VoLTE Basic callflows in IMS network v2 - includes Registration, Basic VoLTE Call, SDP, Interconnect, Roaming, highlights important SIP headers for session routing and user identities.
ims registration call flow procedure volte sipVikas Shokeen
This PDF , VoLTE IMS Registration tutorial covers IMS Registration sip procedure in depth & Provides extract of 3GPP / GSMA Specs , I am covering below call flow in Depth :-
- LTE Attach & Default Internet EPS bearer
- Role of QCI-1 ( Voice ) , QCI-5 (SIP Signaling) , QCI-6 to 9 (Internet)
- Default Vs Dedicated Bearer in LTE
- Default IMS EPS bearer in LTE
- SIP and IMS Registration
- TAS Registration
VoLTE Flows and legacy CS network. Basic call routing to and from CS network using BGCF, MGCF, MGW. ENUM role in routing. IMS Cetralized Services (IMC) and SRVCC scenarios.
I have described VoLTE IMS Architecture in simplified way . Are you also finding 3GPP Specs complicated & Complex for VoLTE IMS . It covers Role played by individual Networks Elements as mentioned below :-
# VoLTE SIP Handset : SIP Support , UAC , UAS , User Agent , SIP-UA
# Underlying LTE Network : MME , SGW , PGW , PCRF , HSS , Dedicated Bearer , QCI , Default Bearer
# IMS Core : SIP Servers , P-CSCF , I-CSCF , S-CSCF , TAS , MMTEL , BGw , MRF , ATCF , ATGW , IBCF , MGCF , IM-MGW , TrGW
# Voice Core or PSTN Network for Break-in or Break-out Calls
It is a handbook of UMTS/LTE/EPC CSFB call flows.
This document is originally edited by Justin MA and it is free to share to everyone who are interested.
All reference/resource are from internet. If there is any copy-right issue, please kindly inform Justin by majachang@gmail.com.
Thanks for your reading!
ims registration call flow procedure volte sipVikas Shokeen
This PDF , VoLTE IMS Registration tutorial covers IMS Registration sip procedure in depth & Provides extract of 3GPP / GSMA Specs , I am covering below call flow in Depth :-
- LTE Attach & Default Internet EPS bearer
- Role of QCI-1 ( Voice ) , QCI-5 (SIP Signaling) , QCI-6 to 9 (Internet)
- Default Vs Dedicated Bearer in LTE
- Default IMS EPS bearer in LTE
- SIP and IMS Registration
- TAS Registration
VoLTE Flows and legacy CS network. Basic call routing to and from CS network using BGCF, MGCF, MGW. ENUM role in routing. IMS Cetralized Services (IMC) and SRVCC scenarios.
I have described VoLTE IMS Architecture in simplified way . Are you also finding 3GPP Specs complicated & Complex for VoLTE IMS . It covers Role played by individual Networks Elements as mentioned below :-
# VoLTE SIP Handset : SIP Support , UAC , UAS , User Agent , SIP-UA
# Underlying LTE Network : MME , SGW , PGW , PCRF , HSS , Dedicated Bearer , QCI , Default Bearer
# IMS Core : SIP Servers , P-CSCF , I-CSCF , S-CSCF , TAS , MMTEL , BGw , MRF , ATCF , ATGW , IBCF , MGCF , IM-MGW , TrGW
# Voice Core or PSTN Network for Break-in or Break-out Calls
It is a handbook of UMTS/LTE/EPC CSFB call flows.
This document is originally edited by Justin MA and it is free to share to everyone who are interested.
All reference/resource are from internet. If there is any copy-right issue, please kindly inform Justin by majachang@gmail.com.
Thanks for your reading!
VoLTE Voice over LTE Explained - Complete End to End VoLTE Overview - What is...Vikas Shokeen
Complete End to End Tutorial on Fundamentals & Basics of VoLTE , IMS Technology & VoLTE Overview ( Voice Over LTE )
- What is VoLTE
- Network Evolution to VoLTE
- How to Enable VoLTE in handset
- Differences between VoLTE & CSFB Call
- Voice call in LTE & VoLTE Networks
- Evolution of Voice Call
- VoLTE - Benefits for Users
- VoLTE - Benefits for Operators
- VoLTE Challenges
- Congestion handling for VoLTE Traffic
volte ims network architecture tutorial - Explained Vikas Shokeen
I have described VoLTE IMS Architecture in simplified way . Are you also finding 3GPP Specs complicated & Complex for VoLTE IMS . It covers Role played by individual Networks Elements as mentioned below :-
# VoLTE SIP Handset : SIP Support , UAC , UAS , User Agent , SIP-UA
# Underlying LTE Network : MME , SGW , PGW , PCRF , HSS , Dedicated Bearer , QCI , Default Bearer
# IMS Core : SIP Servers , P-CSCF , I-CSCF , S-CSCF , TAS , MMTEL , BGw , MRF , ATCF , ATGW , IBCF , MGCF , IM-MGW , TrGW
# Voice Core or PSTN Network for Break-in or Break-out Calls
Advanced: Control and User Plane Separation of EPC nodes (CUPS)3G4G
This presentation looks at Control and User Plane Separation of EPC nodes (CUPS) which was completed by 3GPP as part of Release 14 specifications and is set to be a key core network feature for many operators.
