Telecommunication Services Engineering Labusers.encs.concordia.ca/~glitho/H010_Chapter12_INSE7110.pdf · UMTS (Universal Mobile Telecommunication Systems) - An example of 3G system:

Telecommunication Services Engineering Lab

Roch H. Glitho1


Layering in next generation networks

Services ( value-addedservices) also calledapplication / services

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application / services

Services (Basic service) also called call/session

Transport (Below IP + IP + transport layer) also calledbearer


Layering in next generation networks

Services

Infrastructural, application, middleware and baseware services

NGN

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.

Resources

Servicecontrol functions

Transportcontrol functions

Servicemanagement functions

Transportmanagement functions

NGNservice

NGNtransport

Transfer functional area

Resources


Layering in UMTS

UMTS (Universal Mobile Telecommunication Systems)

- An example of 3G system:

- Evolution of GSM

- Use of WCDMA

- Largest footprint

- Another example of 3G system- Evolution of CDMA-One

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- Evolution of CDMA-One

- Use of WCDMA, but a version incompatible with UMTS

- Dwindling footprint


Layering in UMTS


- UMTS transport:

- TCP

- IP

- Below IP

- WCDMA

- Bandwidth (Peak rate: single digit Mbits/s – usually lower than 2)

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Layering in UMTS


- UMTS Service:

- IP Multimedia Subsystem (IMS)

- Basic service (call / session or control layer)

- Value added services (value added service or service layer)

- Focus of this lecture: IMS

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IMS

1. Overall view

2. Control layer

3. Service layer

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3. Service layer


Overall view

1. General picture

2. Simplified picture

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General picture

C x

I P M u l t im e d ia N e tw o r k s

P S T N

M m

M b

L e g a c y m o b i le

s ig n a l l in g N e tw o r k s

C S C F

M w

B G C FM j

M i

B G C F

M k M k

C , D ,

G c , G r

M b P S T N

P S T N

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P - C S C F

C S C FM G C F H S S

C x

I M S -

M G WM n

M b

M g

M R F P

M b

M r

G o

P D F

M w

G mU E

M b

M b

M R F C

S L F

D x

M p

I M S u b s y s te m

A S

I S C

D h S h ,S i


Simplified picture

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.


Another simplified picture

S - C S C F S - C S C F

S IP A p pli c a t io n S e rv e r


H S S H S S O SA s erv ice

cap ab ilit y s erv er (SC S)

O SA s erv ice cap ab ilit y s erv er

(SC S)

O SA ap p licat io n

s erv er


s erv er

IS C

C x IS C

S C IM

A S A S

S h

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(SC S) (SC S)

IM - S S F IM - S S F

C am el Serv i ce E n v iro n m en t


s erv er s erv er C x IS C

IS C

C A P

M A P

O SA AP I S i


Control layer

1. Functional entities

2. Protocols

3. Call cases

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Functional entities

Data bases (just one)

Home Subscriber Server (HSS)

- Evolution of the HLR

- All user related subscription data (e.g. profile)

- A network may contain one or several

- Subscriber Location Function (SLF) maps users to specific HSS

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HSS

.


Functional entities

Control entities

Call Session Control Function (CSCF) “The switch”

Three types (May be collocated)

- Proxy CSCF

- Serving CSCF

- Interrogating CSCF

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Functional entities

Control entities

Proxy-CSCF:

- Location

Either visited network or home network

- First contact point in the IM network

- Outbound / In-bound SIP proxy (All requests from/to IMS terminals go through it)

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terminals go through it)

- Forward SIP requests in the appropriate direction (Terminals or IMS network)

- Several functions

- Security

- Generation of charging information

- Compression and un-compression of messages


Functional entities

Control entities

Interrogating CSCF (I-CSCF):

SIP proxy located at the edge of an admnistrative domain

- Listed in the domain name server (DNS)

- There may be several in the same network for scalability reasons

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Functional entities

Control entities

Serving CSCF (S-CSCF):

Always located in home domain

SIP proxy + SIP registrar with possibility of performing session control

- Binding between IP address (terminal location) and user SIP address

- Interacts with application servers for value added service

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- Interacts with application servers for value added service purpose

- Translation services (Telephone number / Sip URIs)

- Routing


Functional entities

Control entities

Media Resource Function (MRF)

- Source of media (media mixing, announcement playing)

- Two parts

Control part: MRFC

Media Part: MRFP

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Functional entities

Control entities

Media Gateway Function (MGF):Signaling conversion between PSTN/2G and IMS

Media Gateway (MG)Media conversion between PSTN/2G and IMS

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Protocols

Signalling

SIP with extensions

Interactions with HSS

AAA

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Protocols

Example of SIP extension for IMS

Reliability of Provisional Responses for SIP

PRACK Method

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PRACK

- Bring more reliability by enabling the acknowledgement of provisional responses:

- Only final responses are acknowledged in standard SIP

- ACK for OK

- PRACK plays the same role as OK, but for provisional responses (e.g. 180 - ringing) except (100 – trying)

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PRACK

- Essential features

- Normal SIP request with its own response (i.e. OK)

- Each provisional response is given a sequence number Rseq

- PRACK contains a header Rack to indicate the sequence of the provisional response being acknowledged

- Caller indicates if it supports or not PRACK

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- Both parties can indicates if it is required or not



PRACK

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• http://www.dialogic.com/webhelp/IMG1010/10.5.1/WebHelp/Description/SIP/SIP_PRACK_Call_Flows.htm

.



