) nd other functionlities. A flow-tle of SDN/OpenFlow cple switches or routers cn e remotely progrmmed prtitioning the network s trffic into seprted flows. Fetures offered y OpenFlow protocol cn e used to deploy DMM solution offering IP ddress continuity nd trffic redirection in the opertor s trnsport network. This cn e chieved y treting ech trffic pth from the Internet PoPs (point of presence) to the moility nchor points (e.g., P-GWs) s seprted flow. In this wy trffic redirection cn e supported without involving ny IP ddress trnsltion or modifiction, when for exmple virtulized LTE entity, like the P-GW, running on n virtuliztion pltform (i.e., originting dt centre) is migrted to nother virtuliztion pltform (i.e., destintion dt centre) nd ongoing sessions supported y this P-GW need to e mintined. Alterntively SDN/OpenFlow switches contin list of ctions tht cn e pplied on every trnsiting pcket tht elongs to specific flow. Exmple of these ctions re: Drop, Push-Tg, Pop-Tg, Group nd Set-Field. The optionl Set- Field ction is the most interesting for the purpose of this proposl providing to SDN/OpenFlow switches the possiility to modify heders of pckets nd frmes, used y e.g., Ethernet, VLAN, nd IP. Both flow tles nd ction lists re dded, modified or removed y the SDN/OpenFlow Controller which hs dedicted secure connection with ech SDN/OpenFlow switches nd routers. The procedures nd messges used to support nd perform such modifictions re specified in the OpenFlow specifiction document MOTIVATION: WHY SDN/ OPENFLOW SHOULD BE USED FOR DMM SUPPORT IN VIRTUALIZED LTE SYSTEMS This section introduces other possile cndidte DMM enling technologies nd nlyses nd compres them with the SDN/OpenFlow pproch in order to verify whether they cn e pplied for DMM support in virtulised LTE system IETF sed DMM enling technologies The IETF DMM working group chrter ddresses two complementry spects of moility mngement procedures: the distriution of moility nchors

4 towrds more flt network nd the dynmic ctivtion/dectivtion of moility protocol support s n enler to distriuted moility mngement (Chn, 2013). The following DMM solutions re specified within the context of IETF Doule NAT (D-NAT) Doule NAT DMM solution proposed in (Liesch, 2012) dopts the concept of n identifier-loctor split to solve the routing in the trnsport network ove the moility nchors. Forwrding downlink pckets to the moile nodes s current moility nchor cn e chieved using tunnels s lredy done in oth IP nd Proxy IP (PMIP) solutions. To void encpsultion overhed introduced y tunnelling the use of NAT is proposed t oth ends of the opertor's trnsport network. Two new entities, performing ddress trnsltion from identifier ddress to loctor ddress nd vice-vers, need to e introduced in the network. These entities re referred to s Ingress NAT router nd Egress NAT router. Using NAT functionlity is required only in the cse of downlink trffic, where the Ingress NAT router performs trnsltion of the identifier ddress into the loctor ddress nd it forwrds the pckets down into the opertor's trnsport network. The Egress NAT router, on the other hnd, trnsltes the loctor ddress ck to the identifier ddress in order to forwrd the pcket to the moile node. The Egress NAT routers will therefore lwys e plced closer to the southern edge of the opertor's trnsport network thn the Ingress NAT routers Distriuted Moility Anchoring (DMA) P. Seite (Seite et l, 2103) proposed distriuted moility trffic mngement with dynmic user s trffic nchoring in the networks ccess routers (ARs). It relies on flt rchitecture where new entity nmed Moility cple Access Router (MAR) is introduced to provide moility mngement functions. The MAR hs oth moility nchoring nd loction updte functionl cpilities nd cn cts s Home-MAR (H-MAR) or s Visited-MAR (V-MAR) for given moile node. A H-MAR is responsile for the lloction of Home Network Prefix (HNP), used in this solution insted of HoA, to moile node. On the one hnd, when moile node moves wy from the home network, the H-MAR is responsile for trcking the moile node s loction nd forwrding pckets to the V- MAR where the moile node is currently ttched to. On the other hnd V-MAR mnges the moility-relted signlling for moile node tht is ttched to its ccess link. The rchitecture of this solution relies on centrlized dtse storing ongoing moility sessions for the MNs Inter-domin DMM J.C. Zunig et l. in (Bernrdos nd Zunig, 2103) proposed method which ims to ensure session continuity in n inter-domin roming scenrio. It is sed on the prtil distriuted single opertor scenrio tht uses n entity clled Distriuted Gtewy (D-GW) plced t the edge of the network. The D-GW supports two roles: Anchoring D-GW nd Serving D-GW. The control plne relies on centrl entity clled Centrl Moility Dtse (CMD). The inter-domin solution uses centrlized Locl Moility Anchor (LMA), usully locted in the home domin, s top-level nchor to gurntee session continuity when crossing opertor orders. It is