Contents
The EPS and IMS network architecture and procedures for the voice service in VoLTE solution will be presented, on a level allowing understanding and analysing SIP and Diameter traces from a VoLTE environment. The course includes the enhanced SRVCC solution with the ATCF/ATGW deployment. A significant part of the time will be devoted to hands-on exercises with Wireshark-based traces, with focus on the messages and parameters for the VoLTE-specific traffic cases.
Exercises
This is a theoretical training with practical exercises. The exercises are hands-on and require the participants to have a laptop with the Wireshark analyzer software installed.
Prerequisites
Knowledge of the IMS network architecture is assumed, as well as a general understanding of signalling principles in telecom networks. Attending APIS “IMS for VoLTE” course prior to this event, or having the equivalent knowledge, is necessary.
Brief overview of IMS network architecture
- IMS subscription: Service Profile and Filter Criteria
- IMS identities: IMPI, IMPU, GRUU, ICSI
- Roles of basic core IMS nodes: P-CSCF, I-CSCF, S-CSCF, SLF, HSS/UPSF and AS
- IMS breakout: BGCF, MGCF, MGW, ENUM roles
- Roles of IMS nodes for additional user plane handling functions: IMS-ALG/IMS-AGW, IBCF/TrGW, MRFC/MRFP, ATCF/ATGW
- Policy and Charging Control: PCRF, SPR
SIP and Diameter basics
- SIP addressing and routing functions, SIP and tel URI identifiers, SIP nodes, DNS usage
- SIP as an application layer protocol
- Diameter addressing and routing functions, Diameter Identity, DEA/DRA nodes, DNS usage
- Diameter as an application layer protocol
Birds-eye view of Voice over LTE profile for IMS (VoLTE)
- Life cycle of a UE in a VoLTE environment: power-up sequence, LTE Attach, PDN Connection Establishment, IMS Registration, Invitation, SRVCC
- Requirements on UE, the LTE and the IMS nodes
Impact of VoLTE on the network nodes
- VoLTE-specific parameters in HSS
- Identities used for call anchoring and for SRVCC: STN-SR, ATU-STI, C-MSISDN
- Functionalities and usage of TAS and SCC AS
Access Attach for VoLTE
- VoLTE-specific parameters and settings at LTE Attach and PDN Connection Setup
- APN and QoS recommendations for Default Bearers
IMS Registration for VoLTE
- IMS Registration : SIP extensions in VoLTE
- ATCF/ATGW inclusion at IMS Registration
- IMS Access Network Security: SIP extensions for AKA and IPsec
- The Registration traffic case with analysis of a trace
IMS Invitation for VoLTE
- IMS session setup: SIP extensions in VoLTE
- Service handling in IMS: TAS and Supplementary Services handling
- Access Domain Selection for voice call delivery decision: PS vs CS
- IMS QoS handling: SIP extensions for preconditions, Diameter on Gx and Rx for PCRF inclusion
- Session anchoring in ATCF/ATGW
- User Plane manipulation: transcoding, functions at the network border
- The IMS session setup traffic case with analysis of a trace
Single Radio Voice Call Continuity (SRVCC)
- Functions of network elements involved in SRVCC: ATCF/ATGW, SCC AS, enhanced MSC Server
- SRVCC Access Transfer: SIP extensions at IMS registration and session setup in enhanced SRVCC
- The SRVCC traffic case
A peek into VoLTE interworking
- Integrating CS domain with IMS: MSC Server enhanced for ICS
- A birds-eye view of the ICS procedures from the GERAN/UTRAN access
- Life cycle of a UE in a ICS environment: power-up sequence, CS Attach, PS Attach and PDP Context Activation, IMS Registration from the MSC, CS call anchored in IMS, rSRVCC
- A short discussion of the VoHSPA and VoWiFi options