Voice over Long Term Evolution (VoLTE) and the IMS (VOLTE)

1. IMS Architecture & 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

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

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)

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

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?

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

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

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)

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?

10. SIP Route Headers

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

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

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

13. H.248

• Overview
  • H.248 Call Flow Example
  • H.248 Common Controller
  • H.248 Call Control Model
• H.248 in the IMS Core
  • H.248 Call Control Model

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

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)

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
  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
  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
  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
  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
  21. Emergency Call Flow
  • References
    • 3GPP Emergency
  • Components
    • IMS Emergency Sessions Topology and Message Flow
    • IP Multimedia Subsystem (IMS) Emergency Sessions Call Flow
  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
  23. DNS
  • Zone File
    • DNS root zone has 13 named authorities
    • How a Zone file appears in Linux – Bind9
    • How $ORIGIN Impacts the Zone File
    • Sample Zone File Organized into a Table (strictly for teaching)
    • “SOA” Record – The Start of Authority
  • Locating SIP Servers
    • NS-record
    • A-record
    • SRV-record
    • NAPTR – Naming Authority Pointer
    • RFC 3263 – Locating SIP Servers - NAPTR
    • RFC 3263 – Locating SIP Servers - SRV
    • RFC 3263 – Locating SIP Servers - A-record
    • RFC 3263 – Locating SIP Servers – INVITE
  LABS: Wireshark Traces, Call Flows & Examples
  • Lab 0. Understanding the Lab Environment
  • Lab 1. Using Wireshark
  • Lab 2. SIP User Agent Configuration
  • Lab 3. Direct UA to UA Routing with No Proxy
  • Lab 4. Proxy Based SIP Routing
  • Lab 5. Adding Authorized UAs to a Domain
  • Lab 6. Registering a SIP UA (Capturing a SIP REGISTER with Wireshark)
  • Lab 7. Intra Domain Routing (SIP routing within the same domain)
  • Lab 8. Inter Domain Routing (SIP routing to different domains)
  • Lab 9. Digit translation
  • Lab 10. Prefix domain transfer (PDT) management
  • Lab 11. Capturing a “normal’ SIP call via Wireshark
  • Lab 12. Capturing a call to a vacant seat via Wireshark
  • Lab 13. Capturing a call to a busy seat via Wireshark
  • Lab 14. Capturing a call-forward (3xx response) via Wireshark
  • Lab 15. Via, Route, and Record-Route headers
  • Lab 16. Examining and manipulating Max-Forwards header
  • Lab 17. Capturing SDP offer and answer
  • Lab 18. Silence suppression
  • Lab 19. DTMF RFC 2833 and SIP INFO
  • Lab 20. SIP Back-to-Back UA configuration example (Asterisk)
  • Lab 21. REGISTER SIP device to Back-to-Back UA
  • Lab 22. Capture SIP call through a Back-to-Back UA and compare to a Proxy
  • Lab 23. RTP Relay
  • Lab 24. Real-Time Control Protocol (RTCP)
  • Lab 25. Routing with DNS / ENUM
  • Lab 26. Testing Connectivity using SIP OPTIONS
  • Lab 27. SIP testing with SIP-p
  • Lab 28: IMS Service Profile
  • Lab 29: Roaming
  • Lab 30: Exploring the Home S-CSCF Set
  • Lab 31: Registration Termination Request (RTR)
  • Lab 32: Push Profile Request