CUPS provides the architecture enhancements for the separation of functionality in the Evolved Packet Core’s SGW, PGW and TDF. This enables flexible network deployment and operation, by distributed or centralized deployment and the independent scaling between control plane and user plane functions - while not affecting the functionality of the existing nodes subject to this split.
VoLTE Voice over LTE Explained - Complete End to End VoLTE Overview - What is...Vikas Shokeen
Complete End to End Tutorial on Fundamentals & Basics of VoLTE , IMS Technology & VoLTE Overview ( Voice Over LTE )
- What is VoLTE
- Network Evolution to VoLTE
- How to Enable VoLTE in handset
- Differences between VoLTE & CSFB Call
- Voice call in LTE & VoLTE Networks
- Evolution of Voice Call
- VoLTE - Benefits for Users
- VoLTE - Benefits for Operators
- VoLTE Challenges
- Congestion handling for VoLTE Traffic
Circuit Switched Fallback (CSFB) is the most commonly used method to support voice services over Long Term Evolution (LTE) networks today, as the deployment of IP Multimedia Subsystem (IMS) is still in its infancy.
VoLTE Voice over LTE Explained - Complete End to End VoLTE Overview - What is...Vikas Shokeen
Complete End to End Tutorial on Fundamentals & Basics of VoLTE , IMS Technology & VoLTE Overview ( Voice Over LTE )
- What is VoLTE
- Network Evolution to VoLTE
- How to Enable VoLTE in handset
- Differences between VoLTE & CSFB Call
- Voice call in LTE & VoLTE Networks
- Evolution of Voice Call
- VoLTE - Benefits for Users
- VoLTE - Benefits for Operators
- VoLTE Challenges
- Congestion handling for VoLTE Traffic
volte ims network architecture tutorial - Explained Vikas Shokeen
I have described VoLTE IMS Architecture in simplified way . Are you also finding 3GPP Specs complicated & Complex for VoLTE IMS . It covers Role played by individual Networks Elements as mentioned below :-
# VoLTE SIP Handset : SIP Support , UAC , UAS , User Agent , SIP-UA
# Underlying LTE Network : MME , SGW , PGW , PCRF , HSS , Dedicated Bearer , QCI , Default Bearer
# IMS Core : SIP Servers , P-CSCF , I-CSCF , S-CSCF , TAS , MMTEL , BGw , MRF , ATCF , ATGW , IBCF , MGCF , IM-MGW , TrGW
# Voice Core or PSTN Network for Break-in or Break-out Calls
Advanced: Control and User Plane Separation of EPC nodes (CUPS)3G4G
This presentation looks at Control and User Plane Separation of EPC nodes (CUPS) which was completed by 3GPP as part of Release 14 specifications and is set to be a key core network feature for many operators.
CUPS provides the architecture enhancements for the separation of functionality in the Evolved Packet Core’s SGW, PGW and TDF. This enables flexible network deployment and operation, by distributed or centralized deployment and the independent scaling between control plane and user plane functions - while not affecting the functionality of the existing nodes subject to this split.
VoLTE Voice over LTE Explained - Complete End to End VoLTE Overview - What is...Vikas Shokeen
Complete End to End Tutorial on Fundamentals & Basics of VoLTE , IMS Technology & VoLTE Overview ( Voice Over LTE )
- What is VoLTE
- Network Evolution to VoLTE
- How to Enable VoLTE in handset
- Differences between VoLTE & CSFB Call
- Voice call in LTE & VoLTE Networks
- Evolution of Voice Call
- VoLTE - Benefits for Users
- VoLTE - Benefits for Operators
- VoLTE Challenges
- Congestion handling for VoLTE Traffic
Circuit Switched Fallback (CSFB) is the most commonly used method to support voice services over Long Term Evolution (LTE) networks today, as the deployment of IP Multimedia Subsystem (IMS) is still in its infancy.
