Virtualization of VoIP Application Servers for Implementation of Private Unified Communication Services via LTE

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1 18. VDE/ITG Fachtagung Mobilkommunikation May Osnabrück, Germany Virtualization of VoIP Application Servers for Implementation of Private Unified Communication Services via LTE Claas Felix Beyersdorf, Diederich Wermser, Daniel Hartmann (Ostfalia University of Applied Sciences, Research Group IP-based Communication Systems, Salzdahlumer Str. 46/48, D Wolfenbüttel). Xing Cao (IANT Applied NGN Technologies GmbH). Contact: [email protected] Abstract Today s LTE networks with their Evolved Packet Core architecture (EPC) provide an excellent platform for transparent integration of mobile User Agents (UA) into corporate VoIP and Unified Communication (UC) environments. Voice over LTE (VoLTE) can either be controlled by IP-Multimedia Subsystem (IMS) run by mobile network operators or by external Application Servers (AS) run by other parties. This paper introduces first approaches and research goals of an R&D project focussing on solutions for implementation of corporate VoIP and UC services by external Application Servers. Virtualization of Application Servers for real-time communication services is a particular focus of the considerations. 1 Introduction Large organisations like companies intend to have private communication networks or services, which seamlessly include all employees, wherever they geographically are and whatever communication device they just use. Beyond store-and-forward services like this is also expected for Real-Time- Communication (RTC) like voice or video services. As long as only circuit switched mobile networks like GSM could meet the requirements of RTC, Closed User Group services were offered by respective mobile network operators. However, these services only offer a set of standard features limited by supplementary services or IN-features run by the operator. LTE with EPC as core-network for the first time enables RTC over IP in mobile WANs and thus the possibility to have full feature-transparency for corporate UC Services to roaming mobile devices. 2 Seamless Integration of Mobile Users to Company RTC 2.1 Traditional FMC becomes obsolete The traditional solution to achieve integration of mobile users into company RTC services when using circuit switched mobile networks like GSM are known as Fixed Mobile Convergence (FMC) [2]. For a caller the current whereabouts of an FMC client and its mobile number of the appropriate public mobile network is not visible. Figure 2 illustrates the handling of a mobile originated call (MO) in FMC, when only circuit switched connectivity is provided by the mobile network. Figure 3 shows the handling of an MO call applicable, when the mobile network offers non-rtc capable IPconnectivity like GPRS in parallel to circuit switched RTC. In both scenarios the FMC controller inside the corporate network establishes the required connections.

2 Figure 1: LTE / EPC with IMS and Private Application Server Controlling QoS Parameters (Simplified) Scenario 1 does not allow for featuree transparency, the FMC user is limited to the CS feature set offered by his public mobile network operator. In contrast inn sce- with IT-applications of the respective company can be nario 2 advanced presence services or CTI-integration provided, as the entiree signalling for call control with the companies RTC server is done over IP. 2.2 RTC services based on EPC/LTE Figure 1 gives a simplified view on LTE/ /EPC with network elementss being particularly relevantt for RTC. Different from previous mobilee network technologies EPC/LTE works All-IP, i.e. also RTC services are based on IP. VoIP P in LTE is frequently called VoLTE [19]. Quality of Servicee (QoS) parameters as welll as Multi- (emlpp) can be controlled through the Policy and level Precedence and Pre-emption Mechanisms Charging Rules Function F (PCRF) either by an a IMS of the network operator or through the Rx Interface using the Diameter-Protocol byy external Application Servers. Figure 2: Pure CS based FMC Solution Table 1 lists the QoS classes as defined in 3GPP TS [7], the emlpp e mechanisms are defined in 3GPP TS [10]. Table 1: QoS Class Identifierss [7] Figure 3: FMC Solution with CS RTC and non RTC-capable IP Connectivity in Mobile Network

