IMS 3GPP & TISPAN multimedia network

grrrgrapeInternet and Web Development

Oct 31, 2013 (4 years and 12 days ago)

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CELLULAR COMMUNICATIONS

12. IMS

2

Existing Telecommunications


Benefits:


Worked well for stand
-
alone systems


Challenges:


Many Networks = High Operational and Interworking Costs


Slow to introduce new services


Users require different devices for different services

Difficult to integrate new services or technologies

Services

Transport


& Access

3

Emerging Telecommunications

Services and access technologies only need to interface to
the common transport layer (IP)

Access

Transport













Services

Internet

Protocol


Benefits:


Rapid Service Deployment = New Service Revenues


Allow continued growth of the network


Flexible architecture for future growth and new technologies


Allows for competition at individual layers


Challenges:


Legacy policy frameworks are challenged by the emerging
telecommunications model throughout the world

Source: ASTAP05/WS
-
IP&NGN/13

4

Access and Service Independence


Each service must be
integrated to a specific
access technology.


With many services
converging it becomes
complex to integrate
single access.




IP provides a common
interface for access and
services


One point of interface
simplifies the introduction
of new devices and
services.

video

data

voice

dsl

wi
-
fi

cable

Internet Protocol

video

data

voice

dsl

wi
-
fi

cable

Source: ASTAP05/WS
-
IP&NGN/13


What is IMS?

5

|
IMS in I&R
| January
2007


The “Internet Protocol Multimedia
Subsystem” (
IMS
) has been created for the
3G networks and is now considered to be
the standard for fix and mobile
Internet
-
based telephony by Operators
.


Developed in 3GPP (R5,R6,R7) since2001
but now adopted by 3GPP2(MMD in 2003)
ETSI/TISPAN R1(2005) & R2 (on going)



The protocols come from the IETF:


RTP

for media


SIP

for signaling/address resolution

6

RNC

MSC(Server)

SGSN

GGSN

CN

MGW

BSC

UMTS/GPRS

WLAN

Corporate

P
-
CSCF

I
-
CSCF

MRF

MGW

MGCF

IMS

S
-
CSCF

SIP Application

Servers

SIP Application

Servers

HSS

CDMA 2000

DSL/Cable Modem

DSLAM/CMTS

IMS Access Network Independence

Why IMS?

The Voice over IP: the impulse

7

|
IMS in I&R
| January
2007


After many other services, introduction of
voice/video calls on Internet


The 1
st

problem is easy: How to transmit
voice/video
?


RTP

(Real
-
Time Protocol) is a protocol which
transports an encoded multimedia stream as
pieces, with a timestamp on each piece, and
sends them using UDP/IP


Any encoding

is permitted for voice/video
with a Codec: MP3, ACC, MPEG4, AMR…


Several streams (
voice+video
) can be sent
in
parallel

with the same timestamp


The
timestamp

is used by the receiver to play
the voice/video in a regular way for quality


RTP is the
media transport

IP packets

Codec

RTP

UDP

IP

Why
IMS? Transmission
of voice/video is ok
, …
but transmission to
which IP
-
address?

8

|
IMS in I&R
| January
2007


The 2
nd

problem is
more difficult
:
how to initiate the call? how to know
the IP
-
address of the called phone?


It is necessary to have a
table

which
translates a symbolic name “Betty” into
an IP address


Each time a terminal service is put on,
it must notify its presence to update
the table


So, thanks to an access to this table, it
is possible to make the
address
resolution

: name
-
> IP address



The
control of the address table
creates a tough competition…

Registration of Betty’s phone
and address

Registration of John’s phone
and address

Why
IMS? Solutions
to make the
address resolutions

9

|
IMS in I&R
| January
2007


MSN, Yahoo, AOL have
designed a calling architecture
hyper
-
centralized
: 1 table
worldwide, only 1 operator



Skype promotes a
hyper
-
decentralized

architecture: 1
table per terminal with peer
-
to
-
peer update between
terminals

Operators dislike such approaches, so they push a way very
similar to e
-
mail:
centralization per domain
. This approach is
named “Internet Protocol Multimedia Subsystem”,
IMS
.

