Signalling Flows for the IP Multimedia Call Control in 3G

Wireless Network

Master’s Project

By

Sanjeev Kayath

Topics

• Introduction

• Packet Switched Core Network

• SIP

• Evolved Core Network

• Call flow

• Design and Implementation

• Results

Introduction

• 3G Wireless Network: – Core Network Architecture is changing.

• Drivers:– Demand for data and multimedia services in mobile

environment.

– Popularity of IP networks.

• Goal:– An all IP core network supporting data and multimedia

services in 3G wireless network.

Packet Switched Core Network

• GPRS– Introduced Packet Switching Network entities:

• Serving GPRS support node (SGSN)

• Gateway GPRS support node (GGSN)

– Mobile Station needs to perform• Attach and Detach procedure

• Context Activation procedure

Packet Switched Core Network

A simple block diagram of a packet switched network.

(Solid lines: Data transfer and Signaling interface. Dotted lines: Signaling Interface)

Mobile Station

Radio Access

SGSN GGSN Packet Network

Location Database

Session Initiation Protocol (SIP)

• Signalling Protocol to handle the multimedia call control.

• An application layer protocol to create and terminate multimedia sessions.

• Supports – User Location– User Capability– User Availability

• Messages: INVITE, ACK, BYE, REGISTER.

Evolved Core Network

• Include architectural entities that support the signalling messages to set up multimedia calls:– Call State Control Function (CSCF)

• User communicates with CSCF at application layer, using SIP messages.

• CSCF is equivalent to a SIP server.

• Signalling path is different from media flow path.

Evolved Core Network

A simple block diagram of a evolved packet switched network.

(Solid lines: Data transfer and Signaling interface. Dotted lines: Signaling Interface)

CSCF

Mobile Station

Radio Access

SGSN GGSN Packet Network

Location Database

Call Flow

• Entities in Signalling Path– User ( User Agent Client, User Agent Server)– Network

• Serving CSCF– Acts as a registrar.– Routes incoming and outgoing requests.

• Proxy CSCF– Immediate contact point of mobile station.

• HSS– Location Database.

GPRS Service Node GPRS Service Node

Proxy CSCF

Serving CSCF

Radio Network Controller

Serving CSCF

Proxy CSCF Radio Network Controller

Complete Signalling PathMobile Station Mobile Station

Base Station Base Station

Proxy CSCF

Serving CSCF Serving CSCF

Proxy CSCF

SIP Signalling PathMobile Station Mobile Station

• Entities actually involved in session set up/termination.

• Message exchange at the application layer, intermediate entities are not aware of these messages.

Design & Implementation

• Project simulates all the entities in the SIP signalling path and shows the end-to-end call set up.

• User and network entities interact at the application layer:– Use socket services– UDP transport protocol

Design & Implementation

• Platform: UNIX, Language: C++• Object Oriented Methodology:

– All the entities are objects.

• Main Objects:– User – ProxyCSCF– ServingCSCF– HSS

Design & Implementation

• User– Two Process:

• User Agent Client– Handles User Interface and initiates a call.

• User Agent Server– Listens for incoming calls.

– Synchronization:• Semaphore Locking.

Design & Implementation

• Network (Proxy and Serving CSCF)– Concurrent Server

• Fork a process to service incoming request.

• Main process loops infinitely to listen to incoming request.

– Synchronized access to database, HSS.• Semaphore locking.

Simulation Example

• Two Network Domains– ernie.ece.uic.edu– bert.ece.uic.edu

• Mobile Users– User1@ernie.ece.uic.edu– User2@bert.ece.uic.edu

• Definitions– Call Origination (Initiating user to ServingCSCF)– Call Termination (ServingCSCF to destination user)

Example Scenarios

• Scenario 1:– User1@ernie:

• Current Location: ernie, HOME

– User2@bert:• Current Location: ernie, ROAMING

• Scenario 2:– User1@ernie:

• Current Location: bert, ROAMING

– User2@bert:• Current Location: ernie, ROAMING

Scenario 1: Registration

Proxy CSCFServing CSCF

User1@ernie

User2@bert

HSS

Ernie Bert

Serving CSCF

HSS

Scenario 1: Registration

Proxy CSCFServing CSCF

User1@ernie

User2@bert

HSS

Ernie Bert

Serving CSCF

HSS

User1@ernie calls User2@bert

Proxy CSCFServing CSCF

User1@ernie

User2@bert

HSS

Ernie Bert

Serving CSCF

HSS

Simulation Example

• Features implemented– If User2@bert not registered, error returned.– If User2@bert busy, Destination busy returned.– On receiving call, User2@bert may accept the

call or reject the call.

• User1@ernie can hang up to terminate the session.

Proposed Change in the Signalling Path

• For Session Initiation, the signalling path may not include the ServingCSCF of the origination part.

• User profile can be downloaded to ProxyCSCF at the time of registration.

• ProxyCSCF performs the service control functionality instead of the ServingCSCF.

User1@ernie calls User2@bert

Proxy CSCFServing CSCF

User1@ernie

User2@bert

HSS

Ernie Bert

Serving CSCF

HSS

Results

• Proposed change results in decrease in Call Setup Delay.

• Caveat: Different Network Operators may not delegate service control to ProxyCSCF.

• Simulation demonstrates the signalling path for end-to-end call set up in “All IP” network.

Thank You !!