IMS Signalling for VoLTE

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.

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.

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.

‘THE COURSE IS GOOD.’

Protocol Senior Engineer at SIDIA (Samsung Instituto de P&D da Amazonia), Brazil

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