TS 23.417 (SA2) TISPAN – IP Multimedia Subsystem (IMS) – Functional architecture. Full Table of Contents for TS 23.417 PDF version: 7.0.0. 3: IMS VoLTE Architecture & Specs This is 3GPP IMS Architecture, I am going to simplify this moving ahead & you will be able to understand every individual component This VoLTE IMS Architecture is covered under @ 3GPP 23.228.
Youtube Views: 5,883 What is VoLTE? As diagram suggest, it’s all about carrying voice over LTE Data Network Since IMS is part of the Third Generation Partnership Project also called as 3GPP, this makes IMS as Standard solution with Pre-Defined Interworking with underlying 3G & 4G Services.
Flexibility and expandability would allow Operators to bring new services on-line as those services emerge and evolve. IMS is designed to offer unprecedented convenience for individual and business users. Along with LTE Network, Operators can harness the true power of IMS which stands for IP Multimedia Subsystem. IMS is a standalone system which resides out of the LTE network and connected to PDN Gateway or PGW through SGi interface The idea of IMS is very old & was very popular around Year 2004, this used to be a failed Concept prior to support of VoLTE Services. In that Era, Originally the concept for an SMS and voice system over LTE using IMS had been opposed by many operators because of the complexity of IMS.
They had seen it as far too expensive and burdensome to introduce and maintain. With VoLTE Launch, This again got popular and in Demand now a days with LTE & VoLTE Services VoLTE Building blocks Rather than the 2G or 3G connections which are usually used for voice calls, VoLTE offers voice calls over all IP to IP based 4G Network. We tend to think of 4G as mostly being about downloading, streaming and web browsing, and indeed that’s primarily what it’s been used for so far, but it can also be used to next Level of Voice Services with IMS Benefits of VoLTE for End Users. Fast Call Setup – VoLTE can connect calls up to twice as fast as the currently used 2G and 3G Networks. Typical 2G / 3G Call takes 4-6 Seconds while VoLTE Calls requires only 2 Seconds. Superior call Experience – The Greatest advantage of VoLTE is that Voice call quality is superior to 3G or 2G connections.
Essentially it’s an HD voice call and it’s a much richer experience over all. This also offers Improved connectivity.
Video calling– It’s also theoretically possible to make video calls over 4G, much like a Skype call except you’d just use your mobile number and be able to use the regular dialer and call interface, so you can make and receive video calls from anyone else with VoLTE, rather than relying on separate accounts. Better battery life – Anyone who currently uses 4G could also find their battery life increased with VoLTE.
For a Non-VoLTE call, Handset needs to switch from 4G to underlying 3G or 2G network to receive voice call. This is done using CSFB or Circuit Switch Fall Back technology. This frequent switching of Mobile from 4G to 3G & Vice versa consumes lots of Battery. In VoLTE call, Users Need not to Go to 2G or 3G Network to receive voice call VoLTE Network – Building blocks Here, We are going to further Deconstruct End to End VoLTE Network from User Device to IMS Core. SIP Enabled User Equipment:- This Handset or Smartphone needs to be VoLTE Compliant where SIM should support ISIM & SIP User Agent for making VoLTE Calls based on SIP Technology.
VoLTE Call requires adaptability from both Handset & Underlying LTE network. The 4G or LTE Network also needs to adapt with minor tweaks to support VoLTE. IMS Network is sitting on top of underlying LTE Network. Here IMS Core will be interfacing with Traditional LTE Network Nodes such PGW, PCRF & HSS.
In last on Right hand corner, We are having PTSN Network consisting of MSS, MSC & MGW 1: VoLTE Handset Components (User Equipment) For VoLTE to work, User handset must support two critical things: a) SIM Support and b) VoLTE Binary Application in Handset also called as User Agent Evolution of SIM Cards SIM also plays crucial role in VoLTE Support, Technical name of SIM is Universal Integrated Circuit (UICC). There are primarily 3 types of SIM Cards:-. Subscriber Identity Module (SIM): Traditional SIM. This an integrated circuit that securely stores the international mobile subscriber identity (IMSI) and the related key used to identify and authenticate subscribers on mobile telephony.