Why
IMS? SIP
(IETF) is replacing H323
signaling (ITU)


The Session Initiation Protocol (SIP) performs 1 function:
signaling.


SIP covers the registration for address resolution of
users/terminals as well as the call handling


In fact, Internet Telephony call processing is working on the
text of SIP messages to prepare the RTP voice/video
flows.


SIP is naturally integrated in Internet as an increment to
existing services


DNS “
url
” naming, like e
-
mail


Any transmission protocol. e.g., RTP


Any codec, voice/video


SIP messages are small texts

10

|
IMS in
I&R | January
2007

Introduction


SIP is the core protocol for initiating, managing and
terminating sessions in the Internet


These sessions may be text, voice, video or a
combination of these


SIP sessions involve one or more participants and
can use unicast or multicast communication.

SIP Message Types

Requests


sent from client to server


INVITE


ACK


BYE


CANCEL


OPTIONS


REGISTER


INFO


SIP Message Types (Contd.)

Responses


sent from server to the client


Success


Redirection


Forwarding


Request failure


Server failure


Global failure

Courtesy


The RADVISION SIP Whitepaper

SIP Session Establishment and Call Termination




From the RADVISION whitepaper on
SIP


John is calling Betty


introducing the
HSS and the S
-
CSCF

16

|
IMS in
I&R | January
2007


The
HSS

is the table user/address


The
S
-
CSCF

is a SIP proxy which works on messages
to provide users (consumers, enterprises) with calling
services including registration being a mediation
SIP2DIAMETER

SIP

HSS

S
-
CSCF

When the phones get
connected they register
their name/IP to the HSS

Changes the SIP message replacing “Betty”
by its IP address found in the HSS

SIP

John is calling a taxi to meet Betty


introducing the Application Server (AS)

17

|
IMS in
I&R | January
2007


In addition to the basic name/address translation, the S
-
CSCF routes
SIP messages to:


The network of Betty, if different


The applications such as: Push
-
To
-
Talk, Instant Messaging, Advance
Call Control, Voice/video mailbox, nearest Taxi… running on
AS
, a
SIP proxy application server

S
-
CSCF

AS



nearest Taxi application (location, fleet…)

Changes the SIP message replacing “taxi” by the
IP address of the nearest available taxi

John’s and Betty’s phones do not support a common
voice encoding


introducing the MRFC and MRFP

18

|
IMS in
I&R | January
2007


Intercepting the SIP “invite” message, the S
-
CSCF/AS detects a
non compatibility between the codecs of the phones : it forwards
it to the
MRFC

(a SIP proxy).


The MRFC adjusts the SIP messages in order to orient the RTP flow
to the
MRFP

(a RTP proxy), for transcoding

MRFC

MRFP

MGCP, H248 Megaco

RTP (codec: AMR)

SIP

S
-
CSCF

RTP (codec: G729)

During its travel John is calling Betty


introducing the P
-
CSCF


The operator has made a segmentation of its services offer


introducing the I
-
CSCF

19

|
IMS in
I&R |
January

2007


The
P
-
CSCF

is the
1
st

SIP proxy seen

by the terminal


It controls the bearer plan via COPS protocol


It adjusts the SIP message (e.g., compression) and forwards it to the I
-
CSCF of the home
network


The operator may have several S
-
CSCFs (e.g., offer segmentation)


So it introduces, the
I
-
CSCF

SIP proxy as the
entry point of its network


also used as the entry point for calls from other operators




Home Network

Visited Network

P
-
CSCF



S
-
CSCF (consumers)

S
-
CSCF (enterprises)

I
-
CSCF

HSS

John is calling Betty who has a legacy phone


introducing the MGCF and the MGW

20

|
IMS in
I&R | January
2007


At the
border

of the IMS network with the phone
network, an adaptation is necessary.


The
MGCF

handles the control for the 2 worlds and
drives the MGW (Media gateway)


… controls circuits and MGW much like a VoIP
softswitch

MGCF

MGW

H248 MGCP,

Megaco

SIP

Legacy Call control (SS7)

Phone transmission



Internet

PSTN/PLMN network

RTP

21

Visited

Network


UE

Home

Network


AS

SLF

HSS

GGSN

S
-
CSCF

P
-
CSCF

I
-
CSCF

Session control
services


Registration

AS interaction

Charging etc.

