VoLTE and the IMS

Course Code: 6001

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What you'll learn
Outline
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Who should attend

Overview

This intensive five-day course trains participants in Voice over Long Term Evolution (VoLTE), IP Multimedia Subsystem (IMS) and the Session Initiation Protocol (SIP). The course covers call flow through the EU-TRAN, the EPC and into the IMS core. The course encompasses call flows and live labs using the IMS platform. It also covers other associated technologies, such as, Diameter and DNS to help participants get a thorough understanding of all concepts.

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Course Delivery

This course is available in the following formats:

Live Classroom
Duration: 5 days

Live Virtual Classroom
Duration: 5 days

What You'll learn

Introduction to VoLTE
Understanding the 3GPP
Exploring the core concepts of IMS
Understanding visited network vs. home network
Working with commonly utilized bearers
Understanding the handovers between eNodeBs
Delving into the depths of the SIP architecture
Discovering the basic SIP and IMS specific headers
Understanding diameters, and diameter vs. radius
Understanding the Presence Model
Exploring the Session Description Protocol (SDP)
Learning how to enforce the QoS
Exploring the circuit switched fallback
Understanding DNS

Outline

Module 1: IMS architecture and SIP proxies

Standards Bodies
- Understanding the 3GPP
- 3rd Generation Partnership Project
- The Network Operators Strike Back: ETSI TISPAN NGN, 3GPP2, & Cablelabs
- IETF & RFCs
VoLTE Introduction
- VoLTE + IMS Advantages
- Legacy vs. IMS
- Traditional User Database Management
- Why VoIP Central Control Can Not Compete with IMS
- The 3GPP IMS Architecture
- VoLTE and IMS Architecture Analysis
The Building Blocks
- The IMS Core (IP Multimedia Subsystem)
- IMS Core Components
- IBCF and TrGW
- The HSS (Home Subscriber Server)
- The SLF (Subscription Locator Function)
- The EPC (Evolved Packet Core)
- The E-UTRAN (Evolved UMTS Radio Access Network)
- The UTRAN (UMTS Terrestrial Radio Access Network)
- PCRF
- PCRF and its Interfaces
Call Control Paths
- The SERVICE PATH = The Half Call – AS Formed by the SIP REGISTRATION
- An IMS to IMS Call Analysis
- Call Control and Media Paths
- The IMS Half Call Concept
- Application Servers (AS)
- Serving Call Session Function (S-CSCF)
Roaming and Visited
- Visited Network vs. Home Network
- Proxy Call Session Function (P-CSCF)
- S5 (Local Breakout) and Registration
- S8 Access and Registration
VoLTE Access
- Intro to Bearers & APNs
- The Evolved Packet Core Component Analysis
- PDCP, RLC, MAC, PHY, and the LTE Grid
Call Flow
- Intra Domain Service Path Originating
- Intra Domain Service Path Terminating
- Intra Domain Call
- Intra Domain Routing
- Intra Domain Routing Decision
- Intra Domain Call End to End
- Inter-domain Call, Intra-domain Service Paths
- Inter-domain Call Routing
- Cross Domain Routing Decision
- IMS Border Control Function and Transition Gateway
- Inter-domain Roaming
- Inter-domain Call While Roaming
- Both UEs Roaming Plus Inter-Domain Call
- Both UEs Roaming Plus Inter-Domain Call Control Path

Module 2: IMS Identifiers

IMS IDs
- IMS Identifiers
- UML Model of the Data Downloaded over Cx Interface
UICC
- UICC (Universal Integrated Circuit Card)
IMS URI
- IMSI – International Mobile Subscriber Identity [im-zee]
- IMS Specific Numbering, Addressing and ID
- Home Network Domain Name

Module 3: VoLTE and IMS Architecture

HSS
- The HSS (Home Subscriber Server)
- The SLF (Subscription Locator Function)
- CSCF (Call/Session Control Function)
- P-CSCF (Proxy-Call/Session Control Function)
- I-CSCF (Interrogating-Call/Session Control Function)
- S-CSCF (Serving-Call/Session Control Function )
- Breakout Gateway Control Function (BGCF)
- AS (Application Server)
- MRF – MRFC / MRFP (Media Resource Function Controller / Processor)
- Policy and Charging Rules Function and the EPC
- Mobility Management Entity (MME)
- Serving Gateway (S-GW)
- PDN Gateway (P-GW)

Module 4: Bearer and APNs

Commonly Utilized Bearers
- Bearer Components from the E-UTRAN through the EPC
- VoLTE Bearers from the E-UTRAN through the EPC
Internet Bearers from E-UTRAN through the EPC

Module 5: Power up Process

Overview
- Frequency Scanning and UE Categories
System Acquisition and RRC Connection Setup
- Primary Synchronization Signal (PSS)
- Cell-ID & Secondary Synchronization Signal (SSS)
- Physical Broadcast Channel (PBCH)
- Master Information Block (MIB)
- Transport Downlink Shared Channel (DL-SCH) for SIB1
- System Information Block type 1 (SIB1)
- Downlink Shared Channel (DL-SCH) & SIB2
- Uplink Synchronization
- RRC CONNECTED and RRC IDLE
- SIB1 – SIB12
- Cell Selection
Network Attach
- The IMS APN Bearer Establishment
- Attach Request, NAS, Authentication Process
- Encryption and ESM Info
- Location Request and Response
- Create Session Request and Response
- CCR AAA Request and Response
- Create Session Response SGW to MME to eNB
- Initial Context Setup and RRC Reconfiguration
- UE Capability and ICR
- Modify Bearer and EMM Info
- Modify Bearer Response, AAA Responses and the SIP REGISTER
- The Spreading Sequence
- How does a UE request bandwidth in order to gain access to request bandwidth?