PRACK

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PRACK

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Authentication, Authorization and Accounting

1. Informal definitions

2. AAA in Internet

3. AAA in IMS

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4. Call cses


Informal definitions

• Authentication– Means of verifying that an entity is really what it claims to be

• Authorization

– Means of ensuring that en entity does only what it is allowed to do

Accounting

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• Accounting

– Means of keeping track of what an entity does for auditing, billing and other purposes


AAA in Internet

Remote Authentication Dial In User Service (RADIUS) protocol– RFC 2058, then 2138, 1997

– RFC 2865, 2000

• Possibility for a Network Access Server (NAS) to get authentication, authorization and accounting (AAA) services from a RADIUS server

• Client/server

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• Client/server

• Runs on top of UDP

• Example: Computer with a modem, connected to a NAS and NAS connected to a RADIUS server

» Very useful when there are several NAS

.


AAA in Internet

Remote Authentication Dial In User Service (RADIUS) protocol

• Issues

– Lack of scalability

– Lack of functionality (e.g. no possibility for unsolicited messages from RADIUS server to NAS)

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AAA in Internet

Diameter– Addresses RADIUS shortcomings

• Scales

• More functionality

– Much more complex

• Base protocol, RFC 33588, 2003

– Basic commands (e.g. Re-Auth-Request, Re-Auth-Answer, Accounting-Request)

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Accounting-Request)

• Application protocols

– Extend the basic commands

.


AAA in IMS

• Interfaces

– Cx: I-CSCF / HSS and S-CSCF/HSS

– Dx: I-CSCF / SLF and S-CSCF / SLF

– Sh: HSS/SIP AS and HSS/OSA SCS

• Protocol

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• Protocol

– Diameter with IMS specific applications

.


IP Multimedia portion – Registration

.

P - C S C F H S SI - C S C F

1 . R e g i s t e r

2 . R e g i s t e r

3 . C x - Q u e r y

U E

V i s i t e d N e t w o r k H o m e N e t w o r k

4 . C x - Q u e r y R e s p

5 . C x - S e l e c t - p u l l

6 . C x - S e l e c t - p u l l R e s p

7 . R e g i s t e r

8 . C x - p u t

S - C S C F

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1 0 . C x - P u l l

1 1 . C x - P u l l R e s p

1 3 . 2 0 0 O K

1 4 . 2 0 0 O K1 5 . 2 0 0 O K

9 . C x - p u t R e s p

1 2 . S e r v i c e C o n t r o l


IP Multimedia portion – Un-Registration

.

P-CSCF HSSI-CSCFUE

Visited Network Home Network

1. REGISTER

2. REGISTER

3. Cx-Query

S-CSCF

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4. Cx-Query-Resp

5. REGISTER

9. 200 OK

10. 200 OK

11. 200 OK

7. Cx -Put

8. Cx -Put Resp

6. Service Control


Use of Megaco / H.248

– Interworking 3G/2G

• MGF

• MG

– Conferencing

• MRFC

• MRFP

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Service layer

1. Functional entities

2. Protocols

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Functional entities

Application server (AS)

Host services and execute services

Communicate with control layer using SIP (i.e. ISC interface)

Two types

SIP AS:

Open Service Architecture – Service Capability Server

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Open Service Architecture – Service Capability Server (OSA/SCS)


Functional entities

S - C S C F S - C S C F



H S S H S S O SA s erv ice

cap ab ilit y s erv er (SC S)

O SA s erv ice cap ab ilit y s erv er

(SC S)


s erv er


s erv er

IS C

C x IS C

S C IM

A S A S

S h

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(SC S) (SC S)

IM - S S F IM - S S F



s erv er s erv er C x IS C

IS C

C A P

M A P

O SA AP I S i


Functional entities

SIP AS

SIP servlets technology

Open Service Architecture – Service Capability Server (OSA/SCS)

Parlay / OSA technology

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Parlay / OSA technology


Protocols

ISC

SIP + extensions

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References

3GPP• K. Knightson, N. Morita and T. Towle, NGN Architecture: General Principles, Functional

Architecture and Implementation, IEEE Communications Magazine , October 2005, Vol.43, No10

• G. Camarillo and M. Garcia-Martin, The 3G IP Multimedia Subsystem, Wiley, 2004 , Part II

• M. Toy, H. Stuttgen and M. Ulema, guest editors, IP Multimedia Subsystems (IMS), IEEE Communications Magazine special issue, March 2007

• M. Toy, H. Stuttgen and M. Ulema, guest editors, IP Multimedia Subsystems (IMS), IEEE Communications Magazine special issue, July 2007

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Communications Magazine special issue, July 2007

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Telecommunication Services Engineering Labusers.encs.concordia.ca/~glitho/H010_Chapter12_INSE7110.pdf · UMTS (Universal Mobile Telecommunication Systems) - An example of 3G system:

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