Access Point to
Network

Hides Topology &
Configuration

First Point of
Contact

Privacy Control &
QoS
Authorisation

Local Services:
Emergency &
Local Numbering

Diameter Protocol

SIP Protocol

IMS basic components

CSCF


Call State Control Functions

P


Proxy

I


Interrogating

S


Serving

UE


User Equipment

SLF
-

Subscriber

Location

Function

HSS
-

Home Subscriber Server

AS


Application

Server

Gateway GPRS
Support Node

Source: ASTAP05
-
WP.IP&NGN
-
08_ETSI

Simplified IMS architecture

22

|
IMS in
I&R | January
2007

Standardisation Overview

3GPP / TISPAN IMS Architectural Overview

23

|
IMS in
I&R | January
2007

This is only a logical

(functional) architecture,

not a physical one.

IMS
-
MGW

UE

IPv6 PDN

(IPv6 Network)

MGCF







PDF

I
-
CSCF

S
-
CSCF

BGCF

Application

(SIP AS,

OSA AS,

CAMEL SE)

MRFC

MRFP

MRF

BB

(IP v4/

IPv6)

P
-
CSCF

SGW

OSA SCS

IM SSF


SIP AS

AS

RAN

BG

IMS Session Signalling

IMS User Plane Data







HSS

‘IMS Data’

SLF

ALG

TrGW

IMS GW

IPv4 PDN

(IPv4 Network)

IPv4 based Signalling

IPv4 User Plane Data

PEF

CSCF

HLR/AuC (‘CS/PS’)

3gpp R5

WLAN

PDG

UE

WLAN WAG

3gpp R6

GGSN

SGSN

CS Networks

(PSTN, CS PLMN)

BAS

UE

DSLAM


3gpp R7 / TISPAN R1…

SPDF/ A
-
RACF

NASS

24

FUNCTIONAL ELEMENTS DESCRIPTIONS


Home Subscriber Server (HSS)


Application Server (AS)


Call Session Control Function (CSCF)


Breakout Gateway Control Function (BGCF)


Media Gateway Function (MGW)


Media Gateway Control Function (MGCF)


Multimedia Resource Function Controller (MRFC)


Multimedia Resource Function Processor (MRFP)


25

Home Subscriber Server (HSS)


Presence, Location and Profile


End
-
User Identity


Private and Public End
-
User Information


Registration Information


Service Initiation Information


Subscriber Service Profile (SSP)


Downloaded to CSCF at Registration

HSS

Diameter

26

Application Server (AS)


Contains Call Related Application Logic


Facilitates a Service Creation Environment


Queried by S
-
CSCF in Real Time to Execute
Logic


Generally Specialized for Each Service


May Provide Gateway to Legacy Applications
(e.g. AIN)

AS

AS

AS

SIP

Diameter

27

Call/Session Control Function (CSCF)


CSCF


Processes SIP Signaling


P
-
CSCF


First Point of User Contact


Authenticates user


May Include Policy Functions


C
-
CSCF


Central Node of Control Plane


Acts as Registar for User (Downloads SSP from HSS)


Invokes Application Servers


Performs Primary Routing Function


I
-
CSCF


Located at Edge of Administrative Domain


Is the Ingress Network Point Defined in DNS


Shields Network Topology from External Networks

I
-
CSCF

S
-
CSCF

P
-
CSCF

SIP

SIP

SIP

SIP

SIP

Diameter

28

PSTN (Circuit Switched) Gateway


BGCF


Routes to Gateway Based Upon
Telephone Number


MGCF


Controlling Function for SGW and
MGW


SGW


Provides Signaling Conversion Between
SIP and ISUP


MGW


Provides Conversion between RTP and
TDM



MGCF

MGW

H.248

ISUP

BGCF

SIP

SIP

TDM

SGW

SIP

29

Multimedia Resource Function (MRF)


Offers Services Such as Conferencing


MRFC


SIP User Interface toward S
-
CSCF


MRFP


Controls the Media Server (MS)

SIP

MS

MS

MRFC