Module 6: Handover Between eNodeBs

Idle Mode
- Cell Reselection
- Discontinuous Reception (DRX) with Long and Short DRX
- How DRX Timers Apply the LTE Grid
- Idle Mode Within and Beyond the UE
Active UE
- Intra-frequency Mobility (3GPP TS 23.401)
- Intra MME SGW Handover Using the X2 Interface
- S1-based Handover with S-GW & MME Relocation

Module 7: Tracking and Paging A UE

Overview
- Tracking Area Defined
- Tracking Area Identifiers
- Tracking Area Lists
- Relationship of MME Pool Areas, TA, and S-GW Service Areas
Tracking and Paging a UE
- Tracking Area Update (TAU)
- Idle Mode
- UE Entering Idle Mode
- Paging an Idle UE

Module 8: SIP Architecture

The Big Picture
- Key VoLTE and IMS Protocols
SIP Message Format
- SIP User Agent (UA)
- SIP Request and Response Format
IMS SIP Transactions
- SIP Requests (Methods)
- SIP Response Codes
- A SIP Transaction Defined
- PRACK and The 100rel Process (RFC 3262)
- VoLTE to VoLTE SIP Transactions
SIP Control Path
- Trust Chain
- SIP Architecture
- B2BUA Example: TAS
- Mapping SIP dialogs through an Application Server
Proxy vs. B2BUA
- User Identities: Address-of-Records and Contact-URIs
SIP URI
- SIP and SIPS URI Structure Components (RFC 3261)

Module 9: SIP Via Paths

The Via Header
- The “Via:” Path: How A Response Finds Its Way Back
The SIP Transaction
- Via: Lifetime = per Transaction! (Not the Entire Duration of the Dialog)
Impact of Via Path on the SIP Dialog
- What Path Does the ACK Take?

Module 10: SIP Route Headers

RR and Route
- The Record-Route and Route Function
Looping
- Loop Detection

Module 11: Basic SIP & IMS Specific Headers

Start Line
Via:
Via: branch parameter
From:
To:
Call-ID:
SIP Dialog ID
Contact:
CSeq: (Command Sequence)
Content-Type:
- Content-Type: message/sipfrag RFC 3420
- Content-Length:
Max-Forwards:
Allow:
OPTIONS
User-Agent:
Supported:
P-Preferred-Identity: and Privacy: RFC 3325 (UA to P-CSCF)
P-Preferred-Identity: to P-Asserted-Identity:
P-Access-Network-Info: RFC 3455
Authorization: RFC 3261 Section 22.2
Path: RFC 3327
Service-Route: RFC 3608
Introduction to SigComp
- SigComp Example

Module 12: Diameter

Overview
- RADIUS vs DIAMETER
- Diameter Protocol
Diameter Message Structure
- The AVP Chain: Type – Length – Value
- AVPs Encapsulated Inside an AVP
- Diameter Header Structure
- AVP Structure
- Diameter Message Example
- Diameter Message as Wireshark Would Display it
Customization
- Diameter Code Customization
- IMS’s Diameter Cx Command Codes Values
- Diameter AVPs Defined for the Cx Interface
- Diameter AVPs: Rx Interface Codes
Registration Call Flow
- Challenge
- Authorization
- Registration Status
- Registration Termination Request
- Registration Status at the P-CSCF
SCTP
- Traditional Transport Layers (OSI Layer 4)
- Stream Control Transmission Protocol (RFC 4960)
- SCTP High Durability Connections
- Setting Up An Association
- The SCTP Protocol Data Unit
- Head-of-Line-Blocking Avoidance
- Chunking & Bundling

Module 13: H.248

Overview
- 248 Call Flow Example
- 248 Common Controller
- 248 Call Control Model
248 in the IMS Core
- 248 Call Control Model

Module 14: Initial Filter Criteria (iFC)

iFC Function
iFC Logic
Data Structure
- UML Model of the Data Downloaded Over Cx Interface
iFC Logic
- Disjunctive Normal Form
- Conjunctive Normal Form
iFC Example
- Setting Up A TAS for Feature Enablement – (Using three.ims Domain)
- Service Profile

Module 15: Presence

The Presence Model
- Presentity and Watcher
- PUBLISH
- SUBSCRIBE
- NOTIFY
IMS Call Flow
- Cross Domain SUBSCRIBE Example
- PUBLISH presentity and Cross Domain NOTIFY to Watchers
Basic vs. Rich Presence
- Presence Information Data Format (PIDF) RFC 3863
- Rich Presence Information Data format (RPID) RFC 4480
Message Examples
- PUBLISH (Initial)
- SUBSCRIBE (Watcher)
- NOTIFY (Initial Status)
- PUBLISH (Updated status)
- NOTIFY (Updated status)