ssumed tht the necessry roming greement re in plce in order to support setting up tunnels etween the LMA locted t the home domin of the moile node (MN) nd the visited D-GWs, which in 3GPP EPC scenrio my correspond to the s or Home s (HeNBs) used for femtocells GPP sed solutions IETF sed DMM enling technologies Currently, in the 3GPP EPC rchitecture, the moility mngement solutions mostly rely on centrlized moility nchor entity, i.e., P-GW, which is in chrge of the control of the network entities involved in the moility mngement nd the user dt forwrding. There re however, two solutions specified y 3GPP tht re lredy introducing the concept of DMM into the 3GPP EPC rchitecture, i.e., LIPA nd SIPTO Locl IP Access (LIPA) / Selected IP Trffic Offlod (SIPTO) LIPA nd SIPTO 0 hve een introduced y 3GPP in LTE Relese 10. They enle dt trffic offlod t pproprite points in the Rdio Access Network (RAN) in highly cost-efficient mnner leding to n incresed system sclility nd enhnce the opertors flexiility to cope with the growing moile dt trffic demnded. LIPA llows UE, connected in residentil or corporte deployment vi HeNB, to directly connect to other devices nd services in the locl network, relieving this portion of dt

5 trffic from the moile opertor s core network. LIPA rekout tkes lwys plce t the newly introduced Locl GW entity locted in the locl/home or enterprise femtocell network. SIPTO, on the other hnd, offlods selective IP trffic to the Internet t the locl gtewy (L-GW), similr to LIPA, or ove HeNB such s the HeNB gtewy locted in home nd enterprise networks. When the UE is connected to mcro-cellulr network, SIPTO offlod tkes plce t or ove the RAN. By reking out selected trffic closer to the edge of the network, opertors my void overloding their scrce resources, i.e. P-GWs nd S-GWs, s well s void inefficient routing in the moile ckhul network Anlysis nd Comprison In order to provide DMM support in virtulised LTE systems, the selected DMM enling technology needs to support the DMM requirements listed is Section 1. Tle 1 nlyses nd compres SDN/OpenFlow technology with the other cndidte DMM enling technologies tht were riefly descried in the previous susections, y using the DMM requirements listed in Section 1. Tle 1. Comprison ( Y:Yes, N:No, P: Prtil, N.c:Not considered, N.s:Not specified, C:Considered, O.l:Only locl, without support for IP ddress continuity) Requirements SDN/ OpenFlow D-NAT DMA Interdomin DMM LIPA/ SIPTO Distriuted Y Y Y P O.l deployment Trnsprency Y Y Y Y O.l IPv6 deployment Y Y Y Y Y Co-existence N N P Y P Security N.c N.c N.c N.c C considertions Flexile multicst Y Y N.s N.s N.s distriution Dynmicity Y N Y N N Seprting control nd dt Y Y Y Y Y plnes Network-sed Y Y Y Y Y Bsed on the nlysis nd comprison given in Tle 1, it cn e deduced tht the SDN/OpenFlow sed DMM technology cn stisfy most of the DMM requirements introduced in Section 1. The Co-existence requirement is not stisfied due to the fct tht SDN/OpenFlow requires the introduction of new entities nd fetures, i.e., SDN/OpenFlow Controller nd switches, in the opertor s trnsport network. However, due to the ongoing ctivities in the SDN re, see (ONF, 2103), it cn e ssumed tht opertors will proly introduce nd deploy SDN/OpenFlow Controllers nd switches in their opertor s trnsport networks. Therefore, it cn e deduced tht the SDN/OpenFlow technology is promising cndidte tht cn efficiently e used for DMM support in virtulized LTE systems. 4. EXAMPLE OF INTEGRATING SDN/OPENFLOW IN VIRTUALIZED LTE SYSTEMS In this section, n exmple is provided on how the SDN/OpenFlow enling technology could e pplied in virtulized LTE systems to support DMM. In virtulized LTE system, the s re running on Virtul Mchines (VMs) tht re hosted on one or more micro dt centres. The DMM frmework descried in (Liesch et l, 2013) cn e used for this purpose. In prticulr, 0(Liesch et l, 2013) defines 4 new functionl entities: FE_I: Ingress for DMM indirection (redirection), FE_E: Egress for DMM indirection, FE_IEC: Control to estlish sttes for DMM indirection nd FE_MCTX: Function to trnsfer/estlish context for IP ddress continuity. In Figure 2, it is considered tht: OF1 supports FE_I nd OF4 nd OF3 support FE_E. The FE_IEC nd FE_MCTX re supported y the SDN/OpenFlow Controller (OC), in coopertion with MME. DMM cn e used to provide (1) session continuity to users (UEs) tht re moving from one moility nchor, e.g., to nother moility nchor, nd (2) trffic redirection when virtulized LTE entity, like the P-GW running on n virtuliztion pltform is migrted to nother virtuliztion pltform nd ongoing sessions supported y this P-GW need to e mintined. In this exmple, DMM is used to provide session continuity to users tht re moving from one virtulized to nother virtulized. In such n rchitecture, SDN/OpenFlow switches nd SDN/OpenFlow Controllers my e implemented in VMs nd the functions cn e remotely configured nd upgrded using soft-epc components sed on the end-users requirements.