3 Figure 4: SipXecs [3]as an SSOA Example, modified from [1] A company aiming at seamless integration of mobile users into its internal RTC services can either inter- the connect these servicess with the ones offered byy LTE operator based on his IMS using an appropriate Session Boarder Controller (SBC)) or use the LTE /EPC as transparent mobile IP-Network throughh SGi Interface with the option to control QoS parameters using the Rx reference point. Seen from the viewpoint of featuree transparencyy for the internal RTC services, the latter alternativee has obvious advantages. On the other hand requirements for high availability of mobile RTC services noww are to be fulfilled by the company s RTC servers. 2.3 Private AS for RTC Services Internal RTC Services, replacing traditional on-site PBX systems, are more and moree offered as cloud services by specialized providers. These providers have to run RTC services for many customers on their server infrastructure and are faced to high requirements with respect to availability. There are two basic architecture alternatives a too implement such a scenario: One Multi-tenant implementation. In I a multicustomers tenancy environment, multiple share thee same application software. Virtualization with (optionally) an individual application software for each customer. As far as knownn by the authors, IMS implements closed user groups for corporate customers by multi- vir- tenancy. However, for private AS to provide RTC Services tualisation has a number of advantages. Application software not developed for multi-tenancy can c be uti- for customer individual servicee features can easily be lized and moreover additionall software components integrated. Major requirements for RTC server solutions in this context are scalability as well as redundancy of main components in order to achieve high availability and load balancing. Moreover M open standard interfaces like SIP, XMPP and REST to allow functional integralike l CRM tion with common enterprise applications or ERP are needed.

4 3 Aspects of Virtualized RTC Servers Running services like web or l in virtualizedd en- vironments is nothing special nowadays. But expand- ing the spectrum of virtualized services to real-time applications like VoI IP or unified communications (UC) in general requires a careful investigation, which will be discussed in this chapter. When it comes to virtualizing of Vo oip systems, a par- ticular notice has to be taken of media-related pro- uncritical, since SIP has its own timing- t and error- handling [13]. cesses. The signalling on the other hand is relatively Assuming that CPU and RAM resources of a physical server are properly dimensioned, the t hypervisor for the virtual machines (VM) can be easily configured to provide the appropriate CPU and RAM resources for high priority VMs at any time. I/O activities are more problematic (Figure 5). A me- has to dia related VoIP process p of an SSOA normally transfer 50 packets per secondd of RTP dataa for each direction. At best, those packets should be sent in an isochronous interval; the network interface controller (NIC) has to be exactly e triggered at each 20ms withswitch on out any jitter. Since the NIC acts as a virtual a virtualized machine, an outgoing RTP stream can suffer from high jitter, if other VMs heavily access the same NIC simultaneously. Using several NICs along with pass-throughh mechanismss can ease this problem by allowing a high priority VMM to access one specific NIC exclusively. Aside the presence information, the call-states and the audio data for Interactive Voi ice Response (IVR) or Music on Hold (MoH),( the actual registrations and call detail recordss (CDR) get stored on the hard disc drives (HDD) off the physicall server, as well. With HDDs having the slowest access times in a whole sys- like the tem, it has to bee examined, if UC services Presence Service, IVR or MoHH get affected in i a heavy load scenario caused by lots of f VMs with disc access. With further notice on high availability, the HA of the public operator s architecture now has to be imple- modular mented by the private SSOA s s operator. The structure of an SSOA allows easy distribution of the respective and optionally redundant processes across the physical hardware of a virtualized environment. To meet the demanded HA, noo redundant UC compo- the very nents (i.e. databases) must be distributed onto same physical hardware. Furthermore, it hass to be in- serves vestigated, if the potentially higher granularity or limits the intended scalability and overall perforprocesses, mance, in particular the synchronization which cause additional networkk traffic. Other planned examinations: Figure 5: I/O is Critical for RTC Services An SSOA in parallel to other non-critical services like CRM or web on the same phys- on the ical host. More than one SSOAA competing same physical host. Distribution of several virtualized SSOA across a wide range off physical hosts.

5 4 Clients for Private Mobile RTC Services Many companies aim for desktop virtualization, which is one way to cope with the challenges of BYOD (Bring Your Own Device), as a asked for by to- day s employees. Usability of softphones in the con- text of desktop-virtualization needs additional consid- for mobile RTC services, desktop virtualization seems not to make sense. eration. For smart phones as dominant client devices However, WebRTC [12] as extension for HTML5 offers an excellent portable thin clientt solution for RTC services on smart phones to interactt with private RTC Application Servers based on QoS-controlled trans- parent IP-transport in LTE/EPC mobile networks.. IMS vendors like Ericsson have already announced to support WebRTC clients for IMS-based real-timee ser- and media for a simple two-party call, when using SSOA (Figure 6) respectively a Back-to-Back-User- Agent architecture for the RTC AS (Figure( vices [20]. Figure 6 and Figure 7 illustrate routes of signalling 7). 5 Outlook This paper considers a varietyy of aspects relevant r to enable seamless access a to corporate RTC services for mobile users, based on LTE/EPC mobile networks. Further research activities a will l focus on virtualization of RTC Application Servers and in particular implementation of tests, that proof keeping of QoS paramesituations ters for media services under extreme load in the virtualization environment. As long as LTE radio networkss have insufficient covbe applied. erage, Voice Call Continuity (VCC) has to It enables seamless handovers s between VoLTE (con- switched trolled by an IMS) and GSM-based outside the LTE coveragee [11]. Po- circuitt voice transmissionn tential solutions offering o an equivalent extension be- when yond the LTE coverage need to be addressed external corporate RTC application servers will be used. Traditional FMC solutions as described in chap- Also, usability of WebRTC for mobile RTC Clients on ter 2.1 could perhaps contributee to this aspect. smart phones in interaction i with external RTC appli- cation servers needs more thorough consideration. Figure 6: WebRTC protocol stack with SSOA Figure 7: WebRTC protocol stack with B2BUAA