While an increasing number of operators have already replaced their SS7 based telecommunication core network with a SIP based solution, the interconnection to neighboring partners is still often realized over an SS7 peering point. This means that a call that is carried over a VoIP network is translated to an SS7 call and then possibly back to VoIP again. The translation requires specialized components and resources, which increases the network operation costs and introduces unnecessary processing delay. To avoid these costs and delays operators have started introducing SIP based interconnection and peering points.
The ABC SBC enables operators to establish secure borders to their neighbors by offering topology hiding, denial of service protection and mediation in a scalable manner
Service Broker for VOIP IMA WebRTC and old telecom networksALTANAI BISHT
SB( Service Broker ) enables us to make use of existing applications and services from Intelligent Network’s SCP ( Service control Point ) , IMS’s Application Server as well as other sources in a harmonized manner .
Service broker is a service abstraction layer between the network and application layer in telecom environment.
This document describes the process of integrating a Service Broker with service harmonization and orchestration in a telco environment .
Rich Communication Suite (RCS) and RCS-e aims to seamlessly unify the communications experience by integrating traditional mobile telephony with new interactive services such as presence, instant messaging and content sharing enabled by the enhanced address book of the mobile phone.
LF Energy Webinar: Electrical Grid Modelling and Simulation Through PowSyBl -...DanBrown980551
Do you want to learn how to model and simulate an electrical network from scratch in under an hour?
Then welcome to this PowSyBl workshop, hosted by Rte, the French Transmission System Operator (TSO)!
During the webinar, you will discover the PowSyBl ecosystem as well as handle and study an electrical network through an interactive Python notebook.
PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
- A fully editable and extendable library for grid component modelling;
- Visualization tools to display your network;
- Grid simulation tools, such as power flows, security analyses (with or without remedial actions) and sensitivity analyses;
The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
What you will learn during the webinar:
- For beginners: discover PowSyBl's functionalities through a quick general presentation and the notebook, without needing any expert coding skills;
- For advanced developers: master the skills to efficiently apply PowSyBl functionalities to your real-world scenarios.
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
State of ICS and IoT Cyber Threat Landscape Report 2024 previewPrayukth K V
The IoT and OT threat landscape report has been prepared by the Threat Research Team at Sectrio using data from Sectrio, cyber threat intelligence farming facilities spread across over 85 cities around the world. In addition, Sectrio also runs AI-based advanced threat and payload engagement facilities that serve as sinks to attract and engage sophisticated threat actors, and newer malware including new variants and latent threats that are at an earlier stage of development.
The latest edition of the OT/ICS and IoT security Threat Landscape Report 2024 also covers:
State of global ICS asset and network exposure
Sectoral targets and attacks as well as the cost of ransom
Global APT activity, AI usage, actor and tactic profiles, and implications
Rise in volumes of AI-powered cyberattacks
Major cyber events in 2024
Malware and malicious payload trends
Cyberattack types and targets
Vulnerability exploit attempts on CVEs
Attacks on counties – USA
Expansion of bot farms – how, where, and why
In-depth analysis of the cyber threat landscape across North America, South America, Europe, APAC, and the Middle East
Why are attacks on smart factories rising?
Cyber risk predictions
Axis of attacks – Europe
Systemic attacks in the Middle East
Download the full report from here:
https://sectrio.com/resources/ot-threat-landscape-reports/sectrio-releases-ot-ics-and-iot-security-threat-landscape-report-2024/
Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
"Impact of front-end architecture on development cost", Viktor TurskyiFwdays
I have heard many times that architecture is not important for the front-end. Also, many times I have seen how developers implement features on the front-end just following the standard rules for a framework and think that this is enough to successfully launch the project, and then the project fails. How to prevent this and what approach to choose? I have launched dozens of complex projects and during the talk we will analyze which approaches have worked for me and which have not.
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
The publishing industry has been selling digital audiobooks and ebooks for over a decade and has found its groove. What’s changed? What has stayed the same? Where do we go from here? Join a group of leading sales peers from across the industry for a conversation about the lessons learned since the popularization of digital books, best practices, digital book supply chain management, and more.
Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
PHP Frameworks: I want to break free (IPC Berlin 2024)Ralf Eggert
In this presentation, we examine the challenges and limitations of relying too heavily on PHP frameworks in web development. We discuss the history of PHP and its frameworks to understand how this dependence has evolved. The focus will be on providing concrete tips and strategies to reduce reliance on these frameworks, based on real-world examples and practical considerations. The goal is to equip developers with the skills and knowledge to create more flexible and future-proof web applications. We'll explore the importance of maintaining autonomy in a rapidly changing tech landscape and how to make informed decisions in PHP development.
This talk is aimed at encouraging a more independent approach to using PHP frameworks, moving towards a more flexible and future-proof approach to PHP development.
Builder.ai Founder Sachin Dev Duggal's Strategic Approach to Create an Innova...Ramesh Iyer
In today's fast-changing business world, Companies that adapt and embrace new ideas often need help to keep up with the competition. However, fostering a culture of innovation takes much work. It takes vision, leadership and willingness to take risks in the right proportion. Sachin Dev Duggal, co-founder of Builder.ai, has perfected the art of this balance, creating a company culture where creativity and growth are nurtured at each stage.
Kubernetes & AI - Beauty and the Beast !?! @KCD Istanbul 2024Tobias Schneck
As AI technology is pushing into IT I was wondering myself, as an “infrastructure container kubernetes guy”, how get this fancy AI technology get managed from an infrastructure operational view? Is it possible to apply our lovely cloud native principals as well? What benefit’s both technologies could bring to each other?
Let me take this questions and provide you a short journey through existing deployment models and use cases for AI software. On practical examples, we discuss what cloud/on-premise strategy we may need for applying it to our own infrastructure to get it to work from an enterprise perspective. I want to give an overview about infrastructure requirements and technologies, what could be beneficial or limiting your AI use cases in an enterprise environment. An interactive Demo will give you some insides, what approaches I got already working for real.
GraphRAG is All You need? LLM & Knowledge GraphGuy Korland
Guy Korland, CEO and Co-founder of FalkorDB, will review two articles on the integration of language models with knowledge graphs.
1. Unifying Large Language Models and Knowledge Graphs: A Roadmap.
https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
Search and Society: Reimagining Information Access for Radical FuturesBhaskar Mitra
The field of Information retrieval (IR) is currently undergoing a transformative shift, at least partly due to the emerging applications of generative AI to information access. In this talk, we will deliberate on the sociotechnical implications of generative AI for information access. We will argue that there is both a critical necessity and an exciting opportunity for the IR community to re-center our research agendas on societal needs while dismantling the artificial separation between the work on fairness, accountability, transparency, and ethics in IR and the rest of IR research. Instead of adopting a reactionary strategy of trying to mitigate potential social harms from emerging technologies, the community should aim to proactively set the research agenda for the kinds of systems we should build inspired by diverse explicitly stated sociotechnical imaginaries. The sociotechnical imaginaries that underpin the design and development of information access technologies needs to be explicitly articulated, and we need to develop theories of change in context of these diverse perspectives. Our guiding future imaginaries must be informed by other academic fields, such as democratic theory and critical theory, and should be co-developed with social science scholars, legal scholars, civil rights and social justice activists, and artists, among others.
Software Delivery At the Speed of AI: Inflectra Invests In AI-Powered QualityInflectra
In this insightful webinar, Inflectra explores how artificial intelligence (AI) is transforming software development and testing. Discover how AI-powered tools are revolutionizing every stage of the software development lifecycle (SDLC), from design and prototyping to testing, deployment, and monitoring.
Learn about:
• The Future of Testing: How AI is shifting testing towards verification, analysis, and higher-level skills, while reducing repetitive tasks.
• Test Automation: How AI-powered test case generation, optimization, and self-healing tests are making testing more efficient and effective.
• Visual Testing: Explore the emerging capabilities of AI in visual testing and how it's set to revolutionize UI verification.
• Inflectra's AI Solutions: See demonstrations of Inflectra's cutting-edge AI tools like the ChatGPT plugin and Azure Open AI platform, designed to streamline your testing process.
Whether you're a developer, tester, or QA professional, this webinar will give you valuable insights into how AI is shaping the future of software delivery.
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What is VoLTE?
LTE
Tel: num1 Tel: num2
GSM
Tel: num3
• VoLTE stands for Voice over LTE. LTE is a new standard for wireless communication
of high-speed data for mobile phones. ViLTE means Video over LTE.
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What is in the LTE?
4
LTE
• A packet-switched all-IP network which provides data connectivity and mobility.