Module 16: Session Description Protocol (SDP)

Overview
- SDP Establishes ½ the Media Channel
- SDP: RFC 4566
- RTP is “simplex”
- a=sendonly means what?
- Media Direction’s Impact on RTCP
Lines
- Version, v=
- Origin, o=
- Session, s=
- Connection, c=
- Time, t=
- Media Description, m=
- Bandwidth, b=
- The “a=” Attribute Header (Extends SDP)
- Attribute, a=fmtp, Format Specific Parameters
- Mode
- Packet Interval
Offer/Answer
- Overview of Offer/Answer
- OFFER/ANSWER Examples
- SDP Offer/Answer Model
- UPDATE RFC 3311
Preconditions
- Preconditions; a=curr and a=des
- Preconditions Call Flow
- Preconditions E2E and Segmented

Module 17: QoS

Enforcing QoS
- Linking the IMS Core to the EPC
- PCRF Interfaces: Sp Ud, Np, Rx, Sy, Gy, Gyn, Gzn, Gz, Sd, Gx, Gxx
- 3GPP Policy Architecture (Simplified)
- Roaming scenarios: H-PCRF and V-PCRF
- PGW Gate/Pinhole Defined
- Converting SDP to a Gate
- VoIP Service Requirements and the QoS Solution
- Default Bearer, Dedicated Bearer, QCI, ARP, GBR
- Rx and Gx Messages
- IMS Dedicated Bearer Setup
- LTE Dedicated Bearer Setup AAR, CCR, Create Bearer Req

Module 18: IMS Call Flow Examples

SIP REGISTER
- Initial IMS REGISTRATION
- IMS SIP Registration and the DIAMETER Query
- IMS SIP Registration and DIAMETER Response
- IMS SIP Registration REGISTRATION to SCSCF
- IMS SIP Registration aka MD5 CHALLENGE (401)
- IMS SIP Registration Challenge Response
- IMS SIP Registration Confirmed; 200
- IMS SIP Registration; SERVICE PATH Determination
De-Registration
- UE Initiated De-Registration
- Network Initiated De-Registration
Media Relay
- IMS Call Setup with Media Relay
- Terminal Initiated Session Release

Module 19: Circuit Switched Fallback

CSFB Originating
- 3G and 4G Update Message Review: LAU, TAU, RAU
- Combined EPS/IMSI Message
- How SR-VCC Interoperates with the Combined Attach
- Extended Service Request
- Connection Management Service Request
CSFB Terminating
- The IAM and Paging
- Service Request and Context Mod with CSFB
- CCO and Context Release
- Suspend an Update Bearers
- Paging Response
- Active Call
Ladder Diagram
- CSFB Ladder Diagram End to End

Module 20: SR-VCC

Overview
- Comparing VCC, ICS, and IMS-SC
- Apply VCC, ICS, and IMS-SC technology to CSFB and SR-VCC
Routing Number
- Mobile Station International Subscriber Directory Number (MSISDN)
- Routing Number
- Which number “Wins” when Routing?
- Which number does the server need?
- STN-SR, IMRN, and gsmSCF Routing Numbers
- How MSISDN and STN are included in SIP messages
SR-VCC Control Paths
- Services that must be optimized for SRVCC
The Media Path
- Direct Media
- The Role of the ATCF/ATGW and Media Anchoring
- Interoperation between ATCF/ATGW and MSC (4G to 3G Media)
- SR-VCC example: UTRAN to UTRAN Call Control and Media Paths
- Interfacing SR-VCC with a MSC not optimized for SRVCC
SR-VCC Call Flow
- SR-VCC PS to CS Transfer Message by Message
- SRVCC PS to CS Transfer
- Control and Media Paths Following SR-VCC-controlled PS to CS Transfer
- SRVCC from E-UTRAN to GERAN without DTM Support

Module 21: Emergency Call Flow

References
- 3GPP Emergency
Components
- IMS Emergency Sessions Topology and Message Flow
- IP Multimedia Subsystem (IMS) Emergency Sessions Call Flow

Module 22: Charging in the IMS

Charging Systems Overview
- Charging in the IMS
- IMS Charging Mechanisms
- Charging Interworking Functions & Reference Points
- Offline Charging Functions
- Online Charging Functions
- Online (Ro) and Offline (Rf) Charging Commands
Charging and Call Flow
- P-Charging-Vector: RFC 3455
- P-Charging-Function-Addresses
- IMS Call Setup

Module 23: DNS

Charging Systems Overview
- Charging in the IMS
- IMS Charging Mechanisms
- Charging Interworking Functions & Reference Points
- Offline Charging Functions
- Online Charging Functions
- Online (Ro) and Offline (Rf) Charging Commands
Charging and Call Flow
- P-Charging-Vector: RFC 3455
- P-Charging-Function-Addresses
- IMS Call Setup