6 6 References [1] Schumacher, Jan; Wermser, Diederich: VoIP- TK-Anlagen auf Basis von Open Source. Berlin- Offenbach: VDE-Verlag, ntz 7-8, Nov [2] Shneyderman, Alex; Casati, Alessio: Fixed Mobile Convergence. McGraw-Hill, [3] Picher, Michael W.: Building Enterprise Ready Telephony Systems with sipxecs 4.0. Packt Publishing, [4] SIPfoundry open source community. April [5] Hartmann, Daniel; Stephan, Mark; Cao, Xing et al.: Initial Development of a SIP-/RTP-based Core Network for the TETRA Mobile Radio System aiming at Transparent Availability of its Features in LTE. Osnabrück: 16. ITG- Fachtagung Mobilkommunikation, [6] Pankratz, René; Hartmann, Daniel; Wermser, Diederich: Spezielle Anforderungen an Virtualisierungslösungen für Software-basierte VoIP- PBX. Leipzip, HfTL Science Days, [7] 3GPP TS : Policy and charging control architecture. Release V12.0.0, [8] 3GPP TS : Policy and charging control signalling flows and Quality of Service (QoS) parameter mapping. Release V11.6.0, [9] 3GPP TS : Service accessibility. Release V12.0.0, [10] 3GPP TS : enhanced Multi Level Precedence and Pre-emption service (emlpp). Release V11.0.0, [11] 3GPP TS : Voice Call Continuity (VCC) between Circuit Switched (CS) and IP Multimedia Subsystem (IMS). Release V7.5.0, [12] Web Real-Time Communication. April [13] Trick, Ulrich; Weber, Frank: SIP, TCP/IP und Telekommunikationsnetze. 4. Auflage, München: Oldenbourg Verlag, [14] Poikselkä, Mikka et al.: The IMS. West Sussex: John Wiley & Sons Ltd, Reprint of [15] Dahlman, Erik et al.: 3G Evolution. 2nd Edition, Burlington: Academic Press, [16] Lescuyer, Pierre; Lucidarme, Thierry: Evolved packet Systems (EPS). West Sussex: John Wiley & Sons Ltd, [17] Agbinya, Johnson: IP Communications and Services for NGN. Boca Raton: CRC Press, [18] Olsson, Magnus et al.: SAE and the Evolved Packet Core. Burlington: Academic Press, [19] Ericsson White Paper: Voice over LTE. oice-over-lte.pdf, December [20] Gabriel, Caroline: Ericsson pushes WebRTC beyond the phone Abbreviations AS B2BUA BYOD CRM CSCF emlpp EPC ERP FMC GPRS GSM HA HSS IMS IN IP IVR LTE MO MoH NGN NIC PBX PCRF PDN PSTN QoS RAN REST RTC RTCP RTP SAE SBC SIP SPR SRVCC SSOA UA UE UC VM VPN VoIP VoLTE WAN XMPP Application Server Back-to-Back User Agent Bring Your Own Device Customer-Relationship- Management Call Session Control Function enhanced Multi-Level Precedence and Pre-emption Evolved Packet Core Enterprise-Resource-Planning Fixed Mobile Convergence General Packet Radio Service Global System for Mobile Communications High Availability Home Subscriber Server IP Multimedia Subsystem Intelligent Network Internet Protocol Interactive Voice Response Long Term Evolution Mobile Originated Music on Hold Next Generation Network Network Interface Controller Private Branch Exchange Policy and Charging Rules Function Public Data Network Public Switched Telephone Network Quality of Service Radio Access Network Representational State Transfer Realtime Communication Realtime Transport Control Protocol Realtime Transport Protocol System Architecture Evolution Session Border Controller Session Initiation Protocol Subscriber Profile Repository Single Radio Voice Call Continuity SIP Service Orientated Architecture User Agent User Equipment Unified Communication Virtual Machine Virtual Private Network Voice over IP Voice over LTE Wide Area Network Extensible Messaging and Presence Protocol