6 With OpenFlow the forwrding plne of SDN/OpenFlow switch or router cn e ccessed over the network nd modified ccording to the service requirements. As shown in Figure 2, simple OpenFlow network is used s trnsport network ove the EPC. All the routers re OpenFlow cple nd their flow tles re mnged y the sme OC. technology for the support of DMM in the virtulized LTE system will e prototyped nd evluted within the context of the EU FP7 project 0(EU FP7 MCN, 2013). ACKNOWLEDGEMENTS OpenFlow Controller OF4 d c Internet OF1 OF2 OF3 OpenFlow Controller OF4 d c Internet OF1 OF2 OF3 This work is ccomplished in the context of the MCN project. We therefore, would like to cknowledge the Europen Commission, since the MCN project is n EC funded Integrted Project under the 7th RTD Frmework Progrmme, FP7- ICT grnt greement numer Trget Trget Trget Trget REFERENCES Active flow using IP ddress Active flow using IP ddress Hndover () efore hndover () fter hndover Figure 2. OpenFlow pproch to support DMM in virtulized LTE system In this exmple, when UE chnges his EPC moility nchor point, flow tles of ll SDN/OpenFlow switches will e updted y OC to re-route the downlink trffic (i.e., rriving from Internet), from the originl, see Figure 2(), to the new, see Figure 2(). Due to the fct tht no modifictions will e performed on the dt pckets, trffic redirection cn e performed only if ll routers nd switches in the opertor s trnsport network re OpenFlow cple. For uplink trffic (i.e., sent towrds Internet), sttic forwrding pth will e setup when flow is creted. If pth to the specific destintion hosts lredy exists, for instnce in cse of widely visited end-hosts, no chnges will e needed to the setup pths. This sttic pth will e used throughout the whole life of flow in the opertor s trnsport network. 5. CONCLUSIONS AND FUTURE WORK In this pper severl DMM enle technologies hve een nlysed nd compred. In prticulr, this pper rgued nd verified tht the SDN/OpenFlow technology is promising cndidte tht cn efficiently e used for the support of DMM in virtulized LTE systems. In order to further vlidte this sttement, the use of the SDN/OpenFlow 3GPP Relese 10, 2103.Overview of 3GPP Relese 10 V0.1.7, < Bertin, P., Bonjour, S., Bonnin, J., Distriuted or centrlized moility. In Proc. of IEEE Glol Telecommunictions Conference, (GLOBECOM 2009). pp IEEE. Chn, H.A., Yokot, H., Xie, J., Seite, P., Liu, D., Distriuted nd Dynmic Moility Mngement in Internet: Current Approches nd Issues. Journl of Communictions, Vol. 6, Iss, 1, pp Acdemy Pulisher. EU FP7 MCN, (visited in Septemer 2013) < Chn, H. (editor), Decemer Requirements for Distriuted Moility Mngement. IETF Internet drft (work in progress). IETF. ONF, (visited in Decemer 2013) < OpenFlow, The OpenFlow Specifiction.Version 1.3.0, (visited Decemer) < Liesch, M., Per-Host Loctors for Distriuted Moility Mngement. IETF Internet drft (work in progress). IETF. Seite, P., Bertin, P., Lee, J.H., Distriuted Moility Anchoring. IETF Internet drft (work in progress). IETF. Bernrdos, C.J., Zunig, J.C., PMIPv6-sed distriuted nchoring. IETF Internet drft (work in progress). IETF. Liesch, M., Seite, P., Krginnis, G., Distriuted Moility Mngement-Frmework & Anlysis. IETF Internet drft (work in progress). IETF.