• LTE access network doesn’t provide any voice, video or text services. This is to be handled by
IMS.
e-nodeB
e-nodeB
EPC
MME SGW
PGW
E-UTRAN
HSS
UE
• We will not discuss LTE RAN and EPC in this training.
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IMS
5
LTE
• VoLTE is based on the IP Multimedia Subsystem (IMS) network – a framework designed for
delivering IP multimedia services.
• IMS is access independent, user-centric network providing services such as authentication,
session routing and management, QoS, roaming, provisioning, charging etc.
LTE
IMS
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4G Ecosystem
• The Fourth Generation of Mobile Networks is based on IP protocol. From Operator point of view it is a
huge change
• New Radio Network
• New Enhance Packed Core
• New Service Network – IMS
• New Protocols, Flows, KPIs, Vendors, New Issues
• 4G is user centric and supports multiple access networks
• We can connect to IMS using any IP-based access network
• A-SBC provides connectivity, security, NAT/NAT traversal, media handling etc.
• IMS is integrated also with the legacy (Sigtran) network
• VoWifi (GSMA IR.51) provides the same set of services as VoLTE and is integrated using EPC.
• RCS UP is integrated with VoLTE/VoWifi.
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IP-based Communication
• Separates Signaling (SIP, H.323, XMPP, REST, ..) and Media (RTP, MSRP, WS, HTTP, ..) flows.
• The purpose of Signaling is to
• Locate the recipient
• Share presence information
• Exchange the parameters of the multimedia session
• Binding between IP and User Identity is created during Registration.
• One user can use multiple different identities and devices/sw clients.
For VoLTE
• SIP is used for end-to-end signaling, RTP for Voice/Video
• Public User Identity (IMPU) is based on telephone number can be e.g.
• sip: +<number>@volte.ims.mnc012.mcc345.3gppnetwork.org
• tel: +<number>
• Binding between actual IP assigned by LTE (PGW) and IMPU is stored in IMS Network (S-CSCF)
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What is ?
• The standard is defined by GSMA in IR.92 and IR.94 as a minimum mandatory set of features for an interoperable,
high quality IMS-based telephony service and SMS over LTE network.
The scope includes:
• IMS basic capabilities and supplementary services for telephony
• Real-time media negotiation, transport, and codecs
• LTE radio and evolved packet core capabilities
• Functionality that is relevant across the protocol stack and subsystems
• Additional features that need to be implemented for the UEs and networks that wish to support concurrent Circuit
Switched (CS) coverage
Description of basic call flows and procedures can be found in VoLTE Service Description and Implementation Guide.
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IMS
LTE
• VoLTE is based on the IP Multimedia Subsystem (IMS) network – a framework designed for
delivering IP multimedia services.
• IMS is access independent, user-centric network providing services such as authentication,
session routing and management, QoS, roaming, provisioning, charging etc.
IMS
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IMS Entities I
Proxy - Call Session Control Function (P-CSCF)
• First point of contact for SIP signaling within IMS network
• Can be located in a visited as well as in a home network
• Often deployed as a part of Access Session Border Controller (A-SBC)
• Authorizes media plane resources, interacts with access network via PCRF
• May encrypt communication using IPSec or TLS sessions
Interrogating-CSCF (I-CSCF)
• Contact point in the home network
• The most important functionality is to provide location service - localization of an S-CSCF based on received
name or capabilities from the HSS for a particular subscriber
Serving-CSCF (S-CSCF)
• SIP server responsible for registration and routing within IMS network
• Along with P-CSCF assigned to user for the whole duration of registration
• Based on service profile received from HSS triggers ASs, maintains AS associations
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IMS Entities II
Telephony Application Server (TAS)
• Application server is responsible for telephony services which can be applied
• Provides address normalization, call diverting, call forwarding, barring, triggers playing of
tones/announcements, creates billing records, etc.
• TAS can retrieve subscriber profile from HSS, can communicate also with CS network elements over Camel.
• TAS is what makes the VoLTE enhancements on top of the pure VoIP
Multimedia Resource Function (MRF)
• Media Server which can play tones and announcements (early media).
• Supports conferencing services where acts as a mixer.
IP-SM-GW
• Application server which provides Transport Level Interworking for SMS sent over IP.
• SMS service still provided by SMSC in CS network.
