Chapter 2State of the ArtThis chapter contains an overall description of the VoLTE service in the LTENetwork. It contains a characterization of all the elements involved and therefunctionalities. It also present a process illustration of process used to monitorand evaluate the system which will be important for the next chapters how todevelop a method of forecast.2.1 Long Term EvolutionLong Term Evolution, also known as the Fourth Generation (4G) Technology, is aniteration of the Global System for Mobile Communication (GSM) and UniversalMobile Telecommunications System (UMTS).
However, in contrast with previ-ous circuit-switch (CS) model cellular systems, LTE has been design to supportonly packet-switch (PS) services. The Release 10, also known as LTE-A (LTE-Advanced) launched with three fundamental features which are necessary to fulfillthe throughput objectives proposed by the standards of peak data rates 100 Mbpsin downlink and 50 Mbps in uplink:Robust Modulation in Dense Environments – OFDMA (Orthogonal Fre-quency – Division Multiple-Access) is used in down link to increase spec-tral and SC-FDMA (Single Carrier – Frequency Division Multiple Access) in5
Chapter 2.State of the Artuplink due to cost-efficient reasons. The usage of different modulated sig-nals results in high Peak-to-Average-Power Ratio (PAPR), which results inexpensive and complex UE transmitters.Increased Link Capacity – Carrier Aggregation and MIMO (Multi-Input-Multi-Output) (capable of Spatial multiplexing up to 8 layers in downlinkand up to 4 layers uplink) allow for high bit rate and capacity of the networkcomparing with previous technologies.Flat IP – Flat architecture with a backhaul based on IP and the separationof the user plane and control plane creates an scalable system.(figura da arquitectura de rede) (meter aqui o 3gpp de LTE)2.2 Voice over Long Term EvolutionThe VoLTE solution is a standards-compliant implementation of LTE service ar-chitecture. The solution places IMS functional elements at the center of the voicecore network, managing the connectivity between subscribers and the implemen-tation of policy control .The VoLTE solution is scalable and rapidly deployed, offering rich multimediaand voice services, seamless voice continuity across access networks and the re-useof existing business and operational support components.Nokia VoLTE solution builds upon the One Voice initiative, subsequently re-formulated in GSMA Permanent Reference Document (PRD) IR.92 , IR.94 and IR.64 , empowering operators to roll-out rich communications services andcapabilities across both LTE and hybrid networks.(figura de Arquitectura de VoLTE)The main functional nodes of the VoLTE architecture are defined by 3GPPand are described below according to the 3GPP TS 23.002:66
Chapter 2.State of the Art1. VoLTE User EquipmentThe User Equipment (UE) that is used to connect to the Evolved PacketCore (EPC) via the LTE-Uu radio interface. Each UE must contain oneUniversal Integrated Circuit Card (UICC) and session Initiation ProtocolUser Agent (SIP UA).The most used combination of UICCs in a UE is an UMTS Subscriber Iden-tity Module (USIM) and IP Multimedia Services Identity Module (ISIM).Focusing on ISIM which is need to perform registration on IMS core, itcontains according to 3GPP TS 31.103:IP Multimedia Private Identity (IMPI) – It is a global identity allo-cated by the home network. IMPI contains home operators domaininformation.IP Multimedia Public Identity (IMPU) – Similar to a telephone number,it is used by any user for requesting communications to other users. Itcan either be a SIP URI or a tel URI. Definition of tel URI from RFC39664.Secret Key – This long secret key is used for user authentication andSIP registration.2. eNodeBSingle node that interfaces with the UE. It is responsible to establish thePhysical (PHY), Medium Access Control (MAC), Radio Link Control (RLC),and Packet Data Convergence Protocol (PDCP) layers that include the func-tionality of user-plane header-compression and encryption. It also offersRadio Resource Control (RRC) functionality corresponding to the controlplane. It performs many functions including radio resource management,admission control, scheduling, enforcement of negotiated UL QoS, cell infor-mation broadcast, ciphering/deciphering of user and control plane data, andcompression/decompression of DL/UL user plane packet headers.3. Evolved Packet Core7
