Transcript Signalling Flows for the IP Multimedia Call Control in 3G Wireless

Signalling Flows for the IP
Multimedia Call Control in 3G
Wireless Network
Master’s Project
By
Sanjeev Kayath
Topics
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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
Mobile
Station
Radio
Access
SGSN
GGSN
Packet
Network
Location
Database
A simple block diagram of a packet switched network.
(Solid lines: Data transfer and Signaling interface. Dotted lines: Signaling Interface)
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
Mobile
Station
Radio
Access
SGSN
Location
Database
GGSN
Packet
Networ
k
CSCF
A simple block diagram of a evolved packet switched network.
(Solid lines: Data transfer and Signaling interface. Dotted lines: Signaling Interface)
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.
Complete Signalling Path
Mobile Station
Mobile Station
Serving CSCF
Serving CSCF
Base Station
Base Station
Radio Network Controller
GPRS Service Node
Proxy CSCF
Proxy CSCF
Radio Network Controller
GPRS Service Node
SIP Signalling Path
Mobile Station
Mobile Station
Serving CSCF
Proxy CSCF
Serving CSCF
Proxy CSCF
• 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:
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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
– [email protected]
– [email protected]
• 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
User1@ernie
Serving CSCF
Serving CSCF
Proxy CSCF
HSS
Ernie
User2@bert
HSS
Bert
Scenario 1: Registration
User1@ernie
Serving CSCF
Serving CSCF
Proxy CSCF
HSS
Ernie
User2@bert
HSS
Bert
User1@ernie calls User2@bert
User1@ernie
Serving CSCF
Serving CSCF
Proxy CSCF
HSS
Ernie
User2@bert
HSS
Bert
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
User1@ernie
Serving CSCF
Serving CSCF
Proxy CSCF
HSS
Ernie
User2@bert
HSS
Bert
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 !!