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IMS Databases
DNS
• Provides routing on SIP layer
• Important for load-sharing and failover scenarios
• Enables zero-configuration using service discovery
ENUM
• Used for Mobile Number Portability (MNP)
• Can be used for routing towards CS network
Home Subscriber Server (HSS)
• Enables routing on service layer
• Contains all information about subscribers and their services
• The only persistent storage, hence crucial for failover/restoration scenarios
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IMS Registration
Purpose
• Authenticate Subscriber
• Encrypt communication channel
• Create a binding between IMPU and actual location (Contact address)
• Update soft-state presence information
• Learn capabilities of a particular device
• Create a linkage between S-CSCF and P-CSCF
Key Facts
• All the devices belonging to a particular subscriber are handled by one S-CSCF
• One S-CSCF and one P-CSCF are assigned to UE for the whole duration of registration
• Registration data is stored in HSS and can be used in Restoration Scenarios
• S-CSCF can provide “Implicit Registration” to other IMPUs which are listed in subscriber profile
• If Registration doesn’t work, other callflows don’t work either. Therefore the Registration is the most
important scenario!
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How to Call?
RTP
UASUAC
SIP INVITE (SDP-O)
Terminating
Network
Originating
Network
P-CSCF
S-CSCF
I-CSCF
A-SBC
O-TAS IPSMGW
DNS
HSS
DNS
HSS
P-CSCF
S-CSCF
I-CSCF
T-TAS
A-SBC
ALG/AGWALG/AGW
realtimecommunications.wordpress.com
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IMS Session Setup
Purpose
• Set up a signaling path
• Exchange parameters of the multimedia session
• Allocate resources in access networks and on SBCs
• Trigger TAS to apply originating and terminating services
Key Facts
• There are always two TASes and two IMS Cores on the signaling path. Although physically they can be the
same servers, logically we have to distinguish the originating and terminating network elements
• Routing towards ASs is driven by IFC (part of the Subscriber Profile)
• Originating S-CSCF provides routing towards terminating network
• IMS Network (domain) is represented by I-CSCF. The translation (domain -> IP) is done by DNS. I-CSCF
implements Location Service
• Both TAS and S-CSCF can modify R-URI. Both can also trigger ENUM
• In case S-CSCF can’t find the routing in IMS (e.g. because of tel uri in R-URI), the message is routed to CS (via
BGCF and MGCF)
• Terminating S-CSCF updates R-URI with the Contact information
realtimecommunications.wordpress.com
RTP
UASUAC
P-CSCF
S-CSCF
I-CSCF
O/T-TAS IPSMGW
DNS
HSS
ALG/AGW
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CS related flows
Facts
• Not everywhere we have strong LTE signal
• Many devices still don’t support 4G
• Operators invested a lot in 3G infrastructure
• Not all the services are supported or transferred in
4G network
Solution
MSS
CS
IMS
P-CSCF
A-SBC
AGW
MGW
LTE
S-CSCF
I-CSCF
T-TAS
DNS
HSS
PGW
SGW
MSC
MGCF
IM-MGW
eMSC
realtimecommunications.wordpress.com
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• IMS supports interworking with legacy network via MGCF/MGW
• Routing towards particular MSC is performed by BGCF
• Our aim is to centralize services in IMS – that means even those subscribers who are currently in CS
network will be handled by IMS. IMS Centralization (IMC) is provided by a dedicated application
server – SCC AS
• SCC AS does also support Voice Call Continuity. That is Access Transfer during an active call.
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And how does it work in practice?
Access Site
R4
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Core Site A
P-CSCF
S-CSCF
I-CSCF
A-SBC
O-TAS IPSMGW
DNS
HSS
S-CSCF
I-CSCF
T-TAS
ATGW
I-SBC
Access site R1
Access Site
R5
Access Site
R2
Access Site
R3
RCS
MRF
BGCF
MGCF
MSC
MGW
PSXDMS
Core Site B
E-CSCF
DSC
MRF
BGCF
E-CSCF
IPSMGW
ATCF
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Take Away
• VoLTE provides telecommunication services using IMS network.
• IMS provides a framework for basic services such as User Identities, Authentication, Session Routing and Session
Control, Service Triggering etc.
• Basic IMS entities are A-SBC, P-CSCF, CSCF, DNS, HSS, Application Servers.
• For Signaling IMS mandates SIP protocol. The purpose of signaling is to locate the recipient.
• In order to create a binding between actual point of presence (IP) and user identity (tel/sip uri) all users have to
register first.
• Multimedia data goes out of band using RTP.
• The GSMA/3GPP standards define the signalling Call Flows, along with the content and syntax of the protocol
headers, see: VoLTE Service Description and Implementation Guide or GSMA IMS Profile for Converged IP
Communications.