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UMTS Subscriber Identity Module (USIM): New Age SIM came to support USIM & LTE Networks. IP Multimedia Services Identity Module (ISIM): ISIM identity information used by the VoLTE or IMS subsystem VoLTE SIM. IP Multimedia Private Identity (IMPI): IMPI is a global identity allocated by home network. IMPI contains home operator’s domain information. IP Multimedia Public Identity (IMPU): IMPU acts like a telephone number which can either be a SIP URI (sip:@:) or a tel URI as defined in RFC 39664 ( tel: ) Unlike, 2G or 3G or LTE, Where all Handsets are default supporting all available Network, VoLTE requires detailed Handset testing and Certification for Every Handset Make & Model. This testing is required as handset manufacturers and operators will be seeking to assure themselves that the underlying protocol features are present and functioning correctly. Operator want to ensure that the underlying IMS and protocol is functioning, and performing as intended, in order to deliver the expected quality of service VoLTE Handset VoLTE Handset hosts Binary Application containing SIP User Agent (SIP-UA).
This resides in the User equipment to transmit & receive SIP messages. It Provides basic telephony functionality & can act in two different roles:-. User Agent Server (UAS): Acting as Server to receive requests and send response. User Agent Client (UAC): Acting as Client to send SIP request 2: LTE Architecture I assume you already know LTE Architecture & will not spend too much time here.
All Yellow Nodes are control Plane & are responsible for User Authentication. Control plane nodes include EnodeB, MME, HSS, OCS & PCRF The Green ones are User Plane which includes EnodeB, SGW & PGW.
EnodeB is Radio cell site of LTE Network & is used in both Control & User Plane. PGW is also used for both User & Control Plane traffic Now, We have covered User Handset & LTE Core Network. Its time to demystify IMS Core network. VoLTE Voice Call Traffic is originated by User Handset & Terminates on IMS Network. LTE Network is just used as Bridge acting as IP Supporting Carrier for this communication 3: IMS VoLTE Architecture & Specs This is 3GPP IMS Architecture, I am going to simplify this moving ahead & you will be able to understand every individual component This VoLTE IMS Architecture is covered under @ 3GPP 23.228.
You can also study GSMA Document: GSMA FCM.01 and GSMA IR.92 for further reading LTE to VoLTE Journey, Here is IMS We will start with High level concept of LTE Network & Stitch it together with IMS. This is typical LTE Network which Provides high Speed Internet access. Traffic flows all the way from Mobile handset to EnodeB to SGW to PGW to Internet Cloud Signaling is controlled by MME and PGW with support of HSS, PCRF. LTE Network is part of Evolved Packet System as shown in diagram here.
IMS Core is directly connected to PGW as shown on screen. This is connected over sGi Interface. For LTE Network, IMS or SIP traffic is just another Payload similar to Internet Traffic. LTE PGW doesn’t Decode or Interfere this traffic.
LTE is used as Carrier for accessing IMS Services which provides IP Telephony or Voice Services over IP Network, There could be multiple Access type for IMS Network such as Wifi, or Fix Broadband SIP Server From here onwards, I will start breaking down IMS Cloud in various Bits & Pieces to make it more clear to understand. IMS Core consists of broadly Two Type of Network Elements, First is SIP Infrastructure & Another type of Nodes are Media Gateways. These are tightly coupled under IMS Core Network. Function of SIP Server.
Users are going to register with SIP Server which is Part of Control Plane & Signaling. This SIP Server will setup Media Part or Payload of Voice Call with Media Gateway shown in in Blue Color which is further connected to PSTN. SIP Server is anchoring point for Session set-up, session tear-down, session control and CDR Generation Media Gateway Role of Media Gateway ( Highlighted in Green Color in above figure ). Media Gateway is Responsible for carrying actual voice traffic & handing it over to other Networks. These Media Gateways handles interworking of Voice traffic between IMS & PSTN Networks. Any call coming from traditional 2G or 3G or Fix line network is using this Media Gateway as Entry point to IMS Network.
Media Gateway is Interconnect point to circuit-switched networks and Other IMS Network. It also handles Transcoding of the media plane Role of IPCAN For the sake of easiness, I am using only One Box depicting LTE Network consisting of MME, SGW & PGW.
There can be multiple access networks for providing IMS Services such as Wifi, Fix Broadband, DSL & LTE Networks. As long as user handset supports SIP Device & has IP connectivity to reach IMS Network, We can offer IMS Services to User IPCAN Stands for IP Connectivity Access Network.
This is equivalent to Bearer to IP Connectivity established from user towards IMS or Service Network The SIP Proxy Now, I am going to discuss most critical Element of IMSI Core Network. We call this as CSCF, It stands for Call Session Control Function & act as heart of the IMS system. The CSCF performs all the signaling operations, manages SIP sessions and coordinates with other network entities for session control, service control and resource allocation. It consists of three different entities: the Proxy-CSCF (P-CSCF), the Interrogating-CSCF (I-CSCF) and the Serving-CSCF (S-CSCF).