Voice over LTE (VoLTE) with IMS

Course outline : IMS (IP Multimedia Subsystems) has been around for some time, and many infrastructure vendors have invested heavily in developing IMS capabilities, solutions and products. But market acceptance has been slower than expected. Now, with LTE (Long Term Evolution) taking shape, the IMS platform has been given a new role and a niche that will carry it a considerable distance into the future. The goal of this course is to present IMS with LTE+ePC=EPS as the broadband access.

The course:
• introduces the requirements that EPS puts on IMS,
• describes the IMS architecture for EPS
• presents the IMS protocols
• shows how roaming in IMS applies when an EPS user is in a visited network
• describes how resources are reserved in the EPS access network when an IMS session is established
• shows how supplementary services of telephony and SMS are supported
• illustrates the different IMS procedures considering an EPS user : registration, session establishment/release, SMS delivery, charging
• Highlights the following IMS services : USSD over IP, SMS over IP.

1. Introduction to EPS (LTE + ePC) and impact of VoLTE on EPS
1.1. EPS architecture
1.2. EPS, VoLTE and HSS
1.2.1. HLR (2G/3G database)
1.2.2. HSS (EPS database)
1.2.3. UPSF (IMS database)
1.3. EPS, VoLTE and PCC
1.3.1. PCC architecture
1.3.2. New PCC interfaces
1.3.2.1. Rx (Policy Control)
1.3.2.2. Ro (Online Charging)
1.3.2.3. Rf (Offlne Charging)
1.4. EPS and QoS for VoLTE
1.4.1. Default bearer for SIP Signaling (IMS APN, SOS APN)
1.4.2. Dedicated bearer for voice (QCI = 1)
1.4.3. Dedicated bearers for videotelephony : one for voice (QCI = 1 and one for video (QCI = 2)
1.4.4. Default bearer for XCAP signalling
1.5. Comparison between VoLTE and CSFB


2. IMS Architecture and entities
2.1. CSCF : P-CSCF, I-CSCF, S-CSCF for the control of IMS multimedia sessions
2.2. IMS-MGW, MGCF, BGCF, T-SGW for the interworking with circuit switched networks (PSTN, GSM)
2.3. IBCF and TrGw for the interworking with other IMS networks
2.4. HSS database, SLF and DRF(DIAMETER routing function) for the management of user mobility of identification of PCRF
2.5. PCRF for policy and charging control
2.6. CDF and OCS for offline and online charging respectively
2.7. AS, MRF and SCIM for service execution, media delivery and service interaction management respectively
2.8. ATCF and ATGw for SR-VCC procedures
2.9. E-CSCF and LRF for emergency sessions

3. National/International IMS/VoLTE interconnection
3.1. Entities for the interconnection
3.1.1. IBCF, TrGW
3.1.2. MGCF, IMS-MGW
3.1.3. BGCF
3.1.4. ENUM
3.2. VoLTE/VoLTE interconnection
3.3. VoLTE/ Fixed IMS interconnection
3.4. VoLTE/ R4 interconnection
3.5. VoLTE / circuit switching interconnection

4. VoLTE Roaming
4.1. VoLTE roaming architecture
4.1.1. S8HR Mode
4.1.2. LBO Mode
4.1.3. Use case for each mode
4.2. Lawful interception with S8HR and LBO modes
4.3. Emergency sessions with S8HR and LBO modes
4.4. Charging with S8HR and LBO modes
4.5. Media processing with S8HR and LBO modes
4.6. Service invocation with S8HR and LBO modes
4.7. Short number processing with S8HR and LBO modes

5. IMS Procedures : Registration/Deregistration
5.1. Registration with EPS access
5.1.1. Registration from the home network
5.1.2. Registration from the visited network
5.1.3. Authentication with ISIM or with USIM
5.1.4. User Profile
5.1.5. Subscription to registration state change
5.2. Deregistration with EPS access
5.2.1. UE-initiated deregistration
5.2.2. Network-based deregistration (e.g., initiated by S-CSCF)
5.2.3. Administrative deregistration (i.e., initiated by HSS)

6. IMS Procedures : Session Control
6.1. Voice session establishment/release with EPS access with and without roaming situations

7. IMS Procedures : Policy Control for resource reservation in EPS (i.e., dedicated bearer)
7.1. Rx Interface between P-CSCF and PCRF
7.1.1. Rx session for IMS registration
7.1.2. Rx session for IMS session control
7.2. Gx Interface between PCRF and PCEF (i.e., PDN GW)
7.3. Corresponding Scenarios

8. IMS Procedures : Bearer Control for media control
8.1. Iq Interface between P-CSCF/IMS-ALG and IMS-AGW
8.2. Ix interface between IBCF and TrGW
8.3. Corresponding Scenario

9. USSI : USSD using IMS
9.1. USSI principles
9.2. USSI Architecture
9.3. SIP Session for USSI
9.4. SDP for USSI
9.5. UE-initiated USSI operation without additional information request
9.6. UE-initiated USSI operation with additional information request
9.7. Network-initiated USSI operation without additional information request
9.8. Network-initiated USSI operation with additional information request

10. SMS over IP with IMS
10.1. SMS over IP architecture
10.1.1. IP-SM-GW AS
10.1.2. HLR
10.1.3. HSS
10.1.4. SMSC
10.2. SMS delivery
10.2.1. SMS architecture in the IMS framework
10.2.2. Message flow of SMS delivery and SMS reception

11. IMS Centralized services (ICS), T-ADS
11.1. SCC AS (Service Centralization and Continuity) for ICS
11.2. IMRN and CSRN concepts for ICS and T-ADS

12. Conclusion