Chapter 2.State of the Art(a) Mobility Management EntityThe Mobility Management Entity (MME) handles the signaling andcontrol, mobility and idle management manipulating the distributionof paging messages to the eNodeB. This facilitates optimization of thenetworks implemented and allows total flexibility in expanding the ca-pacity. It also manages the access of the UE to the network throughinteraction with the Home Subscriber Server (HSS) in order to authenti-cate users. Provides the function of the control plane to enable seamlessmobility between LTE and 2G/3G mobile networks and also supportslawful interception of signaling.(b) Serving GatewayThe Serving Gateway (S-GW) acts as the termination point betweenthe radio access network and the Core Network. Forwards data packetsto and from the eNodeB and the Packet Data Network Gateway (P-GW) and performs accounting and control of user data. It also servesas a local mobility anchor for handovers between eNodeBs or passagebetween 3GPP networks and informs the user traffic in case of lawfulinterception.(c) Packet Data Network GatewayThe PDN gateway provides the connection between EPC and a numberof external data networks. It is comparable to GGSN in 2G/3G net-works. It serves as point of entry and exit of data traffic from the UEand interface between LTE networks and packet data networks such asthe Internet or fixed and mobile networks based on the Session Initia-tion Protocol (SIP) or Internet Protocol multimedia subsystem (IMS).It also manages the assignment of IP addresses and supports packetfiltering for each user. Also supports charging and serves as a localmobility anchor for handovers between 3GPP access systems and non-3GPP access systems.(d) Home Subscriber Server88
Chapter 2.State of the ArtThe HSS is a network database that holds both static and dynamicdata elements related to subscribers. The HSS provides user profileinformation to the MME and IMS core during UE attach and IMSregistration.(e) Policy Charging and Rules FunctionThe PCRF provides policy control decisions and flow based chargingcontrols. The PCRF determines how a service data flow shall be treatedin the enforcement function (PGW in this case) and ensure that the userplane traffic mapping and treatment is in accordance with the usersprofile.4. IP Multimedia SubsystemIMS is the control infrastructure for supporting next generation IP Multime-dia Services and consists of many separate elements which are listed below.(a) Proxy Call Session Control FunctionThe P-CSCF is the initial point of contact for session signalling forthe IMS-enabled VoLTE UE. The P-CSCF behaves as a SIP proxy byforwarding SIP messages between the UE and the IMS Core Network,maintains the security associations between itself and the VoLTE UE,and incorporates the Application Function aspect of PCC to enablebinding of the IMS session with the bearer for applying dynamic policyand receiving notifications of bearer level events. The P-CSCF may beimplemented in an Access Session Border Controller which may alsoincorporate the IMS-ALG/IMS-AGW.(b) Interrogating Call Session Control FunctionThe I-CSCF is the contact point within an operators network for allconnections destined to a user of that network. On IMS registration, itinterrogates the HSS to determine which suitable S-CSCF to route therequest for registration. For mobile terminating calls, it interrogatesthe HSS to determine which S-CSCF the user is registered on.(c) Serving Call Session Control Function9
Chapter 2.State of the ArtThe S-CSCF provides session set-up, session tear-down, session controland routing functions. It generates records for billing purposes for allsessions under its control, and invokes Application Servers based onIFCs received from the HSS. The S-CSCF acts as SIP registrar forVoLTE UEs that the HSS and I-CSCF assign to it. It queries the HSSfor the applicable subscriber profiles and handles calls involving theseend points once they have been registered.(d) Media Resource FunctionThe MRF is a common media resource function, for use by IMS Appli-cation Servers and I/SCSCFs, to provide media plane processing inde-pendent of application types, e.g. transcoding, multiparty conferencing,network announcements/tones, etc. under the control of IMS Applica-tion Servers (VoLTE AS) as well as basic media processing functionsto CSCFs. The control plane interfaces to MRFs are defined by the3GPP references Mr, Mr, and Cr interfaces (SIP/SDP and XML en-coded media service requests) while the media plane interfaces to MRFsare defined by 3GPP reference Mb for RTP/RTCP transpor